Generations = P is parental, F1 is first filial, F2 is second filial
When Mendel crossed two true-breeding parents, he found that all of the offspring were one phenotype. When those offspring were self-pollinated, he found a 3:1 ratio in the F2.
(P) Tall x Short = all Tall (F1)
(F1) Tall x Tall = 3 tall to 1 short (F2)

Figure 14.5
For each character, every organism inherits one allele from each parent.
If the two alleles are different, then the dominant allele will be fully expressed in the offspring, whereas recessive allele will have no noticeable effect on the offspring.

The two alleles separate during meiosis – and gives each offspring a 50% change of getting one of the two alleles =
Mendel’s Law of Segregation. (monohybrid)
Law of independent assortment – (Mendel’s second law) (two traits will be inherited independently from each other) (dihybrid)
Figure 14.6
Homozygous – same alleles, TT, tt
Heterozygous – different alleles Tt
Phenotype – physical expression (tall)
Genotype – genetic make-up (Tt)

Testcross – unknown genotype crossed with a homozygous recessive.
Tall x tt = all Tall (parent was TT)
Tall x tt = half tall, half short (parent was Tt)
Monohybrid cross – one trait
Dihybrid cross – two traits (fork-line)
Rule of multiplication – To calculate the probability that two or more independent events will occur together in a specific combination, multiply the probabilities of each of the independent events.
Problem – what is the probability of getting the genotype
AaBbcc from the parents AABbCc x AaBbCc?
Complete dominance – Tt and TT show the dominant phenotype. tt shows the recessive.
Co-dominance – The dominant and recessive allele both express themselves in their natural form in the heterozygote.
Incomplete dominance – the heterozygote is a blend between the dominant and recessive phenotypes.
Complete Co-dominant Incomplete

BB
Bb bb
Black
Black
White
Black
Black and white
White
Black
Grey
White
Figure 14.10
Multiple alleles – ABO blood system (also co-dominant)
AA, AO = type A
BB, BO = type B
AB = type AB
OO = type O

Figure 14.11
Pleiotrophy – the property of a gene that causes it to have multiple phenotypic effects. For example, sickle-cell anemia has multiple symptoms all due to a single defective gene.
Epistasis – a gene at one locus alters the effects of a gene at another locus. For example, an individual may have genes for heavy skin pigmentation, but if a separate gene that produces the pigment is defective, the gene for pigment deposition will not be expressed. This would lead to a condition called albinism.

Polygenic inheritance – two or more genes have an additive effect on a single phenotype (height, skin color).
Figure 14.13
Pedigrees show relationships between parents and offspring.
Females are circles, and men and squares. Shaded shapes show individuals that express a certain trait.

Figure 14.15
Recessively inherited disorders – require two copies of the defective gene for the disorder to be expressed.

Cystic fibrosis – cell membrane protein – functions in the transport of chloride ions into and out of the cell. The resulting high extracellular levels of chloride cause mucus to be thicker and stickier, leading to organ malfunction and recurrent bacterial infections.
Tay-Sachs – dysfunctional enzyme which is unable to break down certain lipids in the brain. As a result the lipids accumulate in brain cells and the child suffers from blindness, seizures and degeneration of brain function – leading to death.
Sickle-cell disease – mutant hemoglobin molecule forms a sickle shape when oxygen levels are low – clogs small blood vessels, leads to pain, organ damage and even paralysis.
Figure 14.16

Dominant disorders –
Huntington’s disease – degenerative – onset by age 40.
Death in 20 years post diagnosis.
Fetal testing
Amniocentesis – physical removes amniotic fluid around the fetus. Can detect certain disorders.
Chorionic villi sampling – narrow tube is inserted through cervix to get a sample of the placenta with fetal cells.

Figure 14.18
Trait carried on the X or Y in humans. Thomas Hunt
Morgan discovered the existence of sex-linked genes

Females are XX and Males are XY.
Effected fathers pass on their effected gene to their daughters, their sons will get the Y.
Figure 15.7
Duchenne muscular dystrophy – sex-linked disorder – weakening of muscles and loss of coordination. Affected individuals rarely live past their early 20’s.
Hemophilia – blood is unable to clot normally – caused by absence of proteins required for blood clotting.
Linked genes are located on the same chromosome and therefore tend to be inherited together during cell division.
Genetic recombination is the production of offspring with a new combination of genes inherited from the parents.

P Tall, purple x short, white
F1 tall, purple, tall white, short, purple, short white
Parental recombinant recombinant parental
Figure 15.10

Crossing over – explains why some linked genes get separated during meiosis. Linked genes go against the law of independent assortment.
Linkage map – a genetic map that is based on the percentage of cross-over events.
A Map unit is equal to a 1% recombination frequency. Map units are used to express relative distances along the chromosome.
Nondisjunction – unequal division of chromosomes, during meiosis. Results in gametes with too many or not enough chromosomes.

