GENETICS
Genetics – branch of biology that studies the process of heredity
Gregor Mendel (1822-1884) – “father of genetics” Austrian monk who performed experiments on the
inheritance of the pea plant. He said that inherited characteristics are carried by discrete units which later
became known as genes.
The genes exist at definite loci (permanent locations) on chromosomes.
I. Heredity and Genes – When two organisms reproduce, their offspring receive genetic instructions, called
genes, from each parent. The genes determine which traits or characteristics, each offspring will have.
A. Heredity – passing of genetic information (DNA) from one generation to another through
reproduction
DNA – deoxyribonucleic acid
1. DNA is found in genes which are found in chromosomes which are found in nuclei which are
found in cells.
Chromosomes have hundreds, sometimes thousands of genes in them.
2. Traits inherited by an individual can be determined by one pair of genes or by several pairs of
genes.
3. Allele – alternate forms of the genes (the actual information contained in the gene)
Ex) Pea plants – color: seeds can be green or yellow
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II.
Methods of Reproduction
A. Asexual Reproduction – involves one parent (often a single-celled organism)
- offspring are usually identical to the parent
- identical genetic copies are known as clones
ex) bacteria, ameba, yeast
B. Sexual Reproduction – involves two parents
- sperm produced by the male fuses (joins) with egg from female
- each sex cell contains only one gene from each pair
- Therefore, offspring receives half of its genetic info. from the female parent by way of the egg
and half from the male parent by way of the sperm
1. Genetic Recombination – when sperm and egg combine to form a zygote, the resulting genes
are a combination of both parents.
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III.
This way, offspring may resemble either or both parents but will NOT be identical to either one
of them.
Genetic Code – the inherited instructions (genes) that are passed from parent to offspring exist in the
form of a chemical code. This code is contained in DNA molecules of ALL organisms.
A. DNA Structure – 1953 - proposed by Watson & Crick; shape is a double helix
made up of nucleotides which have 3 subunits: sugar, phosphate, nitrogen base
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the bases are represented by 4 letters: A,T,C,G
A = Adenine T = Thymine C = Cytosine G = Guanine
A always pairs with T /
C always pairs with G
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IV.
DNA Replication – nitrogen bases of DNA are connected by weak, hydrogen bonds. DNA separates
(unzips) at these bonds to form two single strands.
- each single strand becomes a template, or pattern, for a new molecule
- Replication produces two identical copies of the cell’s genetic information, each ready to be
passed from the parent cell to two daughter (offspring) cells.
V.
Proteins and Cell Functioning – Proteins are made up of 20 different kind of amino acids. The
sequence of amino acids in a particular protein influences the shape of the molecule, since some of the
amino acid parts are attracted to other amino acid parts of the chain. The connections that form between
different parts of the chain cause it to fold and bend in a specific way. The final folded shape of the
protein enables it to carry out its function in the cell.
Ex) enzymes, hormones, antibodies, antigens
VI.
Gene Control of Cellular Activities – the control of cellular activities involves both DNA & RNA
- DNA provides the information needed by the cells to produce enzymes needed for all activities.
- RNA carries this information from the nucleus to the ribosomes and helps in protein synthesis
A. RNA (Ribonucleic acid) – like DNA, is composed of nucleotides 3 differences:
DNA’s sugar is deoxyribose
DNA has thymine (T)
DNA has 2 chains
RNA’s sugar is ribose
RNA has uracil (U)
RNA has one chain
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3 types of RNA: mRNA, tRNA, rRNA
Messenger RNA (mRNA) – “carries” the DNA message from the DNA in the nucleus to the
sites of protein synthesis in the cytoplasm (ribosomes)
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Transfer RNA (tRNA) – “transfers” amino acids within the cytoplasm to the ribosomes
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Ribosomal RNA (rRNA) – mRNA codes are read and translated
Evidence strongly suggests that a genetic code exists. This code contains the information for the
sequence of amino acids in a particular protein. The RNA code is a triplet code (codon) made up of 3
nitrogen bases complementary to various sequences of three bases in the DNA molecules.
Ex) CTT AGC TAA
GAA UCG AUU
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VII.
Protein Synthesis – DNA serves as a template for the synthesis of proteins
- mRNA molecules carry specific code from DNA in nucleus to cytoplasm
- tRNA molecules arranged as anticodons pick up and transfer amino acids to the ribosomes
- tRNA molecules bond to codons of mRNA molecules and specific protein chains are formed
VIII. Interaction of Heredity and Environment – the environment interacts with genes in the development
and the expression of inherited traits.
