___ - Hardy Wein. ___ - Transl. and transc. . ___-Dna Struc.,repli. ____- Mit. and Mio ____- Hum. Non-Dis. ____ - Traits, Domin., etc. ____-Gene Protein Rel. ___-Multiple alleles,c.dom,inc.dom,____ -Pedigree analysis, ____- mutations,___-Mendel
- chromosomes
The Hardy-Weinberg principle states that a population’s allele and genotype frequencies will remain constant in the absence of evolutionary mechanisms. Ultimately, the Hardy-Weinberg principle models a population without evolution under the following conditions: no mutations, no immigration/emigration, no
natural selection, no sexual selection, large population. The Hardy-Weinberg Principle: When populations are in the Hardy-Weinberg equilibrium, the allelic frequency is stable from generation to generation and the distribution of alleles can be determined. If the allelic frequency measured in the field differs from the
predicted value, scientists can make inferences about what evolutionary forces are at play. Applications of Hardy-Weinberg: The genetic variation of natural populations is constantly changing from genetic drift, mutation, migration, and natural and sexual selection. The Hardy-Weinberg principle gives scientists a
mathematical baseline of a non-evolving population to which they can compare evolving populations. If scientists record allele frequencies over time and then calculate the expected frequencies based on Hardy-Weinberg values, the scientists can hypothesize the mechanisms driving the population’s evolution. Mutation. Although
mutation is the original source of all genetic variation, mutation rate for most organisms is pretty low. So, the impact of brand-new mutations on allele frequencies from one generation to the next is usually not large. (However, natural selection acting on the results of a mutation can be a powerful mechanism of evolution!
Non-random mating. In non-random mating, organisms may prefer to mate with others of the same genotype or of different genotypes. Non-random mating won't make allele frequencies in the population change by itself, though it can alter genotype frequencies. This keeps the population from being in Hardy-Weinberg equilibrium,
but it’s debatable whether it counts as evolution, since the allele frequencies are staying the same. Gene flow. Gene flow involves the movement of genes into or out of a population, due to either the movement of individual organisms or their gametes (eggs and sperm, e.g., through pollen dispersal by a plant). Organisms and
gametes that enter a population may have new alleles, or may bring in existing alleles but in different proportions than those already in the population. Gene flow can be a strong agent of evolution. Non-infinite population size (genetic drift).Genetic drift involves changes in allele frequency due to chance events – literally, "sampling
error" in selecting alleles for the next generation. Drift can occur in any population of non-infinite size, but it has a stronger effect on small populations. We will look in detail at genetic drift and the effects of population size. Natural selection. Finally, the most famous mechanism of evolution! Natural selection occurs when one allele
(or combination of alleles of different genes) makes an organism more or less fit, that is, able to survive and reproduce in a given environment. If an allele reduces fitness, its frequency will tend to drop from one generation to the next. We will look in detail at different forms of natural selection that occur in populations. In
transcription, the DNA sequence of a gene is copied to make an RNA molecule. This step is called transcription because it involves rewriting, or transcribing, the DNA sequence in a similar RNA "alphabet." In eukaryotes, the RNA molecule must undergo processing to become a mature messenger RNA (mRNA). In translation,
the sequence of the mRNA is decoded to specify the amino acid sequence of a polypeptide. The name translation reflects that the nucleotide sequence of the mRNA sequence must be translated into the completely different "language" of amino acids.Transcription is the synthesis of RNA from DNA. Occurs in the nucleus.
Translation is the synthesis of a protein from RNA. In transcription, one strand of the DNA that makes up a gene, called the non-coding strand, acts as a template for the synthesis of a matching (complementary) RNA strand by an enzyme called RNA polymerase. This RNA strand is the primary transcript. The primary
transcript carries the same sequence information as the non-transcribed strand of DNA, sometimes called the coding strand. However, the primary transcript and the coding strand of DNA are not identical, thanks to some biochemical differences between DNA and RNA. Dna has Deoxyribose while rna has ribose
sugar.Deoxyribose has one less sugar than ribose. One important difference is that RNA molecules do not include the base thymine (T). Instead, they have a similar base uracil (U). Like thymine, uracil pairs with adenine. In bacteria, the primary RNA transcript can directly serve as a messenger RNA, or mRNA.
Messenger RNAs get their name because they act as messengers between DNA and ribosomes. Ribosomes are RNA-and-protein structures in the cytosol where proteins are actually made.In eukaryotes (such as humans), a primary transcript has to go through some extra processing steps in order to become a mature mRNA. During
processing, caps are added to the ends of the RNA, and some pieces of it may be carefully removed in a process called splicing. During translation, the nucleotide sequence of an mRNA is translated into the amino acid sequence of a polypeptideTranslation – genetic code used to form amino acid sequence using M-RNA, T-RNA,
and RRNA – it occurs in the cytoplasm at the ribosome.Specifically, the nucleotides of the mRNA are read in triplets (groups of three) called codons. Codons are a sequence of three nucleotides which together form a unit of genetic code in a DNA or RNA molecule.There are 61 codons that specify amino acids. One codon is a
"start" codon that indicates where to start translation. The start codon specifies the amino acid methionine, so most polypeptides begin with this amino acid. Three other “stop” codons signal the end of a polypeptide. These relationships between codons and amino acids are called the genetic code.
Polymerase chain reaction (PCR) is a common laboratory technique used to make many copies (millions or billions!) of a particular region of DNA.Polymerase Chain Reaction (PCR) · Technique for quickly making an unlimited number of copies of any piece of DNA · Sometimes called "molecular photocopying.This DNA region
can be anything the experimenter is interested in. For example, it might be a gene whose function a researcher wants to understand, or a genetic marker used by forensic scientists to match crime scene DNA with suspects. Typically, the goal of PCR is to make enough of the target DNA region that it can be analyzed or used in
some other way. For instance, DNA amplified by PCR may be sent for sequencing, visualized by gel electrophoresis, or cloned into a plasmid for further experiments. PCR is used in many areas of biology and medicine, including molecular biology research, medical diagnostics, and even some branches of ecology. Taq polymerase Like DNA replication in an organism, PCR requires a DNA polymerase enzyme that makes new strands of DNA, using existing strands as templates. The DNA polymerase typically used in PCR is called Taq polymerase, after the heat-tolerant bacterium from which it was isolated (Thermus aquaticus). T. aquaticus lives in hot springs
and hydrothermal vents. Its DNA polymerase is very heat-stable and is most active around 70 (a temperature at which a human or E. coli DNA polymerase would be nonfunctional). This heat-stability makes Taq polymerase ideal for PCR. As we'll see, high temperature is used repeatedly in PCR to denature the template DNA,
or separate its strands. PCR primers - Like other DNA polymerases, Taq polymerase can only make DNA if it's given a primer, a short sequence of nucleotides that provides a starting point for DNA synthesis. In a PCR reaction, the experimenter determines the region of DNA that will be copied, or amplified, by the primers she or he
chooses. PCR primers are short pieces of single-stranded DNA, usually around 20 nucleotides in length. Two primers are used in each PCR reaction, and they are designed so that they flank the target region (region that should be copied). That is, they are given sequences that will make them bind to opposite
strands of the template DNA, just at the edges of the region to be copied. The primers bind to the template by complementary base pairing. This cycle repeats 25 - 35 times in a typical PCR reaction, which generally takes 2 - 4 hours, depending on the length of the DNA region being copied. If the reaction is efficient
(works well), the target region can go from just one or a few copies to billions. That’s because it’s not just the original DNA that’s used as a template each time. Instead, the new DNA that’s made in one round can serve as a template in the next round of DNA synthesis. There are many copies of the primers and many molecules
of Taq polymerase floating around in the reaction, so the number of DNA molecules can roughly double in each round of cycling.The single-ring nitrogenous bases, thymine and cytosine, uracil are called pyrimidines, and the double-ring nitrogenous bases, adenine and guanine, are called purines. Adenine and Thymine have 2
hydrogen bonds while cytosine and guanine have 3 hydrogen bonds. During transcription, the RNA polymerase reads the template DNA strand in the 3′→5′ direction, but the mRNA is formed in the 5′ to 3′ direction. ... The codons of the mRNA reading frame are translated in the 5′→3′ direction into amino acids by a
