Chapter 6 - Evolution of Populations: Micoevolution (Exam 1)

Genetic variation characterizes

nearly all natural populations

Gene Pool

A single individual only has some alleles found in the population

All the genes, including all the different alleles for each gene, that are present in a population at any one time

Microevolution

evolution at population level

(seen via change in frequency alleles from one generation to the next)

Artificial Selection

Selection by humans for breeding of useful traits from the natural variation among different organisms

Allele Frequencies

measure the amount of genetic variation in a population

the relative abundances of alleles of a given gene among all individuals of a population

Genotype Frequencies

show how a populations genetic variation is distributed among its members

If population is Hardy-Weinberg

- population is not changing genetically

- population is not evolving

Hardy-Weinberg equilibrium

condition that occurs when the frequency of alleles in a particular gene pool remain constant over time

Hardy-Weinberg Equilibrium Assumptions

- no mutation

- no migration

- large (infinite) population

- random mating

- no natural selection

All alleles should add to 100%

p + q = 100

(p^2) + 2pq + (q^2) = 1.00

Frequency

Genotype

Phenotype

(1)p 2pq (1)q

RR Rr rr

red red white

Importance of Hardy-Weinberg?

to see if evolution is occurring or not and what is the cause

(compare expected genotypes, phenotypes, and frequencies)

Changes in allele frequencies and genotype frequencies are caused by

- mutation

- gene flow

- genetic drift

- assortative (non-random) mating

- natural selection

Mutation

-change one allele into another

- most are neutral or harmful

- few beneficial ones change environment (ultimate source of evolution)

Gene Flow

migration of individuals between/among populations

(immigrants add new alleles and change frequencies)

Genetic Drift

- chance fluctuation in gene pool

(more common in smaller populations and random with respect to fitness)

- overrides natural selection only in small populations

- mutations more likely to become fixed

bottleneck effect

large population goes through period when only a small number of individuals survive (cheetahs)

A change in allele frequency following a dramatic reduction in the size of a population

Founder effect

new population established by few individuals (new gene frequencies compared to parent population)

change in allele frequencies as a result of the migration of a small subgroup of a population

Founder Events

- colonization of isolated habitats

(islands, mountains, caves, ponds)

- Fruit Fly (old world) high variation

(new world) low variation

Assortative Mating

-individuals mating non-randomly = sexual selection

-genotypes will change from expected

- mate more often with individuals with same/different genotypes than randomly selected

sexual selection

can cause sexual dimorphism

when individuals select mates based on heritable traits

Natural Selection

-differences in reproductive success (survival of fitness)

- only evolutionary agent that adapts populations to their environment

- preserve allele frequencies or cause them to change

Natural Selection has three factors

- Stabilizing

- Directional

- Disruptive

(can change traits influenced by multi-loci)

Directional Selection

population goes towards one way (ex. all dark mice)

- cold spell survivors will be directional

Diversifying (disruption) selection

population favors extremes (extremally white or extremally black)

- birds with beaks for each seed

Stabilizing selection

favors in-between (ex. all grayish mice)

- babies medium so don't die

Does assortative or non-random mating create new species?

yes to both

Most populations are genetically highly variable

random genetic drift, stabilizing selection, and natural selection tend to reduce genetic variation

Why bother with sexual reproduction; it reduces reproductive output?

gives a variety of genotypes that can increase survivability of populations (especially variable/changing environments)

Sexual reproduction

does not influence frequencies of alleles, rather generates new combinations of genetic material

(natural selection determines combinations are most successful)

Sometimes genetic variation within species is maintained in distinct sub-populations due to

tradeoffs (cyanide production in a plant)

Genotypes do not uniquely determine

phenotypes (phenotype A can be produced by more than one genotype like AA or Aa)

Organisms phenotype results in

complex series of developmental processes influenced by both genes and environmental factors (Nature vs. Nurture)

Natural Selection modifications?

- does not modify individual

- modifies ONLY what already exists

- not predeterminate (deterministic)

- Natural Selection is blind

Constraints on evolution

- eye

- knee joints

- spinal column

What are vestigial traits?

structures left over from ancestor (tail bone)

Infrequent/slowly occurring events unlikely to be observed in microevolution studies can influence

macroevolutionary change

Additional evidence needed to understand why evolution took place in particular course is a

chance event

Psychological evidence suggests sex differences in morphology have been modified by sexual selection so

to attract mates (intersexual selection) or intimidate rivals (intrasexual selection)

Men choose women on

distribution of fat reserves and by exaggerating morphological indicators of youthfulness

Women choose men on

social dominance, and intimidating reproductive rivals

Secondary sexual characteristics also provide cues to hormonal status and phenotypic quality

low waist hip ratio, enlarged breasts, beards, etc.