Ex) plants – effect of light on chlorophyll production: no light, most plants turn yellow. In presence of
light, plant will develop chlorophyll and turn green
IX.
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effect of temperature on hair color in the Himalayan rabbit – normal Arctic environment, hair is
white with black on extremities. In warm climate, all of their hair is white.
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identical twins can have changes in their physical appearances (phenotype) that are dependent on
the environment
Mutations – any change in the DNA sequence. They are random and can occur anywhere along the
molecule. Caused by such things as chemicals & radiation
Ex) substitution, deletion, addition, inversion
Mutagens (mutagenic agents) – Anything that causes a mutation
1. Radiation- ultraviolet light, x-rays, radioactive substances.
2. Chemicals- asbestos fibers, tobacco
** Only mutations found in sex cells can be inherited by the offspring.
Body cell mutations are not passed on to offspring; they can be passed on to other body cells only.
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X. Genetic Engineering – new technology that humans use to alter the genetic instructions in organisms
A. Cloning – process of producing a group of genetically identical offspring from the cells of an
organism
- Benefit – can produce plants and animals with desirable characteristics very rapidly
B. Gene Manipulation – genetic information may be transferred from one organism to another,
resulting in the formation of recombinant DNA
- Enzymes cut DNA segments that allow the segments to be spliced or moved and attached to the
DNA of a new organism
- once in the new organism, the transferred genes direct the new organism’s cells to make the
same protein product as the original organism.
Ex) “genetically engineered” bacteria to produce human growth hormone, interferon, and
insulin, clean up oil spills
** Other enzymes have been found that can be used to make many copies of segments of DNA. These can be
used to increase the amount of DNA available from a tiny sample. This procedure is helpful even when only a
drop of blood or saliva is found at a crime scene. By copying and re-copying the DNA in the sample, criminal
investigators can produce a sample that is large enough to test. The test results may identify or clear suspects.
Uses for Genetic Engineering
1) To improve crop plants  disease resistant, drought resistant, bug resistant, bruise less, produce more fruit
2) To produce safer, cheaper medicines  bacteria producing human insulin and human growth hormone
3) Gene therapy  ex. using genetically altered viruses to deliver “normal” genes into the lung cells of
patients with cystic fibrosis
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XI.
Medical Genetic Research – biological research generates knowledge used to design ways of
diagnosing, preventing, treating, controlling, or curing diseases of plants and animals.
A. Genetic Counseling – discussions between physician and the family which include probabilities of
inheritance patterns, predictions of genetic disorders, and family planning.
1. Amniocentesis – a sample of amniotic fluid is withdrawn from the uterus; cells are cultured and
tested for chromosomal abnormalities; usually done at 14-16_weeks of gestation
2. Screening – the chemical analysis of body fluids such as blood & urine
- Analysis may indicate the presence of chemicals associated with genetically related disorders
3. Karyotyping – preparation of an enlarged photograph showing paired homologous
chromosomes from a cell. May show an extra or missing chromosome
XII.
Human Genetic Disorders - many are rare & difficult to diagnose; Not curable, but treatable when
detected early
A. PKU (Phenylketonuria) – caused by a recessive mutation
1. Nature – enzyme missing to convert phenylalanine to tyrosine
Results: a change in chemical pathways to form toxic chemicals that cause mental retardation.
B. Sickle-Cell Anemia – fatigue, loss of appetite, dehydration; found mainly in African-Americans
1. Nature – sickle-shaped fragile red blood cells; occur when there is a low level of O2 in the body;
sickle cells cause clotting of blood vessels; RBC’s live only 10-25 days and are destroyed faster
than new ones are made
H
H
2. Inheritance of disease:
H = normal hemoglobin
h = abnormal hemoglobin
HH = normal
Hh = carrier
hh = sickle cell disease
H
h
C. Cystic Fibrosis – occurs mainly among northern European whites
Symptoms: thick mucus in lungs
Caused by a recessive allele
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XIII. Selective Breeding
A. Also known as artificial selection including inbreeding & hybridization (cross-breeding) and the
maintenance of desirable mutations by vegetative propagation are methods used by scientists to
improve, produce, and maintain new varieties of animals and plants
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Animals - dogs, cattle, horses
Plants - seedless fruit, hybrid roses, apple varieties
XIV. Applications of Biotechnology – the health care field has much to gain through our increasing
knowledge of genetics and biotechnology
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New methods enable us to locate and decode genes that cause diseases. Once we have a better
understanding of the gene’s specific defect, we may be able to develop ways to treat victims of the
disease. In some cases, we may be able to alter the DNA in affected cells and cure the person.
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