ribosome to produce a polypeptide chain.A peptide is two or more amino acids joined together by peptide bonds; a polypeptide is a chain of many amino acids; and a protein contains one or more polypeptides. Therefore, proteins are long chains of amino acids held together by peptide bonds.In transcription, the DNA
sequence of a gene is copied to make an RNA molecule. This step is called transcription because it involves rewriting, or transcribing, the DNA sequence in a similar RNA "alphabet." In eukaryotes, the RNA molecule must undergo processing to become a mature messenger RNA (mRNA). In translation, the sequence of the
mRNA is decoded to specify the amino acid sequence of a polypeptide. The name translation reflects that the nucleotide sequence of the mRNA sequence must be translated into the completely different "language" of amino acidsIn transcription, one strand of the DNA that makes up a gene, called the non-coding strand, acts as
a template for the synthesis of a matching (complementary) RNA strand by an enzyme called RNA polymerase. This RNA strand is the primary transcript.The start codon is the first codon of a messenger RNA transcript translated by a ribosome. The start codon always codes for methionine in eukaryotes and Archaea and a
modified Met in bacteria, mitochondria and plastids. The most common start codon is AUG. The start codon is often preceded by a 5' untranslated region.Each of the three base codon on the messenger RNA (m-RNA) is a code for an amino acid.There are 64 possible three base codons – 61 area codes for one of the 20
amino acids.The three remaining codons are termed stop codons because the signal the end of a peptide segment.Notice that many of the amino acids have more than one codon.A three base code on the DNA produces the mRNA codon. Transcription: Synthesis of RNA from a DNA Template. ·Requires DNA-dependent RNA
polymerase plus the four nucleotides (ATP, GTP. CTP and UTP). ·Synthesis begins at the initiation site on DNA ·The template strand is read 3' to 5' and the mRNA is synthesized 5' to 3'. Types of RNA – three kinds of RNA-Messenger RNA – carries genetic code from DNA into cytoplasm.Transfer RNA – transfers amino
acids for building of protein.Ribosomal RNA – reads the code of M-RNA and allows T-RNA to attach. Post-transcriptional Modifications-RNA’s are modified in eukaryotes before leaving the nucleus. PreM-RNA has exons (coding segments) and introns (noncoding segments between exons),introns (the non coding segments)
are removed, a cap is added to the 5’ end,a poly A tail is added to the 3’ end before it leaves the nucleus.DNA is made up of molecules called nucleotides. Each nucleotide contains a phosphate group, a sugar group and a nitrogen base. The four types of nitrogen bases are adenine (A), thymine (T), guanine (G) and cytosine
(C).Phoebus Levene's Tetranucleotide Hypothesis- Following establishment that nucleic acids were localized in the chromosomes, early experiments suggested that the four base molecules A-T, C-G occur in approximately equal ratios.The Russian-American biochemist Phoebus Levene (1869-1940), who had discovered ribose
sugar in 1909 and deoxyribose sugar in 1929, suggested the structure of nucleic acid as a repeating tetramer. He called the phosphate - sugar - base unit a nucleotide. The simplicity of this structure implied that nucleic acids were too uniform to contribute to complex genetic variation. Attention thereafter focused on protein as the
probable hereditary substance.The order of these bases is what determines DNA's instructions, or genetic code.The DNA structure of a eukaryotic cell is a right handed double helix.Double Helix -James Watson and Francis Crick are usually given credit for discovering that DNA has a double helix shape, like a spiral
staircase . The discovery was based on the prior work of Rosalind Franklin and other scientists, who had used X rays to learn more about DNA’s structure. Franklin and these other scientists have not always been given credit for their contributions. The Discovery of DNA's Structure-Created by Rosalind Franklin using a
technique called X-ray crystallography, it revealed the helical shape of the DNA molecule. Watson and Crick realized that DNA was made up of two chains of nucleotide pairs that encode the genetic information for all living things.Each time a cell divides, each of its double strands of DNA splits into two single strands. Each of these
single strands acts as a template for a new strand of complementary DNA. As a result, each new cell has its own complete genome. Genome means all genes in an organism.This process is known as DNA replication.In DNA replication the number of chromosomes stay the same(46) but the number of chromatids double(from 46
to 92). DNA replication is a semi-conservative process because half of the parent DNA molecule is conserved in each of the two daughter DNA molecules.This means that each of the two strands in double-stranded DNA acts as a template to produce two new strands.Replication relies on complementary base pairing, that is
the principle explained by Chargaff's rules: adenine (A) always bonds with thymine (T) and cytosine (C) always bonds with guanine (G). The primary enzyme involved in this is DNA polymerase which joins nucleotides to synthesize the new complementary strand. DNA polymerase also proofreads each new DNA strand to make sure
that there are no errors. DNA replication is able to replicate 8 billion nucleotides in about 6-8 hours because replication begins in multiple places on the chromosome. Helicase "unzip" DNA molecules by breaking the hydrogen bonds that hold the two strands together. One new strand, the leading strand, runs 5' to 3' towards the
fork and is made continuously.The other, the lagging strand, runs 5' to 3' away from the fork and is made in small pieces called Okazaki fragments.DNA replication occurs during interphase. Replication is controlled by the Watson-Crick pairing of the bases in the template strand with incoming deoxynucleoside
triphosphates, and is directed by DNA polymerase enzymes. It is a complex process, particularly in eukaryotes, involving an array of enzymes.The leading strand is synthesized continuously but the opposite strand is copied in short bursts of about 1000 bases, as the lagging strand template becomes available. The resulting short
strands are called Okazaki fragments known as the lagging strand (after their discoverers, Reiji and Tsuneko Okazaki). Bacteria have at least three distinct DNA polymerases: Pol I, Pol II and Pol III; it is Pol III that is largely involved in chain elongation. Strangely, DNA polymerases cannot initiate DNA synthesis de novo,
but require a short primer with a free 3′-hydroxyl group. This is produced in the lagging strand by an RNA polymerase (called DNA primase) that is able to use the DNA template and synthesize a short piece of RNA around 20 bases in length. Pol III can then take over, but it eventually encounters one of the previously
synthesized short RNA fragments in its path. At this point Pol I takes over, using its 5′- to 3′-exonuclease activity to digest the RNA and fill the gap with DNA until it reaches a continuous stretch of DNA. This leaves a gap between the 3′-end of the newly synthesized DNA and the 5′-end of the DNA previously synthesized by
Pol III. The gap is filled by DNA ligase, an enzyme that makes a covalent bond between a 5′-phosphate and a 3′-hydroxyl group (Figure 3). The initiation of DNA replication at the leading strand is more complex and is discussed in detail in more specialized texts.Dna Replication - 1.Initiation -DNA synthesis is initiated at
particular points within the DNA strand known as ‘origins’, which are specific coding regions. These origins are targeted by initiator proteins, which go on to recruit more proteins that help aid the replication process, forming a replication complex around the DNA origin. There are multiple origin sites, and when replication of DNA
begins, these sites are referred to as.The point where the splitting starts is known as the replication fork, has a top strand, called the leading strand, and another bottom strand called the lagging strand.These unwound sections can now be used as templates to create two complementary DNA strands.For the leading
strand an enzyme called DNA polymerase just adds matching nucleotides onto the main stem all the way down the molecule.But before it can do that it needs a section of nucleotides that fill in the section that's just been unzipped.Starting at the very beginning of the DNA molecule, DNA polymerase needs a bit of aprimer, just a
little thing for it to hook on to so that it can start building the new DNA chain.And for that little primer, we can thank the enzyme RNA primase.The leading strand only needs this RNA primer once at the very beginning.Then DNA polymerase is just follows the unzipping, adding new nucleotides to the new chain continuously,all
the way down the molecule.Within the replication complex is the enzyme DNA Helicase, which unwinds the double helix and exposes each of the two strands, so that they can be used as a template for replication. It does this by hydrolysing the ATP used to form the bonds between the nucleobases, therefore breaking the bond
between the two strands.DNA can only be extended via the addition of a free nucleotide triphosphate to the 3’- end of a chain. As the double helix runs antiparallel, but DNA replication only occurs in one direction, it means growth of the two new strands is very different (and will be covered in Elongation).DNA Primase is another
enzyme that is important in DNA replication. It synthesises a small RNA primer, which acts as a ‘kick-starter’ for DNA Polymerase. DNA Polymerase is the enzyme that is ultimately responsible for the creation and expansion of the new strands of DNA. 2.Elongation-Once the DNA Polymerase has attached to the original,