Trisomy – three copies of a chromosome.
Monosomy – one copy of a chromosome
Polyploidy – having more than two complete sets of chromosomes (rare in animals, but frequent in plants)
Down syndrome – Trisomy 21 – characteristic facial features, short stature, heart defects and mental retardation.
Klinefelter syndrome – XXY – sterile, male
Turner syndrome – XO – one sex chromosome, female, sterile.
Mutations:
Deletion – when a chromosomal fragment is lost resulting is a chromosome with missing genes.
Duplication – occurs when the chromosome fragment that broke off becomes attached to its sister chromatid. A zygote will get a double dose of the genes.
Inversion – when a chromosome fragment breaks off and reattaches backwards to its original position.
Translocation – when a deleted chromosome fragment joins a non-homologous chromosome.

Figure 15.15

Alfred Hershey and Martha Chase in 1952 discovered that chromosomes are made up of DNA and protein.
Figure 16.4

Watson and Crick discovered the structure of DNA using
Rosalind Franklin and Maurice Wilkins research in X-ray crystallography (helps to visualize molecules three dimensionally).
Figure 16.6
DNA
1.
Double helix (twisted latter with rigid rungs). The sides or backbone is made up of alternating molecules of sugar and phosphate. The rungs are made up of pair of nitrogenous bases.
2.
The bases are adenine (A), thymine (T), guanine (G), and cytosine (C). A pairs with T, and C pairs with G.

3.
The two sides are antiparallel. 5’ to 3’ on one side and
3’ to 5’ on the other. The number refers to the carbon number on the sugar in the backbone.
Figure 16.5

Figure 16.7

Figure 16.8
DNA to DNA.
The model for DNA Replication is semiconservative which means that each of the daughter molecules is made up of one of the old, parent strands and one new strand.

Figure 16.10
Replication
1.
Replication begins at the origin of replication.
2.
Helicase unwinds the parental double helix forming a replication bubble.

3.
A RNA primer is created at the 5’ end of the leading strand and at each Okazaki fragment of the lagging strand.
4.
DNA replication then proceeds in both directions along the DNA strand until the molecule is copied. DNA polymerase III is used to read the parental strand as a template and add the corresponding DNA nucleotide.
5.
Because the strands of DNA are antiparallel and because replication only move from 5’ to 3’; there is a continuous strand called the leading strand and a strand that is copied in segments called the lagging strand.
6.
DNA polymerase I will remove the DNA nucleotides
(primer) and replace them with DNA.
7.
The lagging strand has segments called Okazaki fragments that will be sealed together by DNA ligase to form one continuous DNA strand.
Figure 16.17

A bacterial chromosome is one double-stranded circular DNA molecule with a small amount of protein.
A eukaryotic chromosome is linear DNA molecules associated with large amounts of protein.
In eukaryotic cells, DNA and proteins are packed together as chromatin. Eukaryotic DNA shows four levels of packaging.
1.
DNA wrapped around proteins called histones. This resembles beads on a string and is called nucleosome.
2.
The string on nucleosomes folds to form a 30 nm fiber.
3.
The folding of the 30nm results in looped domains of
300 nm.
4.
As the looped domains fold, a metaphase chromosome is formed.

Figure 16.21
As DNA becomes highly packaged, it becomes less accessible to transcription enzymes. This reduces gene expression.
One gene codes for a polypeptide, which is either a protein or part of a protein (quaternary structure).

Transcription is the synthesis of mRNA (messenger RNA) using
DNA as a template. It occurs in the nucleus. Only one side of the DNA is used (template strand).
Translation is the production of a polypeptide chain using the mRNA transcript. This occurs at the ribosomes.
A triplet code (codon) has the information for the sequence of amino acids to be hooked together.
Figure 17.3

Figure 17.4
RNA polymerase is an enzyme that separates the two DNA strands and connects the RNA nucleotides and their base-pair along the DNA template strand.
The RNA polymerase can add RNA nucleotides so that mRNA elongates in the 5’-3’ direction. Uracil replaces thymine.

There is a promoter region which is where the RNA polymerase attaches. The end of the gene has a terminator where transcription will stop.
Figure 17.7
1.
Iniation – With the help of transcription factors, RNA polymerase II will bind to the promoter.
2.
Elongation – RNA polymerase moves along the DNA, continuing to untwist the double helix. RNA nucleotides are continually be added.
3.
Termination – after RNA polymerase transcribes a sequence in the DNA, the RNA transcript is released.

In Eukaryotes, a 5’cap and a poly-A tail are added. This helps to facilitate the export of mRNA from the nucleus to the ribosome.
Figure 17.9
Figure 17.10

Figure 17.11
RNA splicing takes out the introns and the exons are sliced together by a splicesome.

There are fewer than 25,000 genes that make approximately
100,000 polypeptides. Alternative RNA splicing allows for different combination of exons, resulting in more than one polypeptide per gene.
tRNA’s function is to transfer amino acids from a pool of amino acids in the cytoplasm to the ribosome. Each tRNA is specific for a particular amino acid based on its anti-codon which will be complementary to the codon on the mRNA.

