Evolution Test #2

A type of evolution that happens within a single population. It occurs when there is a change in a population’s allele frequencies from one generation to the next. E.g. Mosquitoes evolving to grow a resistance to DDT.

Chance events change the frequency of traits in a population, NOT an adaption or selection.

It can have major effects, especially in smaller populations, because each individual’s alleles represent a large fraction of the gene pool. Therefore it’s more likely that more genes can be lost from these chance events and affect the population more.

A type of genetic drift when a new population is started by only a small group of individuals.

E.g. The O blood type is almost completely in the South American population because of a high frequency of this gene in the colonizers that first populated the continent.

A type of genetic drift that occurs when a large population is drastically reduced by a disaster like famine, natural disaster, loss of habitat, human hunting etc.

E.g. Cheetahs, who share a small number of alleles. This is due to 2 bottleneck events, the Ice Age and, more recently, overhunting and habitat loss.

The migration of fertile individuals or the transfer of gametes between populations

E.g: a bee carrying pollen from one flower population to another

Extensive gene flow can eventually group neighbouring populations into a single population

Transmitted in gametes immediately changes that gene pool of a population by substituting one allele for another. The mutation's effect on the gene pool only shows up after many generations.

This rate can be increased if the mutation is chosen through natural selection or genetic drift. In other words, the mutation has to be beneficial and acted upon by natural selection to influence microevolution. Mutations are the only source of new genetic material.

Selection passes on alleles to the next generation in disproportionate number It is the only agent of microevolution that is adaptive since it accumulates and maintains favourable genotypes Genetic variation makes this possible

When one extreme of a trait is favoured over the other. E.g: Giraffe neck lengths. The longer the necks, the more advantageous.

When the ‘extreme’ traits are selected against, and the middle versions of the trait are favoured. E.g. Human baby weight. Too light and too heavy babies are more likely to die and are therefore selected against.

When both extreme traits are favoured, and the medium traits are selected against. E.g. dark and light-coloured oysters. Both dark-coloured and light-coloured oysters have camouflage advantages, but those in-between these colours have no advantages and are therefore selected against.

Describes a non-evolving population, and allele frequencies will stay constant unless acted upon by other agents. Alleles are present in the gene pool of new populations at the same frequencies as in the original gene pool. This opposes microevolution which is when frequencies of alleles in gene pools DO change from one generation to the next.

• Large breeding population

• Random mating

• No mutations

• No immigration or emigration

• No natural selection

Helps to ensure that chance alone does not disrupt genetic equilibrium. Large populations combat the impact of genetic drift (which disrupts equilibrium) because genetic drift does not significantly affect large populations.

Mating must be random because in assortive mating, individuals tend to choose mates similar to themselves, which would result in fewer heterozygous individuals than one you would expect in a population with non-random mating.

For a population to be at equilibrium, there can be no changes in allelic frequency due to mutation because that would change the balance of alleles in the gene pool.

For the allelic frequency to remain constant in a population at equilibrium, no new alleles can be introduced and no alleles can be lost since it would alter allelic frequencies.

In a population at equilibrium, no alleles are selected over other alleles. If selection occurs, those alleles that are selected would become more common and mess with the gene frequencies

p + q = 1

p^2 + 2pq + q^2 = 1

Dominant allele

Recessive allele

Refers to larger evolutionary changes that result in new species. E.g: The Galapagos finches went through adaptive radiation and diverged into different species through evolution. They can no longer interbreed with each other.

When a population splits into two isolated groups by geographical barrier. This is a physical barrier.

When two population diverge in the same area (they split due to other factors)

Barriers that occur after zygote formation

A type of sympatric speciation in which species occur in the same region but occupy different habitats, so they rarely encounter each other and are therefore reproductively isolated.

There are two species of garter snakes that live in the same area, but one lives in the water, and the other is terrestrial.

A type of sympatric speciation in which species that breed during different times of day, seasons, or years cannot mix gametes. They are therefore reproductively isolated.

The eastern spotted and western spotted skunks overlap in range, but eastern spotted skunks mate in late winter, and western spotted skunks mate in late summer.

A type of sympatric speciation in which species display unique behavioural patterns and rituals, such as courtship rituals or mating calls, which isolate species and attract mates of the same species. They are reproductively isolated.

Blue-footed boobies mate only after a courtship display unique to their species.

A type of sympatric speciation in which morphological differences can prevent successful mating. They are reproductively isolated.

Even in closely related species of plants, the flowers often have distinct appearances that attract different pollinators such as two species of monkey flower differ greatly in shape & colour, therefore cross-pollination does not happen

A type of sympatric speciation in which sperm of one species may not be able to fertilize eggs of another species due to either a biochemical barrier (sperm cannot penetrate the egg) or a chemical incompatibility (sperm cannot survive in female reproductive tract)

Sea urchins release sperm and eggs into surrounding waters, where they fuse & form zygotes. Gametes of different species—red& purple —are unable to fuse.

Barriers that occur before zygote formation

A type of sympatric speciation in which genes of different parent species may interact & impair the hybrid’s development

Species of salamanders may interbreed, but most hybrids do not complete development & those that do are frail.

A type of sympatric speciation in which if hybrids are vigorous, they may be sterile and chromosomes of parents may differ in number or structure.

Mules are rigorous but infertile. Horses have 64 chromosomes (32 pairs) and donkeys have 62 chromosomes (31 pairs). Mules have 63 chromosomes.

A type of sympatric speciation in which hybrids may be fertile & viable in the first generation, but when they mate, offspring are feeble or sterile

In cultivated rice strains, hybrids are vigorous, but plants in the next generation are small and sterile on the path to separate species.

The gradual divergence over long spans of time. It supports the assumption that big changes occur as the accumulation of many small ones

The rate of speciation is not constant with rapid bursts of change. There are long periods of little or no change.