unzipped two strands of DNA (i.e. the template strands), it is able to start synthesising the new DNA to match the templates. This enzyme is only able to extend the primer by adding free nucleotides to the 3’-end of the strand, causing difficulty as one of the template strands has a 5’-end from which it needs to extend
from.One of the templates is read in a 3’ to 5’ direction, which means that the new strand will be formed in a 5’ to 3’ direction (as the two strands are antiparallel to each other). This newly formed strand is referred to as the Leading Strand. Along this strand, DNA Primase only needs to synthesise an RNA primer once, at the
beginning, to help initiate DNA Polymerase to continue extending the new DNA strand. This is because DNA Polymerase is able to extend the new DNA strand normally, by adding new nucleotides to the 3’ end of the new strand (how DNA Polymerase usually works).However, the other template strand is antiparallel, and is therefore
read in a 5’ to 3’ direction, meaning the new DNA strand being formed will run in a 3’ to 5’ direction. This is an issue as DNA Polymerase doesn’t extend in this direction. To counteract this, DNA Primase synthesizes a new RNA primer approximately every 200 nucleotides, to prime DNA synthesis to continue extending from the 5’ end
of the new strand. To allow for the continued creation of RNA primers, the new synthesis is delayed and is such called the Lagging Strand.The leading strand is one complete strand, while the lagging strand is not. It is instead made out of multiple ‘mini-strands’, known as Okazaki fragments. These fragments occur due to the
fact that new primers are having to be synthesised, therefore causing multiple strands to be created, as opposed to the one initial primer that is used with the leading strand. 3.Termination-The process of expanding the new DNA strands continues until there is either no more DNA template left to replicate (i.e. at the end of the
chromosome), or two replication forks meet and subsequently terminate. The meeting of two replication forks is not regulated and happens randomly along the course of the chromosome. Once DNA synthesis has finished, it is important that the newly synthesised strands are bound and stabilized. With regards to the
lagging strand, two enzymes are needed to achieve this; RNAase H removes the RNA primer that is at the beginning of each Okazaki fragment, and DNA Ligase joins two fragments together creating one complete strand. Now with two new strands being finally finished, the DNA has been successfully replicated, and will just need
other intrinsic cell systems to ‘proof-read’ the new DNA to check for any errors in replication, and for the new single strands to be stabilized.DNA Replication - · DNA uncoils and splits,Template strand is read 3’ to 5’,New complementary strand must add new nucleotides to the 3’ end – ,New nucleotides added 5’ to 3’,Leading strand
(continuous),Lagging strand adds fragments (Okazaki fragments),Fragments attached with the enzyme ligase.DNA ligase is an enzyme which can connect two strands of DNA together by forming a bond between the phosphate group of one strand and the deoxyribose group on another. It is used in cells to join together the
Okazaki fragments which are formed on the lagging strand during DNA replication.A DNA helicase is an enzyme that functions by melting the hydrogen bonds that hold the DNA into the double helix structure. The area of the DNA where the DNA helicase has unzipped the DNA is known as a replication fork. Helicases are a
class of enzymes vital to all organisms. Their main function is to unpackage an organism's genes. They are motor proteins that move directionally along a nucleic acid phosphodiester backbone, separating two annealed nucleic acid strands using energy from ATP hydrolysis.Topoisomerases are enzymes that participate in the
overwinding or underwinding of DNA. The winding problem of DNA arises due to the intertwined nature of its double-helical structure. During DNA replication and transcription, DNA becomes overwound ahead of a replication fork.DNA polymerase is an enzyme that synthesizes DNA molecules from deoxyribonucleotides, the
building blocks of DNA. These enzymes are essential for DNA replication and usually work in pairs to create two identical DNA strands from a single original DNA molecule. Cell Cycle – the life cycle of a cell.G0 Phase– Cells that go into this phase when not actively reproducing as muscle or nerve cells. G1 Phase – high rate of
biosynthesis and growth. S Phase – DNA content doubles and chromosomes replicate. G2 Phase - final preparations for Mitosis. G2 -stage of the cell cycle is needed to prepare for reproduction.M Phase – Mitosis and Cytokinesis.DNA Repair - Genes encode proteins that correct mistakes in DNA caused by incorrect copying
during replication and environmental factors such as by-products of metabolism, exposure to ultraviolet light or mutagens. The DNA repair process must operate constantly to correct any damage to the DNA as soon as it occurs. DNA Repair - Genes encode proteins that correct mistakes in DNA caused by incorrect copying during
replication and environmental factors such as by-products of metabolism, exposure to ultraviolet light or mutagens. The DNA repair process must operate constantly to correct any damage to the DNA as soon as it occurs. Alec Jefferreys invented DNA profiling.DNA profiling is the process of determining an individual's DNA
characteristics. DNA analysis intended to identify a species, rather than an individual, is called DNA barcoding. DNA, as a nucleic acid, is made from nucleotide monomers, and the DNA double helix consists of two polynucleotide chains. Each nucleotide consists of a sugar (deoxyribose), a phosphate group, and a
nitrogen-containing base (A, C, G, or T).DNA replication is the process in which DNA is copied. It occurs during the synthesis (S) phase of the eukaryotic cell cycle. DNA replication begins when an enzyme, DNA helicase, breaks the bonds between complementary bases in DNA.This exposes the bases inside the molecule so
they can be “read” by another enzyme, DNA polymerase, and used to build two new DNA strands with complementary bases, also by DNA polymerase. The two daughter molecules that result each contain one strand from the parent molecule and one new strand that is complementary to it. As a result, the two daughter molecules
are both identical to the parent molecule. Mitosis is a process where a single cell divides into two identical daughter cells (cell division). During mitosis one cell divides once to form two identical cells.The major purpose of mitosis is for growth and to replace worn out cells.It takes 2 hours for mitosis to be completed.If
not corrected in time, mistakes made during mitosis can result in changes in the DNA that can potentially lead to genetic disorders.Interphase is not part of mitosis. Mitosis is divided into four phases: 1. Interphase(not a part of mitosis):The DNA in the cell is copied in preparation for cell division, this results in two
identical full sets of chromosomes.Interphase (late G2 phase) has already copied its DNA, so the chromosomes in the nucleus each consist of two connected copies, called sister chromatids. You can’t see the chromosomes very clearly at this point, because they are still in their long, stringy, decondensed form. Outside of the
nucleus are two centrosomes, each containing a pair of centrioles, these structures are critical for the process of cell division. During interphase, microtubules extend from these centrosomes.2. Prophase: The chromosomes condense into X-shaped structures that can be easily seen under a microscope. Each chromosome is
composed of two sister chromatids, containing identical genetic information. The chromosomes pair up so that both copies of chromosome 1 are together, both copies of chromosome 2 are together, and so on. At the end of prophase the membrane around the nucleus in the cell dissolves away releasing the
chromosomes. Early prophase - The mitotic spindle starts to form, the chromosomes start to condense, and the nucleolus disappears. In early prophase, the cell starts to break down some structures and build others up, setting the stage for division of the chromosomes.The chromosomes start to condense (making them easier to
pull apart later on).The mitotic spindle begins to form. The spindle is a structure made of microtubules, strong fibers that are part of the cell’s “skeleton.” Its job is to organize the chromosomes and move them around during mitosis. The spindle grows between the centrosomes as they move apart.The nucleolus (or nucleoli, plural),
a part of the nucleus where ribosomes are made, disappears. This is a sign that the nucleus is getting ready to break down. Late prophase (prometaphase)-The nuclear envelope breaks down and the chromosomes are fully condensed.In late prophase (sometimes also called prometaphase), the mitotic spindle begins to capture
and organize the chromosomes.The chromosomes finish condensing, so they are very compact.The nuclear envelope breaks down, releasing the chromosomes.The mitotic spindle grows more, and some of the microtubules start to “capture” chromosomes. The mitotic spindle, consisting of microtubules and other proteins, extends
across the cell between the centrioles as they move to opposite poles of the cell.3. Metaphase: The chromosomes line up neatly end-to-end along the centre (equator) of the cell.The centrioles are now at opposite poles of the cell with the mitotic spindle fibres extending from them. The mitotic spindle fibres attach to each of the
sister chromatids. Metaphase. Chromosomes line up at the metaphase plate, under tension from the mitotic spindle. The two sister chromatids of each chromosome are captured by microtubules from opposite spindle poles.In metaphase, the spindle has captured all the chromosomes and lined them up in the middle of the cell,