Figure 17.14
Codon – 3 mRNA bases that code for an amino acid. rRNA complexes with proteins to form the two subunits that form ribosomes. Ribosomes have three binding sites for tRNA
P site – holds the tRNA that carries the growing polypeptide chain.

A site – hold the tRNA that carries the amino acid that will be added to the chain next.
E site – is the exit site for tRNA.
Figure 17.13

Translation:
Initiation – the mRNA binds to the ribosome so that the first codon of the mRNA strand (AUG) is in the proper position.
The corresponding tRNA will match up and bring with it an amino acid. The A site is available and the second tRNA will move in.

Figure 17.5
Elongation – The codon and anti-codon match up in the A site. The amino acid in the P site and A site form a peptide bond. The ribosome moves down the mRNA strand making available the A site.

Termination – a stop codon in the mRNA is reached and translation stops. A protein called release factor binds to the stop codon and the polypeptide is freed from the ribosome.
Polypeptides then fold to assume their specific conformation.
Figure 17.18

Figure 17.21
Base-pair substitution – one nucleotide
Missense mutations – the wrong amino acid is added
Nonsense – translation is stopped.
Insertions – addition of a nucleotide.
Deletion – loss of a nucleotide.
Frameshift – if insertions or deletions are not divisible by three.

Figure 17.23

Figure 17.25

In bacteria, genes are clustered into units called operons.
Operons consist of three parts:
1.
An operator that control the access of RNA polymerase to the genes. The operator is found within the promoter site or between the promoter and the protein coding genes of the operon.
2.
The promoter, which is where RNA polymerase attaches.
3.
The genes of the operon. This is the entire stretch of
DNA required for all the enzymes produced by the operon.

Figure 18.3
Located some distance from the operon is a regulatory gene.
Regulatory genes produce repressor proteins that may bind to the operator site. When a regulatory protein occupies the operator site, RNA polymerase is blocked from the genes of the operon. In this situation the operon is off.
Repressible operons are normally on but can be inhibited.
Inducible operons are normally off but can be activated.

The expression of genes can be turned off and on at any point in the pathway from gene to functional protein. Further, the differences between cell types are not due to different genes being present, but to differential gene expression.

Figure 18.6
The fundamental packaging unit of DNA consists of DNA bound to small proteins termed histones. The more tightly bound DNA is to its histones, the less accessible it is for transcription. This relationship is governed by two chemical interactions:

1 – DNA methylation is the addition of methyl groups to
DNA. It causes the DNA to be more tightly packaged, thus reducing gene expression.
2 – In histone acetylation, acetyl groups are added amino acids of histone proteins, thus making the chromatin less tightly packed and encouraging transcription.
Figure 18.7

Notice that methylation occurs primarily on DNA and reduces gene expression, whereas acetylation occurs on histones and increases gene expression.
Transcription initiation is another important control point in gene expression. At this stage DNA control elements that bind transcription factors (needed to initiate transcription) are involved regulation. Enhancer regions are bound to the promoter region by proteins termed activator and mediator proteins. The resulting transcription initiation complex greatly enhances gene expression.
Figure 18.9

Two types of RNA: micro RNAs (miRNA) and small interfering
RNAs (siRNAs), can bind to mRNA and degrade the mRNA or block its translation.
The zygote undergoes transformation through three interrelated processes.
1.
Cell division is the series of mitotic divisions that increases the number of cells.
2.
Cell differentiation is the process by which cells become specialized in structure and function.
3.
Morphogenesis is the organization of cells into tissues and organs.
What controls differentiation and morphogenesis?
1.
Cytoplasmic determinants are maternal substances in the egg that influence the course of early development. These are distributed unevenly in the early cells of the embryo and result in different effects.
2.
Cell-cell signals results from molecules, such as growth factors, produced by one cell influencing neighboring cells, a process called induction which causes cells to differentiate.

Determination is the series of events that lead to observable differentiation of a cell. Differentiation is caused by cell-cell signals and is irreversible.
Pattern formation sets up the body plan and is a result of cytoplasmic determinants and inductive signals. This is what determines head and tail, left and right, back and forth. Uneven distribution of substances called morphogens plays a role in establishing these axes.
Oncogenes are cancer-causing genes.
Proto-oncogenes are genes that code for proteins that are responsible for normal cell growth. Proto-oncogenes become oncogenes when a mutation occurs that causes an increase in the product of the proto-oncogene, or an increase in the activity of each protein molecule produced by the gene.
Cancer can also be caused by a mutation in a gene whose products normally inhibit cell division. These genes are called tumor-suppressor genes.
An important tumor-suppressor gene is the p53 gene. This gene suppresses cancer in three ways:

1.
The p53 gene halts the cell cycle by binding to cyclindependent kinases. This allows time for DNA to be repaired before the resumption of cell division.
2.
The p53 gene turns on genes directly involved in DNA repair.
3.
When DNA damage is too great to repair, p53 activates suicide genes whose products cause cell death (apoptosis).
The multistep model of cancer development is based on the idea that cancer results from the accumulation of mutations that occur throughout life. The longer we live, the more mutations are accumulated thus the more likely that cancer may develop.