Unit 7 - Microevolution & Hardy Weinberg Theorem

microevolution

measure of how allele frequencies change over time, ex: beetle color is green or brown

allele

different forms of a gene

what makes evolution possible

genetic variation

genetic variation

differences in genes among individuals

sources of genetic variation

mutations and sexual reproduction

mutations

changes in DNA sequence, occur more frequently in asexually reproducing organisms, rapid reproduction gets sloppy

sexual reproduction

crossing over, independent assortment is when only half of genes are passed on and is random, random feralization

what can the hardy-weinburg equation be used to test?

whether a population is evolving

population

localized group of individuals belonging to the same species

species

group of populations whose individuals have potential to interbreed

gene pool

total aggregate of genes in a population at any one time, all alleles at all loci in all individuals

hardy weinburg theorem

frequency of alleles and genotype in a population’s gene pool remain constant over generations unless acted upon by agents other than sexual recombination or chance

hardy weinburg equilibrium

allele frequency is constant from generation to generation

required conditions for hardy weinburg equilibrium

1. very large population

2. random mating

3. isolation from other populations

4. no natural selection acting on population

5. no net mutations aka changes to DNA code

hardy weinburg equation

p+q=1 and p² + 2pq + q² = 1

p=

frequency of dominant allele

q=

frequency of recessive allele

p²=

frequency of homozygous dominant genotype (AA)

2pq=

frequency of heterozygous genotype (Aa)

q²=

frequency of homozygous recessive genotype (aa)

what can alter allele frequencies in a population?

natural selection, genetic drift, gene flow

natural selection and gene frequencies

if an allele gives the organism an advantage it will more likely be passed on and it’s frequency will increase over time

genetic drift and gene frequencies

chance events can cause allele frequencies to fluctuate especially in small populations

types of genetic drift/gene frequencies

founder effect and bottleneck effect

the founder effect and gene frequencies

few individuals isolated from a population start a new population with a different allele frequency than the original population

the bottleneck effect and gene frequencies

sudden change in the environment reduces the size of the population, by chance alone certain alleles may be over or underrepresented or absent in survivors

gene flow

transfer of alleles into or out of a population due to immigration and emigration

what is the only mechanism that constantly causes adaptive evolution

natural selection

relative fitness

the contribution an individual makes to the gene pool of the next generation relative to the contributions of other individuals

what does a genotype’s fitness depend on?

the environment in which the organism lives

what does fitness lump everything together to?

natural selection (survival, mate finding, reproduction) into 1 idea, the fittest individual is not necessarily the strongest, fastest, or biggest, a genotype’s fitness includes its ability to survive, find a mate, produce offspring, leave its genes in the next generation

types of selecetion

stabilizing, disruptive (diversifying), and directional

stabilizing selection

favors intermediates

disruptive (diversifying) selection

favors both extremes

directional selection

favors one extreme

sexual selection

individuals with certain inherited traits are more likely to obtain mates than others

why is natural selection not perfect?

only acts upon existing variations, limited by historical constraints (acts on existing structures and adaptations), adaptations are often compromises, & chance, natural selection, and environment interact