ready to divide.All the chromosomes align at the metaphase plate (not a physical structure, just a term for the plane where the chromosomes line up).At this stage, the two kinetochores of each chromosome should be attached to microtubules from opposite spindle poles.Before proceeding to anaphase, the cell will check to make
sure that all the chromosomes are at the metaphase plate with their kinetochores correctly attached to microtubules. This is called the spindle checkpoint and helps ensure that the sister chromatids will split evenly between the two daughter cells when they separate in the next step. If a chromosome is not properly aligned or
attached, the cell will halt division until the problem is fixed.4. Anaphase: The sister chromatids are then pulled apart by the mitotic spindle which pulls one chromatid to one pole and the other chromatid to the opposite pole. 5. Telophase:At each pole of the cell a full set of chromosomes gather together. A membrane forms
around each set of chromosomes to create two new nuclei. Cytokinesis-The single cell then pinches in the middle to form two separate daughter cells each containing a full set of chromosomes within a nucleus.Cytokinesis in an animal cell: an actin ring around the middle of the cell pinches inward, creating an indentation
called the cleavage furrow.In cytokinesis, there is a constriction of the cytoplasm and the cell finally splits. Cytokinesis in a plant cell: the cell plate forms down the middle of the cell, creating a new wall that partitions it in two.Cytokinesis, the division of the cytoplasm to form two new cells, overlaps with the final stages of
mitosis. It may start in either anaphase or telophase, depending on the cell, and finishes shortly after telophase.In animal cells, cytokinesis is contractile, pinching the cell in two like a coin purse with a drawstring. The “drawstring” is a band of filaments made of a protein called actin, and the pinch crease is known as the
cleavage furrow. Plant cells can’t be divided like this because they have a cell wall and are too stiff. Instead, a structure called the cell plate forms down the middle of the cell, splitting it into two daughter cells separated by a new wall.When division is complete, it produces two daughter cells. Each daughter cell has a
complete set of chromosomes, identical to that of its sister (and that of the mother cell). The daughter cells enter the cell cycle in G1.When cytokinesis finishes, we end up with two new cells, each with a complete set of chromosomes identical to those of the mother cell. The daughter cells can now begin their own cellular
“lives,” and – depending on what they decide to be when they grow up – may undergo mitosis themselves, repeating the cycle. Meiosis is a process where a single cell divides twice to produce four cells containing half the original amount of genetic information.Meiosis-When a cell duplicates its DNA and divides twice to produce
four gametes, or reproductive cells, the process is called meiosis. Most cells in the body are diploid, meaning they have two copies of each chromosome. But because gametes have gone through meiosis, they have one copy of each chromosome and are haploid. During sexual reproduction two gametes, called the egg and sperm,
join together and form a diploid cell that will eventually become an individual organism. This diploid cell, called a zygote, received one copy of each chromosome from each parent. The appearance, or phenotype, of the new individual will depend on whether it inherited recessive or dominant copies of various alleles from its
parents. Variant copies of genes are called alleles, and since plants and animals are diploid they have two alleles for each gene. Meiosis generates genetic diversity-Homologous chromosome pair crossing over in meiosis I, Random alignment of maternal and paternal chromosomes in meiosis I,Random alignment of sister
chromatids in meiosis II.It takes 74 hours for meiosis. These cells are our sex cells – sperm in males, eggs in females. During meiosis one cell divides twice to form four daughter cells. These four daughter cells only have half the number of chromosomes of the parent cell – they are haploid. Meiosis produces our sex cells or
gametes (eggs in females and sperm in males). Meiosis can be divided into nine stages. These are divided between the first time the cell divides (meiosis I) and the second time it divides (meiosis II):Meiosis I-1. Interphase:The DNA in the cell is copied resulting in two identical full sets of chromosomes. Outside of the nucleus
are two centrosomes, each containing a pair of centrioles, these structures are critical for the process of cell division. During interphase, microtubules extend from these centrosomes. 2. Prophase I - in this phase the nuclear membrane dissolves, chromosomes develop from the chromatin, and the centrosomes push apart,
creating the spindle apparatus. Homologous (similar) chromosomes from both parents pair up and exchange DNA in a process known as crossing over. This results in genetic diversity. These paired up chromosomes—two from each parent—are called tetrads. The copied chromosomes condense into X-shaped structures that can be
easily seen under a microscope. Each chromosome is composed of two sister chromatids containing identical genetic information. The chromosomes pair up so that both copies of chromosome 1 are together, both copies of chromosome 2 are together, and so on. The pairs of chromosomes may then exchange bits of DNA in a
process called recombination or crossing over. At the end of Prophase I the membrane around the nucleus in the cell dissolves away, releasing the chromosomes. The meiotic spindle, consisting of microtubules and other proteins, extends across the cell between the centrioles. 3. Metaphase I:some of the spindle fibers attach to
the chromosomes' centromeres. The fibers pull the tetrads into a vertical line along the center of the cell. The chromosome pairs line up next to each other along the centre (equator) of the cell. The centrioles are now at opposite poles of the cell with the meiotic spindles extending from them. The meiotic spindle fibres attach to one
chromosome of each pair. 4. Anaphase I: The pair of chromosomes are then pulled apart by the meiotic spindle, which pulls one chromosome to one pole of the cell and the other chromosome to the opposite pole. In meiosis I the sister chromatids stay together. This is different to what happens in mitosis and meiosis II. 5.
Telophase I and cytokinesis: The chromosomes complete their move to the opposite poles of the cell. At each pole of the cell a full set of chromosomes gather together. A membrane forms around each set of chromosomes to create two new nuclei. The single cell then pinches in the middle to form two separate daughter cells
each containing a full set of chromosomes within a nucleus. This process is known as cytokinesis. Meiosis II- 6.Prophase II: Now there are two daughter cells, each with 23 chromosomes (23 pairs of chromatids). In each of the two daughter cells the chromosomes condense again into visible X-shaped structures that can be
easily seen under a microscope. The membrane around the nucleus in each daughter cell dissolves away releasing the chromosomes. The centrioles duplicate. The meiotic spindle forms again.7. Metaphase II: In each of the two daughter cells the chromosomes (pair of sister chromatids) line up end-to-end along the equator of the
cell. The centrioles are now at opposite poles in each of the daughter cells.Meiotic spindle fibres at each pole of the cell attach to each of the sister chromatids. 8. Anaphase II: The sister chromatids are then pulled to opposite poles due to the action of the meiotic spindle. The separated chromatids are now individual
chromosomes.9.Telophase II and cytokinesis: The chromosomes complete their move to the opposite poles of the cell.At each pole of the cell a full set of chromosomes gather together.A membrane forms around each set of chromosomes to create two new cell nuclei.This is the last phase of meiosis, however cell division is not
complete without another round of cytokinesis. Once cytokinesis is complete there are four granddaughter cells, each with half a set of chromosomes (haploid): in males, these four cells are sperm cells. In females, one of the cells is an egg cell while the other three are polar bodies (small cells that do not develop into eggs).Meiosis
has two rounds of genetic separation and cellular division while mitosis only has one of each. In meiosis homologous chromosomes separate leading to daughter cells that are not genetically identical. In mitosis the daughter cells are identical to the parent as well as to each other. The different result of meiosis II in females
and males is that in females, four egg cells are produced but only one mature “usable” egg cell is produced. In males, four normal sperm cells are produced.Stages of Meiosis II- In prophase 2, centrosomes form and push apart in the two new cells.A spindle apparatus develops, and the cells' nuclear membranes dissolve.
Spindle fibers connect to chromosome centromeres in metaphase 2 and line the chromosomes up along the cell equator.During anaphase 2, the chromosomes' centromeres break, and the spindle fibers pull the chromatids apart.The two split portions of the cells are officially known as "sister chromosomes" at this point. As in
telophase 1, telophase 2 is aided by cytokinesis, which splits both cells yet.resulting in four haploid cells called gametes. Nuclear membranes develop in these cells, which again enter their own interphases.The structure formed in Prophase I of meiosis that has 4 homologous chromatids is called a tetrad.
