mendel, genetics, & evolutionary mechanisms

gregor mendel

father of modern genetics

three main lessons from pea plant experiments

• inheritance of each trait is determined by discrete “units” or “factors” that are passed on to descendants unchanged

• an individual inherits one unit from each parent for each trait

• a trait may not show up in an individual but can still be passed on to the next generation

particulate inheritance

variants do not blend with each other, remain different particles

law of segregation

traits are inherited as discrete units, recessive masked but preserved

law of independent assortment

alleles are transmitted from parent to offspring independent of other particles

genes vs. alleles

• genes = units

• alleles = variants

DNA

• double helix structure

• A + T, C + G

• 23 chromosome pairs (22 autosomes, 1 gender pair)

• mitochondrial DNA = only maternal

types of genes (4)

• structural = code for tissues

• regulatory = turns genes on/off

• locus = gene location on chromosome

• alleles = 1-20 versions

codominance example

• codominance = both alleles equally dominant, both expressed

• blood types

  • phenotypes: A, B, AB, O

  • genotypes: AO, AA, BO, BB, AB, OO

prokaryotes

no nucleus (bacteria)

eukaryotes

have nucleus (humans)

somatic cells

46 chromosomesg

gametes

23 chromosomes (haploid)

cell division and variation

• mitosis: identical somatic cells

• meiosis: gametes, crossing over, recombination, variation

• haplotypes: linked genes inherited together

4 forces of evolution

• mutation: random DNA base changes, source of new variation, must occur in gametes to matter

• gene flow (migration): movement of genes between populations, increases similarity, reduces speciation

• genetic drift: random allele frequency change, strongest in small populations (founder effect, bottlenecks reduce diversity)

• natural selection: differential reproductive success

three types of natural selection

• directional: one extreme favored

• stabilizing: average favored

• disruptive: extremes favored, possible speciation

population genetics

• deme: interbreeding group

• gene pool: all alleles in a population

• allele frequency: proportion of allele in population

• evolution measurable through changes in allele frequencies

hardy-weinberg equilibrium

• p + q = 1

• p² + 2pq + q² = 1

• assumptions: no mutation, migration, selection, drift, or non-random mating

• if observed does not equal expected, evolution is occurring

natural selection in humans

• sickle cell and malaria

• AA = normal

• AS: heterozygote advantage (malaria resistance)

• SS: sickle cell anemia