Human Genetics Exam 1

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Domestic plants and animals.

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10,000 BC

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Schleiden and Schwann's cell theory.

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1838

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Charles Darwin published "Origin of the Species".

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1859

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Mendel's pea plant experiements.

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1866

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Miescher isolated DNA

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1866

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Galton studied inherited characteristics, eugenics.

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1880-1900

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Garrod studies inborn errors of metabolism.

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1909

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Beadle and Tatum posit one gene = one enzyme.

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1941

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Avery, Macleod, McCarty posit DNA is genetic material

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1944

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Linus, Pauling discover sickle cell anemia is a molecular disease

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1949

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Watson and Crick publish on the structure of DNA

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1953

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Beginning of genetic engineering.

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1975

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First test tube baby.

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1978

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Bishop , Varmus discover oncogenes.

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1980

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AIDS virus isolated.

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1983

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Francis, Collins -- start of human genome project.

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1988

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Gene replacement therapy begins.

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1990

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Dolly the sheep cloned.

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1996

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Human genome sequence 99% completed.

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2000

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Epigenetic gene expression alteration methods:

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Addition of methyl groups, phosphate, or acetyl groups to DNA or histone proteins.

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Changes that influence the phenotype without altering the genotype:

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Inactivation of one X chromosome on 16th day post fertilization.
Genomic imprinting: DNA is altered by male and female differently during gametogenesis. "Gene expression occurs from only one allele. The expressed allele is dependent upon its parental origin. For example, the gene encoding Insulin-like growth factor 2 (IGF2/Igf2) is only expressed from the allele inherited from the father." Male/female 'code' erased from donated gene, replaced with appropriate sex for donor when encoded into gamete.

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Epigenetics (definition):

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Heritable traits that do not involve changes to the underlying DNA

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Chromatin remodeling:

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Chromatin is the complex of DNA and the histone proteins with which it associates.

Changes in amino acid makeup of histone proteins, addition of methyl groups to DNA (cytosine -> methylcytosine).

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Definition of a gene:

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A segment of DNA containing biological information and coding for an RNA and/or protein or controlling gene expression. The physical and functional unit of heredity.

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Size of a gene (average):

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30,000 nucleotides total. 1,500 functional nucleotides coding for final product RNA or protein.

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Transcription

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DNA -> mRNA

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Translation

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mRNA -> proteins

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Exon

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Area of gene expressed in amino acid sequence.

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Intron

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Area of DNA and RNA not expressed, waste coding.

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Chromosome structure

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Telomere (end cap) - genes - centromere - genes - telomere.

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# of genes per chromosome:

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From 3,000 on #1 to 290 on #22 and 230 on # Y.
X is size of #5 (1,500 genes).

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Molecular Genetics

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Study of DNA structure (genomics) and expression, protein function and variations (proteomics).

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Molecular Medicine

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Matches DNA mutations or abnormal proteins and their functions with diseases.

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Cytogenetics

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Study of chromosomal abnormalities to match gross changes with diseases.

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Transmission/Mendelian Genetics

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Pedigree analysis to determine the characteristics of a single gene as dominant, recessive, sex-linked, or multifactorial (several genes and/or environment).

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Population Genetics

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Study of the allelic frequencies and evolutionary relationships between populations.

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Human DNA size (in BP)

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Total DNA = 3x10^9 (3 billion) base pairs.

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Double helix size:

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3.4 angstroms per base pair = 1.02 meters long, 2nm (20 angstroms) wide.

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Number of genes in humans

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C. 30,000

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Percent of DNA used to code for mRNA

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30%

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Percent of DNA actually used to code for proteins

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1.5%

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Bonds that stabilize DNA:

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1. Hydrogen bonds between strands.
2. Hydrophobic bonds between stacked bases.
3. Phosphodiester bonds (strong, covalent) between sugars.

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Properties (not bonds) that stabilize DNA:

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4. Hydrophobic inside, hydrophilic outside.
5. Mg+ ions around negatively charged DNA.
6. + histone proteins, - DNA (together = chromatin).

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Expressivity

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Degree of expression of a phenotype. Ex. different severities of cystic fibrosis.

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Penetrance

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Percentage of individuals inheriting a genotype who express the corresponding phenotype. (Like 13 if she doesn't get sick from the Huntington's, even though is +.)

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Functions of the Cell Membrane:

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1. Provide attachment to similar cells or signals for migration ("homing").
2. Communication between cells.
3. Receptor for extracellular signals (growth factors, hormones, ligands/signal molecules).
4. Phagocytosis of apoptosed neighboring cells.
5. Secrete products.
6. Surface antigens (cluster designation, human leukocyte antigen).
7. Attachment for microfilaments and tubules.

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Absolute risk of a genetic disease:

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Probability that an individual will develop a particular condition based on family history and/or test results + Punnet square.

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Empiric risk of a genetic disease:

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Probability that a trait will occur based on its incidence in a particular population; 1/100 of a G1P1(downs) mother having a second child with Down's.

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Relative risk of a genetic disease:

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Probability that an individual from a population will develop a particular condition in comparison to another group (usually the general population). 1 is normal/same as population, X<1 = less risk, X>1 = more risk.