Nondisjunction is the failure of homologous chromosomes or sister chromatids to separate properly during cell division. Nondisjunction occurs in the reproductive cells/gametes and results in an abnormal amount of chromosomes.Nondisjunction in meiosis II results from the failure of the sister chromatids to separate during
anaphase II. Aneuploidy is the presence of an abnormal number of chromosomes in a cell, for example a human cell having 45 or 47 chromosomes instead of the usual 46.Down Syndrome – (autosome) - three copies of chromosome 21: Karyotype showing 47 chromosomes (Trisomy 21), Results in various degrees of mental
disabilities cause decrease immunities to diseases/organ defects, distinguished facial features, affect 1:700 children and alters the child's phenotype either moderately or severely, affects how the child looks and learns. Edward’s Syndrome – (autosome) three copies of chromosome 18: Karyotype showing 47 chromosomes
(Trisomy 18),Results in failure of all organ systems, death after a few months,almost every organ system affected 1:10,000 live births,Children with full Trisomy 18 generally do not live more than a few months. Turner’s Syndrome (Monsonomy X)(XO) – (sex chromosome) – only one X chromosome is inherited:Karyotype 45,
X,Results in sterile female, short in stature, heart and kidney defects,Turner syndrome can cause a variety of medical and developmental problems, including short height, failure of the ovaries to develop and heart defects, neck problems.It causes errors during fetal development and other problems after birth — for example, short
stature, ovarian insufficiency, and heart defects. Physical characteristics and health complications that arise from the chromosomal error vary greatly.“Superfemale” – (sex chromosome) – extra X chromosome is inherited:Karyotype 47, XXX (Trisomy X), Results in healthy, fertile female, 1:5000 live births; the only viable monosomy
in humans, they do not mature sexually during puberty and are sterile, Short stature and normal intelligence. (98% of these fetuses die before birth). Klinefelter’s Syndrome – (sex chromosome) –extra X chromosome(s) is/are inherited: Karyotype 47, XXY (or even 48, XXXY; 49, XXXXY), Usually results in sterile male, Male sex
organs; unusually small testes, sterile. Breast enlargement and other feminine body characteristics, Normal intelligence, Individuals are somewhat taller than average and often have below-normal intelligence, goes through puberty at slower rate, and may not be able to have children. “Supermale” – (sex chromosome) – extra Y
chromosome is inherited: Karyotype 47, XYY, Usually results in sterile, more violent, decreased intelligence, taller male, They may include being taller than average, acne, and an increased risk of learning problems. The person is generally otherwise normal, including normal fertility. Patau syndrome (trisomy 13): Trisomy 13
causes severe intellectual disability and many physical abnormalities, such as congenital heart defects; brain or spinal cord abnormalities; very small or poorly developed eyes (microphthalmia); extra fingers or toes; cleft lip with or without cleft palate; and weak muscle tone (hypotonia). 1:5000 live births, Children rarely live for more
than a few months. Cri du chat syndrome , also known as 5p- (5p minus) syndrome or cat cry syndrome, is a genetic condition present from birth that is caused by the deletion of genetic material on the small arm (the p arm) of chromosome 5. Infants with this condition often have a high-pitched cry that sounds like that of a
cat.Other symptoms include microcephaly, and mental retardationƒ. Genetically, you actually carry more of your mother's genes than your father's. That's because of little organelles that live within your cells, the mitochondria, which you only receive from your mother. Your X chromosome is referred to as the egg cell
while the Y chromosome is referred to as the sperm cell. Genetically, you actually carry more of your mother's genes than your father's. That's because of little organelles that live within your cells, the mitochondria, which you only receive from your mother. Polygenic traits are traits that are controlled by multiple genes
instead of just one. The genes that control them may be located near each other or even on separate chromosomes. Because multiple genes are involved, polygenic traits do not follow Mendel’s pattern of inheritance. Instead of being measured discreetly, they are often represented as a range of
continuous variation. Some examples of polygenic traits are height, skin color, eye color, and hair color. Pleiotropy - refers to one gene that influences many traits. Example: If one gene determined two traits that were different from one another. Making up an easy example it could be one gene
determines both hair colour and length of claws in cats. Polygenic Inheritance - refers to many genes (2 or more) affecting one trait. The position of a gene on a particular chromosome is called the locus. The phenotype is the physical appearance of an organism, while the Genotype is the genetic
composition of an organism. An organism's genotype is the set of genes that it carries. An organism's phenotype is all of its observable characteristics.Phenotype - the physical expression of the genes for the trait by an individual. Genotype - the genetic makeup of an organism. Phenotype is the trait an individual
expresses while genotype is the two genes that cause that trait Punnett square - probability diagram illustrating the possible offspring of a mating male gene on top of columns and female traits on the side of rows. A and B genes are co-dominant and both dominant over the O gene which is recessive.
Independent Assortment – genes on different chromosomes separate independently during meiosis.Mendel's law of independent assortment states that the alleles of two (or more) different genes get sorted into gametes independently of one another. In other words, the allele a gamete receives for one gene does not
influence the allele received for another gene.Multiple alleles is a type of non-Mendelian inheritance pattern that involves more than just the typical two alleles that usually code for a certain characteristic in a species.With multiple alleles, that means there are more than two phenotypes available depending on the dominant or
recessive alleles that are available in the trait and the dominance pattern the individual alleles follow when combined together.Although individual humans (and all diploid organisms) can only have two alleles for a given gene, multiple alleles may exist in a population level, and different individuals in the population may have different
pairs of these alleles.The human ABO blood type is a good example of multiple alleles. Multiple Alleles - Alleles are alternative forms of a gene, and they are responsible for differences in phenotypic expression of a given trait (e.g., brown eyes versus green eyes). A gene for which at least two alleles exist is said to be
polymorphic. Instances in which a particular gene may exist in three or more allelic forms are known as multiple allele conditions. It is important to note that while multiple alleles occur and are maintained within a population, any individual possesses only two such alleles (at equivalent loci on homologous chromosomes). Examples
Of Multiple Alleles-Two human examples of multiple-allele genes are the genes of the ABO blood group system, and the human-leukocyte-associated antigen (HLA) genes. Incomplete dominance-Mendel’s results were groundbreaking partly because they contradicted the (then-popular) idea that parents' traits were permanently
blended in their offspring. In some cases, however, the phenotype of a heterozygous organism can actually be a blend between the phenotypes of its homozygous parents. Incomplete dominance – one allele (gene) is not completely dominant over another resulting in a blending of traits and where the phenotype of a hybrid
displays a blending of the two alleles. Codominance – both dominant alleles (genes) in an individual are expressed as in blood types. Codominance-Closely related to incomplete dominance is codominance, in which both alleles are simultaneously expressed in the heterozygote.We can see an example of codominance in the
MN blood groups of humans (less famous than the ABO blood groups, but still important!). A person's MN blood type is determined by his or her alleles of a certain gene. In both codominance and incomplete dominance, both alleles for a trait are dominant. Gene regulation most often happens at the level of
transcription, via transcription factors.GENE EXPRESSION-Transcription and Translation utilize the DNA template code to ultimately produce proteins. Many factors control gene expression including: factors affecting DNA structure, gene expression, factors affecting assembly of proteins after translation, hormones,
environmental factors such as viruses.The functional products of most known genes are proteins, or, more accurately, polypeptides. Polypeptide is just another word for a chain of amino acids. Although many proteins consist of a single polypeptide, some are made up of multiple polypeptides. Genes that specify polypeptides are
called protein-coding genes. Not all genes specify polypeptides. Instead, some provide instructions to build functional RNA molecules, such as the transfer RNAs and ribosomal RNAsthat play roles in translation. How does the DNA sequence of a gene specify a particular protein? : Many genes provide instructions for
building polypeptides. How, exactly, does DNA direct the construction of a polypeptide? This process involves two major steps: transcription and translation. Thus, during expression of a protein-coding gene, information flows from DNA→RNA→protein. This directional flow of information is known as the central
dogma of molecular biology. Non-protein-coding genes (genes that specify functional RNAs) are still transcribed to produce an RNA, but this RNA is not translated into a polypeptide. For either type of gene, the process of going from DNA to a functional product is known as gene expression. The study of gene expression is
epigenetics. Most genes contain the information required to make proteins. The journey from gene to protein is one that is complex and controlled within each cell and it consists of two major steps – transcription and translation. Together, these two steps are known as gene expression.A pedigree is a diagram of a family tree
