exam 3 genetics

somatic mutations

• mutations occurring in somatic cells during development, or in adulthood

• not inherited bc not in germ line

germline mutations

• mutations that occur in the cell lineage that is destined to become the gametes

• give rise to heritable genetic disorders

• phenylketonuria (PKU)-mutation in phenylalanine hydroxylase

  • phyenylalanine broken down into metabolites that affect myeline formation leading to mental retardation. 1:8000 births

fragile X syndrome

• typical individual has approx 30 CGG repeats

• critical number appears to be greater than 50

• then gets rapid accumulation with subsequent generations

• can reach 230 or more copies

• repeats only expand in female germline

importance of mutations

• one of the major processes that contribute to genetic variation

• genetic variation provides the raw material for evolution

• genetic analysis would not be possible without mutations causing variation within individual genes.

2 classes of genetic mutations

1) mutations affecting single base pairs of DNA

2) mutations altering the # of copies of genes

nonsense mutations

• codon for one amino acid is changed into a translation termination

• leads to a truncated protein

frameshift mutation

• insertion or deletion of one or more nucleotides

• results in a change of the translational reading frame

epigenetic

• histone modification and DNA methylation (epigenetic marks) can be inherited by daughter cells

• diet, envirnoment, and disease can alter epigenetic marks

• basis of imprinting and epigenetic inheritance

imprinting

• insulin like growth factor 2

  • expressed allele inherited from the paternal side

• H19

  • expressed allele inherited from materal side

epigenetics

DNA methylation across generations

agouti gene

encode a protein that controls production of pigment in hair follicles

• wild type agouti expression — mixture of yellow and black

• dominant mutant agouti — mutation causes ectopic expression

mother fed control diet

yellowy and big

mother fed dirt with added folate (methyl-donor)

brown and small

hardy-weinberg equilibrium

P² + 2PQ + Q²=1

P

frequency of A allele

Q

frequency of a allele

2PQ

frequency of heterozygote

population genetics

relates process of an individuals genotype to the genetic composition of populations and to changes in that composition over time and space

causes of changes —population genetics

mutation, migrations btwn populations, assortative mating btwn different or similar phenotypes, recombination generating new combinations, genetic drift (random sampling of gametes), natural selection

genotype frequences

• observed proportions of genotypes in a population

• many genes are polymorphic

  • multiple alleles present in a population or between different populations

• allele frequency refers to the frequency of a specific allele in the population

hardy-weinberg equilibrium

• sexual reproduction maintains constant genetic variation from generation to generation

• unless there are events that drive the frequency of a given gene out of equilibrium

heterozygosity

• measure of genetic variation is the amount of heterozygosity for a gene in a population

• total frequency of heterozygotes

inbreeding

mating between individuals with common ancestry

positive assortative mating

mating between individuals with similar phenotypes (race, height)

introgression from neandertals

• multiple genes involved in regulating circadian rhythm

• multiple genes controlling innate immune response to virus infection

introgression