showing the relationships between individuals together with relevant facts about their medical histories.A pedigree analysis is the interpretation of this data that allows a better understanding of the transmission of genes within the familyAutosomal Dominant Inheritance-Trait should not skip generations (unless
penetrance),An affected person married to a "normal" person should have approximately 50% of the offspring being affected. (Also indicates that the affected individual is heterozygous),Distribution of the trait should be close to equal distribution among the sexes. Autosomal Recessive Inheritance-Trait often skips
generations,Distribution of the trait should be close to equal distribution among the sexes,Traits are often found in pedigrees with consanguineous marriages,If both of the parents are affected, all of the children should be affected,Most affected individuals have "normal" parents,When a "normal" person is married to an affected
individual, all of the children are normal (indicating the normal parent is homozygous dominant),If a "normal" person is married to an affected individual and one or more of the children is affected, then approximately half of the children should be affected. (Showing that the "normal" parent is heterozygous). Sex linked Dominant
Inheritance-Trait should not skip generations (unless penetrance),Affected males must come from affected mothers,Approximately half of the children of an affected female are affected. (Figuring the mother is heterozygous),All the daughters, but none of the sons of an affected father are affected,For a female child to be affected,
the father or the mother must be affected. Sex linked Recessive Inheritance-Most of the affected individuals are males,For a female child to be affected, the father must be affected and the mother must be affected or a carrier,All of the sons of an affected mother must be affected,For a male child to be affected, the mother
must be affected or a carrier. (Many times this can be determined by studying males in the mother's family line),Approximately half of the sons of carrier females should be affected.Autosomal Diseases - Cystic Fibrosis is caused by a mutation in the gene cystic fibrosis transmembrane conductance regulator (CFTR). The most
common mutation, ΔF508, is a deletion (Δ signifying deletion) of three nucleotides that results in a loss of the amino acid phenylalanine (F) at the 508th position on the protein. It is an autosomal recessive disorder that is inherited when an individual receives a mutated copy of the gene associated with cystic fibrosis from
both parents. Huntington's disease is an autosomal dominant disorder. Mutations in the HTT gene cause Huntington disease. The HTT gene provides instructions for making a protein called huntingtin.We also make three simplifying assumptions:Complete Penetrance: An individual in the pedigree will be affected
(express the phenotype associated with a trait) when the individual carries at least one dominant allele of a dominant trait, or two recessive alleles of a recessive a trait.Rare-in-Population: In each problem, the trait in question is rare in the general population. Assume for the purposes of these problems that individuals who marry
into the pedigree in the second and third generations are not carriers. This does not apply to the founding parents – either or both of the individuals at the top of the pedigree could be carriers.Not-Y-Linked: The causative genes in these problems may be autosomal or X-Linked, but are not Y-linked.5 Key Clues: There are five
things to remember in reasoning about pedigrees.An unaffected individual cannot have any alleles of a dominant trait: (because a single allele of a dominant trait causes an individual to be affected).Individuals marrying into the family are assumed to have no disease alleles: they will never be affected and can
never be carriers of a recessive trait. (because the trait is rare in the population).An unaffected individual can be a carrier (have one allele) of a recessive trait. (because two alleles of a recessive trait are required for an individual to be affected).When a trait is X-linked, a single recessive allele is sufficient for a male to be
affected. (because the male is hemizygous – he only has one allele of an X-linked trait).A father transmits his allele of X-linked genes to his daughters, but not his sons. A mother transmits an allele of X-linked genes to both her daughters and her sons.Key Patterns in Pedigree Analysis Patterns that Indicate a RECESSIVE Trait:The
disease must be RECESSIVE if any affected individual has 2 unaffected parents. Since this is a genetic disease at least one parent must have an allele for the disease. If neither parent is affected, the trait cannot be dominant.AUTOSOMAL RECESSIVE: If any affected founding daughter has 2 unaffected parents the disease must
be autosomal recessive.An affected individual must inherit a recessive allele from both parents, so both parents must have an allele.If the father had a recessive X-linked allele, he would have to be affected (since he only has one X-linked allele).RECESSIVE: If an affected founding son has 2 unaffected parents, we cannot determine
if the recessive disease is autosomal or x-linked.If the trait is autosomal, both parents can be unaffected carriers of the disease.If the trait is x-linked, the son must have inherited his allele from his mother only, and his father can be unaffected.X-LINKED RECESSIVE: When an affected non-founding son has 2 unaffected parents
the disease must be X-linked recessive.The father, who is marrying in, does not have any disease alleles, since he is marrying into the family;so the affected son inherits an allele only from his unaffected mother.A male cannot be affected by a single autosomal recessive allele, but can be affected by a single X-linked recessive
allele.Patterns that Indicate a DOMINANT Trait-The disease must be DOMINANT if every affected child of NON-FOUNDING parents has an affected parent: The unaffected mother, who is marrying in, does not carry an allele for the disease; so the affected child inherits an allele only from the affected father. No
child could be affected by a single autosomal recessive allele, or X-linked recessive allele, so the trait is dominant.When an affected son of non-founding parents has an affected father the disease must beAUTOSOMAL DOMINANT. A father does not transmit X-linked alleles to a son, so the disease cannot be X-linked
dominant.When an affected daughter of non-founding parents has an affected father, we cannot determine whether the DOMINANT disease is autosomal or x-linked. The affected father can transmit either an autosomal dominant allele, or an X-linked dominant allele to his daughter.Determining Autosomal
Inheritance-Dominant and recessive disease conditions may be identified only if certain patterns occur (otherwise it cannot be confirmed)Autosomal Dominan-If both parents are affected and an offspring is unaffected, the trait must be dominant (parents are both heterozygous),All affected individuals must have at least one
affected parent,If both parents are unaffected, all offspring must be unaffected (homozygous recessive)Autosomal Recessive-If both parents are unaffected and an offspring is affected, the trait must be recessive (parents are heterozygous carriers),If both parents show a trait, all offspring must also exhibit the trait
(homozygous recessive).Determining X-Linked Inheritance-It is not possible to confirm sex linkage from pedigree charts, as autosomal traits could potentially generate the same results,However certain trends can be used to confirm that a trait is not X-linked dominant or recessive.X-linked Dominant-If a male shows a trait,
so too must all daughters as well as his mother,An unaffected mother cannot have affected sons (or an affected father),X-linked dominant traits tend to be more common in females (this is not sufficient evidence though).X-linked Recessive-If a female shows a trait, so too must all sons as well as her father,An unaffected
mother can have affected sons if she is a carrier (heterozygous),X-linked recessive traits tend to be more common in males (this is not sufficient evidence though).Mutations - changes in genetic code of genes or chromosomes and causes. Causes of mutations – chemicals, radiation, temperature. Exons– genes (5%) and Introns
– between genes (95%.). Gene – section of DNA which carries the blueprint for making a protein or part of a protein.A nonsense mutation is a change in one DNA base pair. Instead of substituting one amino acid for another, however, the altered DNA sequence prematurely signals the cell to stop building a
protein.Stop codons - If a change in the DNA sequence, or mutation, of a gene occurs that creates a stop codon, this is called a nonsense mutation.–of UAA, UAG, UGA are formed by the DNA coding strand at ATT, ATC, ACT · The three base code on t RNA is termed an anticodon because it will bond to a m-RNA codon during
translation or protein synthesis.There are many types of chromosome abnormalities. However, they can be organized into two basic groups: numerical abnormalities and structural abnormalities.Numerical Abnormalities: When an individual is missing one of the chromosomes from a pair, the condition is called
monosomy. When an individual has more than two chromosomes instead of a pair, the condition is called trisomy.An example of a condition caused by numerical abnormalities is Down syndrome, which is marked by mental retardation, learning difficulties, a characteristic facial appearance and poor muscle tone (hypotonia) in
infancy. An individual with Down syndrome has three copies of chromosome 21 rather than two; for that reason, the condition is also known as Trisomy 21. An example of monosomy, in which an individual lacks a chromosome, is Turner syndrome. In Turner syndrome, a female is born with only one sex chromosome, an X, and is
usually shorter than average and unable to have children, among other difficulties.Structural Abnormalities: A chromosome's structure can be altered in several ways.Deletions: A portion of the chromosome is missing or deleted.Duplications: A portion of the chromosome is duplicated, resulting in extra genetic
material.Translocations: A portion of one chromosome is transferred to another chromosome. There are two main types of translocation. In a reciprocal translocation, segments from two different chromosomes have been exchanged. In a Robertsonian translocation, an entire chromosome has attached to another at the
centromere.Inversions: A portion of the chromosome has broken off, turned upside down, and reattached. As a result, the genetic material is inverted. The difference between deletion and insertion is that deletion is (genetics) a mutation in which a gene, or other section of dna, is removed from a chromosome while
insertion is (genetics) the addition of a nucleotide to a chromosome by mutation. Uniparental disomy is when two copies of a chromosome are inherited from one parent, and no chromosome is inherited from the other parent.Monogenic disease is a genetic disease caused by a change in one gene.Gregor Mendel is the
father of both genetics and heredity.When traits are passed from one generation to another they follow principles of genetic inheritance that were first defined by Gregor Mendel, a monk and scientist who worked in the mid-nineteenth century. Mendel's studies yielded three "laws" of inheritance: the law of dominance, the law
of segregation, and the law of independent assortment. Each of these can be understood through examining the process of meiosis.The Law of Dominance-A dominant trait is a trait whose appearance will always be seen in offspring. In other words, dominance describes the relationship between two alleles. If an individual
inherits two different alleles from each of its two parents and the phenotype of only one allele is visible in the offspring, then that allele is said to be dominant. Mendel's law of dominance states that if one parent has two copies of allele A -- the dominant allele -- and the second parent has two copies of allele a-- the recessive allele
-- then the offspring will inherit an Aa genotype and display the dominant phenotype.The Law of Segregation-A parent may have two distinct alleles for a certain gene, each on one copy of a given chromosome. Mendel's second law, the law of segregation, states that these two alleles will be separated from each other during
meiosis. Specifically, in the second of the two cell divisions of meiosis the two copies of each chromosome will be separated from each other, causing the two distinct alleles located on those chromosomes to segregate from one another. Mendel's law (also called the law of segregation) states that during the formation of
reproductive cells (gametes), pairs of hereditary factors (genes) for a specific trait separate so that offspring receive one factor from each parent.The Law of Independent Assortment-Mendel's third law, the law of independent assortment, states that the way an allele pair gets segregated into two daughter cells during the
second division of meiosis has no effect on how any other allele pair gets segregated. In other words, the traits inherited through one gene will be inherited independently of the traits inherited through another gene because the genes reside on different chromosomes that are independently assorted into daughter cells during
meiosis.Mendel worked with seven characteristics of pea plants: plant height, pod shape and color, seed shape and color, and flower position and color. Mendel’s four postulates and laws of inheritance are: (1) Principles of Paired Factors (2) Principle of Dominance(3) Law of Segregation or Law of Purity of Gametes
(Mendel’s First Law of Inheritance) and (4) Law of Independent Assortment (Mendel’s Second Law of Inheritance).23 chromosomes are inherited from your father from a sperm cell called a gamete. Gametes contain half of the number of chromosomes as body cells. Sperm cells are considered haploid cells because they
only contain 1 set of chromosomes. The other 23 chromosomes come from your mother, from an egg cell which is also a gamete. Is also haploid. When the sperm and egg cell combine they form a fertilized egg called a zygote. The resulting cell is a diploid because it contains 2 sets of chromosomes.Karyotypes are
the number and types of chromosomes in a eukaryotic cell – they are determined via a process that involves: Harvesting cells (usually from a foetus or white blood cells of adults),Chemically inducing cell division, then arresting mitosis while the chromosomes are condensed,The stage during which mitosis is halted will
determine whether chromosomes appear with sister chromatids or not. Sometimes, babies have an extra chromosome, a missing chromosome, or an abnormal chromosome. Chromosomes are made up of chromatin and chromatin contains DNA and protein.Dna is wound around protein called histones forming
nucleosomes.Karyotypes can be used for many purposes; such as to study chromosomal aberrations, cellular function, taxonomic relationships, and to gather information about past evolutionary events.A Karyogram is a way used to depict chromosomes, the way chromosomes are organised in the image makes them easy to
visualize. They are arranged into homologous pairs each of which is arranged into size order- from largest to smallest.However, chromosome 21 is actually shorter than chromosome 22.This was discovered by genome sequencing.This was discovered after the naming of Down syndrome as trisomy 21,
reflecting how this disease results from possessing one extra chromosome 21 (three total). Not wanting to change the name of this important disease, chromosome 21 retained its numbering, despite describing the shortest set of chromosomes. The chromosome “arms' ' projecting from either end of the centromere may be
designated as short or long, depending on their relative lengths. Each chromosome has a centromere (CEN), region which contains the kinetochore, a microtubule organising centre (MTOC) responsible for attachment of the chromosome to the spindle apparatus at mitosis. The 2 sister-chromatids are principally held
together at the para-centric heterochromatin at opposite ends of the centromeric region.CEN divides the chromosome into two arms.Giemsa banding (G-banding) is the standard technique used to identify individual chromosomes by producing characteristic light and dark bands. Giemsa banding involves the treatment of
the cells on the slides with trypsin followed by Giemsa stain. Chromosomes are classified by the position of the centromere in relation to the chromosome. The short arm is abbreviated p (for “petite”), whereas the long arm is abbreviated q (because it follows “p” alphabetically).An ideogram is a chromosome map
which describes specific regions of each of the chromosomes. The most common form of Karyogram shows photographs of chromosomes, the photographs are taken during meiosis specifically metaphase at which point chromosomes are condensed and become visible where they would otherwise not be seen as discrete
entities.Karyotyping will typically occur prenatally and is used to:Determine the gender of the unborn child (via identification of the sex chromosomes) and Test for chromosomal abnormalities (e.g. aneuploidies or translocations). Cytogenetics is the study of chromosomes and their structure, inheritance, and
abnormalities..Rings: A portion of a chromosome has broken off and formed a circle or ring. This can happen with or without loss of genetic material.Most chromosome abnormalities occur as an accident in the egg or sperm. In these cases, the abnormality is present in every cell of the body. Some abnormalities, however,
happen after conception; then some cells have the abnormality and some do not.Chromosome abnormalities can be inherited from a parent (such as a translocation) or be "de novo" (new to the individual). This is why, when a child is found to have an abnormality, chromosome studies are often performed on the parents.Bacteria
chromosomes are circular. This is why they lack telomerase.The DNA molecules found in mitochondria and chloroplasts are small and circular, much like the DNA of a typical bacterium. There are usually many copies of DNA in a single mitochondria or chloroplasts.A submetacentric chromosome is a chromosome
whose centromere is located near the middle. As a result, the chromosomal arms (i.e. p and q arms) are slightly unequal in length and may also form an L-shape. A chromosome with equal chromosomal arms is termed metacentric chromosome.Acrocentric: centromere is almost at the end of the
chromosome.Telocentric: centromere is at the end of the chromosome.Gamete Formation · Spermatogenesis – 4 mature sperm cells from meiosis. · Oogenesis – 1 egg and 3 polar bodies..The chromosome number is the same in the daughter cells as it was in the parent cell. Because DNA is duplicated during interphase
before the cell undergoes mitosis, the amount of DNA in the original parent cell and the daughter cells are exactly the same. Exons are coding areas whereas introns are non-coding areas. An exon is termed as a nucleic acid sequence which is represented in theRNA molecule. Introns are termed as nucleotide sequences seen
within the genes which are removed through RNA splicing for generating a mature RNA molecule. Introns are used to regulate gene expression, it is noncoding DNA, and there are more introns than exons. Gamete refers to a haploid sex cell that is a sperm in males and egg (oocyte) in females. Zygote is the diploid cell that
results from the fertilization between an egg and a sperm.There are 46 chromosomes in a zygote. In mammals, the sperm (male gamete) fertilizes the egg (ovum, the female gamete) and the fertilized egg is called a zygote. Most DNA is located in the cell nucleus (where it is called nuclear DNA), but a small amount of
DNA can also be found in the mitochondria (where it is called mitochondrial DNA or mtDNA). Mitotic nondisjunction can occur with the inactivation of either topoisomerase II, condensin, or separase. This will result in 2 diploid daughter cells, one with 2n+1 and the other with 2n-1. The ensemble of formations and
folds in a single linear chain of amino acids — sometimes called a polypeptide — constitutes the tertiary structure of a protein. The tight pairing of homologous chromosomes is called synapsis.These paired up chromosomes—two from each parent—are called tetrads.The point the points of contact, the physical link
between two (non-sister) chromatids belonging to homologous chromosomes is the chiasmata. A chiasma is the point of contact, the physical link, between two chromatids belonging to homologous chromosomes.Homologous (similar) chromosomes from both parents pair up and may exchange DNA in a process known as
crossing over. This results in genetic diversity.In metaphase 1, some of the spindle fibers attach to the chromosomes' centromeres.The fibers pull the tetrads into a vertical line along the center of the cell.Anaphase 1 is when the tetrads are pulled apart from each other, with half the pairs going to one side of the cell and the
other half going to the opposite side. It is important to understand that whole chromosomes are moving in this process, not chromatids, as is the case in mitosis.At some point between the end of anaphase 1 and the developments of telophase 1, cytokinesis begins splitting the cell into two daughter cells.In telophase 1, the spindle
apparatus dissolves, and nuclear membranes develop around the chromosomes that are now found at opposite sides of the parent cell / new cells.Heterochromatin: is a part of chromosome, a tightly packed form of DNA whereas euchromatin is an uncoiled form of chromatin; has tighter DNA packing than euchromatin;
stains dark in interphase whereas euchromatin stains lightly with basic dyes but stains dark during mitosis, when it is in condensed state during each repetition of the cell cycle; contains more DNA compared to euchromatin; found in eukaryotes whereas euchromatin found in both eukaryotes and prokaryotes; is genetically
inactive and euchromatin is genetically active; is late replicative whereas euchromatin is early replicative.Central dogma of molecular genetics is DNA -‡RNA -‡Protein.Exceptions among viruses – RNA to DNA (retroviruses) - Exception is in retroviruses where genetic storage vehicle is RNA. It then makes a DNA which
replicates to form double stranded DNA and continues through dogma.Hemizygous is a condition in which only one copy of a gene or DNA sequence is present in diploid cells.Males are hemizygous for most genes on sex chromosones, having only one X and one Y chromosone.The number of DNA molecules can roughly
double in each round of cycling.Gametogenesis is the process that forms gametes for sexual reproduction. Meiosis is required for gametogenesis. The key difference between meiosis and gametogenesis is, meiosis is a cell division process while gametogenesis is a process of gamete formation.Anatomy of the
mitotic spindle- kinetochore microtubules (bound to kinetochores) and the aster. The aster is an array of microtubules that radiates out from the centrosome towards the cell edge. Diagram also indicates the centromere region of a chromosome, the narrow "waist" where the two sister chromatids are most tightly connected, and
the kinetochore, a pad of proteins found at the centromere. The centromere is the specialized DNA sequence of a chromosome that links a pair of sister chromatids.Microtubules can bind to chromosomes at the kinetochore, a patch of protein found on the centromere of each sister chromatid. (Centromeres are the regions of
DNA where the sister chromatids are most tightly connected.) Microtubules that bind a chromosome are called kinetochore microtubules. Microtubules that don’t bind to kinetochores can grab on to microtubules from the opposite pole, stabilizing the spindle. More microtubules extend from each centrosome towards the edge of
the cell, forming a structure called the aster.To prevent the loss of genes as chromosome ends wear down, the tips of eukaryotic chromosomes have specialized DNA “caps” called telomeres. Telomeres consist of hundreds or thousands of repeats of the same short DNA sequence.Gametes contain half the chromosomes
contained in normal diploid cells of the body, which are also known as somatic cells. Somatic cells are body cells that are not sperm or egg cells. Somatic cells of a human have 46 chromosomes and are considered diploid. Haploid gametes are produced during meiosis, which is a type of cell division that reduces the
number of chromosomes in a parent diploid cell by half. Robertsonian translocation is when 2 non-homologous chromatids bond.Linkage – genes on the same chromosome are inherited as a group. Autosomal linkage – on autosomes. Sex-linked – on sex chromosomes. Epistasis - the interaction between two or
more genes to control a single phenotype so one pair of genes alters the expression of another pair of genes as albino. Multifactorial inheritance - many factors (multifactorial) both genetic and environmental are involved in producing the trait or condition. Examples: height, weight, cleft palate, spina bifida. The sense strand
has the information that would be readable on the RNA, and that's called the coding side. The antisense is the non-coding strand, but ironically, when you're making RNA, the proteins that are involved in making RNA read the antisense strand in order to create a sense strand for the mRNAThe SRY
gene is the gene that produces the Y chromosome, therefore it helps produce testosterone, the hormone found in males.Glossary - kinetochore-the portion of chromosome centromere to which the mitotic spindle fibers attach.centromere-a specialized constricted region of a chromatid; contains the kinetochore. In cells a
prophase and metaphase, sister chromatids are joined in the vicinity of their centromeres.gene - a unit of inheritance that usually is directly responsible for one trait or character. Each individual has two genes for each trait, one comes from dad and the other from mom. Allele - alternate forms of a gene. Usually there are two
alleles for every gene, sometimes there are more than two alleles present in population – termed multiple alleles.homozygous - when the two alleles are the same.heterozygous - when the two alleles are different.dominant - a trait (allele) that is expressed irregardless of the second allele.recessive - a trait that is only
expressed when the second allele is the same (e.g. short plants are homozygous for the recessive allele).punnett square - probability diagram illustrating the possible offspring of a mating male genes on top of columns and female traits on side of rows.phenotype - the physical expression of the genes for the trait by an
individual.genotype - the gene makeup of an organism. Phenotype is the trait an individual expresses while genotype is the two genes that cause that trait.Monohybrid Cross – a cross involving only one trait. hybrid – an individual who has one dominant and one recessive gene for a trait.Dihybrid Cross – a cross involving
two traits.Incomplete dominance – one allele (gene) is not completely dominant over another resulting in a blending of traits and where the phenotype of a hybrid displays a blending of the two alleles.Codominance – both dominant alleles (genes) in an individual are expressed as in blood types.Blood types – A,B,O alleles A
and B genes are co-dominant and both dominant over the O gene which is recessive.Independent Assortment – genes on different chromosomes separate independently during meiosis.X-linked traits more common in men.sex-linkage – allele (gene) is located on a sex chromosome and it will be more common in one sex. It
is usually on the x-chromosome and more common in males than in females. Barr bodies – tightly coiled X chromosome in females – inactive X chromosome. Calico cats – usually on females. yellow and black alleles on X chromosome - female has 2 X’s. Probability – ratios or percentages.Multiple Alleles – three or more
alleles for a gene as blood type as skin color.Multifactorial Traits – more than 1 pair of genes plus environment.Pleiotropy – the action of an allele (gene) affects many parts of the body as sickle cell anemia.Variable expressivity – an allele (gene) can be expressed differently in different people. Epistasis - the interaction
between two or more genes to control a single phenotype so one pair of genes alters the expression of another pair of genes as albino.Pedigree Analysis-Pedigree is a family tree.Squares are males and circles are females. Generations = I – Original Parents. II- F1 (children. III – F2 (grandchildren).Karyotype Analysis karyotype is a print of human chromosomes.nondisjunction – chromosomes do not separate during meiosis. Results in monosomy and trisomy.Karyotype Characteristics: The numbered chromosome pairs termed autosomes are arranged longest to shortest,Chromosomes come in pairs,The sex (X & Y) chromosomes are
placed last with normal females having XX and normal males having XY,If only X chromosomes are present, it will be female,If X and Y chromosomes are present, it will be male,Bent chromosomes are not abnormal,It is just the way they were photographed,If an individual has an extra chromosome, it is termed trisomy and if a
chromosome is missing, it is termed monosomy.chromosomes-threadlike structures made of DNA molecules that contain the genes.Sexual reproduction-type of reproduction in which two organisms each contribute half of their genes to produce a new offspring.The new offspring has a unique set of genes. Sexual
reproduction is importanat because there is greater ginetic diversity between species.Asexual reproduction:type of reproduction in which one organism produces a genetic copy of itself.Purebred-The offspring of many generations that have the same traits Regions of Chromosome for Replication-Difference between
heterochromatin and euchromatin-Heterochromatin is a part of chromosome, a tightly packed form of DNA whereas euchromatin is an uncoiled form of chromatin.Heterochromatin has tighter DNA packing than euchromatin.Heterochromatin stains dark in interphase whereas euchromatin stains lightly with basic dyes but
stains dark during mitosis, when it is in condensed state during each repetition of the cell cycle.Heterochromatin contains more DNA compared to euchromatin.Heterochromatin found in eukaryotes whereas euchromatin found in both eukaryotes and prokaryotes.Heterochromatin is genetically inactive and euchromatin is
genetically active.Heterochromatin is late replicative whereas euchromatin is early replicative.Gamete- a mature haploid male or female germ cell which is able to unite with another of the opposite sex in sexual reproduction to form a zygote. Genetic diversity is the total number of genetic characteristics in the genetic
makeup of a species. It is distinguished from genetic variability, which describes the tendency of genetic characteristics to vary. Genetic diversity serves as a way for populations to adapt to changing environments. Cancer cells have the ability to replicate at a very high rate. Some types of cancer cells are able to do this
because they produce an enzyme called telomerase,which adds additional telomeres to their DNA. Telomeres are protective DNA on the ends of chromosomes to prevent the necessary part of DNA from getting shorter when the cell divides. During methylation a methyl group is attached to a gene, causing it to not be expressed.