Chapter 23: population genetics

What three major factors alter allele frequencies and bring about most evolutionary change?

1. Natural selection 2. genetic drift 3. gene flow 4. (mutation) (usually only applies to prokaryotes)

Why is natural selection unable to fashion perfect organisms?

1. Selection can only edit existing variations. 2. Evolution is limited by historical constraints. 3. Adaptations are often compromises. 4. Chance, natural selection and the environment interact.

What are the two processes that contribute to genetic variation and make evolution possible? Which is of greater importance for producing genetic differences?

1. mutation 2. sexual reproduction (more important)

Be able to distinguish among the three modes of selection: directional, disruptive and stabilizing.

Directional selection - selection against ONE extreme (but favoring the opposite extreme). Disruptive selection - Selection against the averages (but for the extremes). Stablaizing selection - selection for the averages (but against the extremes). ON EXAM - natural selection works on phenotypes directly, then eventually leading to genoptypes in further generations.

gene flow

Gene flow consists of genetic additions or subtractions from a population, resulting from movement of fertile individuals or gametes. Gene flow causes a population to gain or lose alleles. It tends to reduce differences between populations over time.

Be able to explain how diploidy and balancing selection help to preserve genetic variation within a population.

If natural selection takes places, how come all of the harmful alleles are not eliminated from the population? Answer: Diploidy, it maintains genetic variation in the form of hidden recessive alleles, such as carriers.

Be able to distinguish between the terms "intra" and "intersexual" selection.

Intrasexual selection - (usually male related) is competition among individuals of one sex for mates of the opposite sex....example male fighting another male for a female. Intersexual selection - (usually female related) ....example female choosing a male for looks.

What are the five conditions that must be met for the Hardy-Weinberg theorem to be valid?

Large Random M N M 1. Large Population (no genetic drift) 2. Random Mating 3. no Mutation 4. no Natural selecton 5. no Migration (no gene flow)

What is microevolution? What is the smallest unit of evolution?

Microevolution is the change in the genetic makeup (allele frequencies) of a population overtime...ONLY regarding species.

know how to calculate allele frequenciesin a population! (slide 17 and 18)

On exam even if Hardy-Weinberg equilibrium is not working, the sum of all genotype frequency must still equal 1

Genetic Variation

Phenotypic variation is not always heritable.

What is meant by the term "relative fitness"?

Relative fitness - is the ability for an organism to pass on its alleles to the next genereation. Example: to enhance reproductive success in the next generation. (more offspring)

What is the Hardy-Weinberg Theorem? What does it state?

The Hardy-Weinberg principle describes a population that is NOT evolving. It states that frequencies of alleles and genotypes in a population's gene pool REMAINS CONSTANT from generation to generation, provided that only Mendelian segregation and recombination of alleles are at work.

genetic drift

a change in allele frequencies only due to CHANCE in a SMALL POPULATON. Effects of Genetic drift: 1. Genetic drift is significant in small populations 2. Genetic drift causes allele frequencies to change at random 3. Genetic drift can lead to a loss of genetic variation within populations 4. Genetic drift can cause harmful alleles to become fixed.

"on exam half of you will mix up allele frequencies with genotype frequencies' know the difference!!!

allele freq: p + q = 1 genotype freq: p2 + 2pq + q2 = 1

What is meant by the term "frequency-dependent selection"?

as the frequency of the population becomes greater, the relative fitness decreases.

What is the bottle neck effect? founder effect?

bottle neck - a disaster like a hurricane or torando almost wipes out a population. founder effect - a group of individuals becomes isolated from a larger population. Allele frequencies in the small founder population can be different from those in the larger parent population "on exam, bottle neck, and founder effect are examples of genetic drift"

Know and be able to apply the Hardy Weinberg equation: p^2 +2pq + q^2 = 1. (slide 26 ex)

example on slide 26

neutral variation

is a genetic variation that gives no selective advantage. For example, changes in the non-coding regions of a gene are not selected for or against, so gives no advantage one way or the other.

population

is a localized group of individuals capable of interbreeding and producing fertile offsprings.

Gene pool

is the total aggregate of genes in a population at any one time.

What is meant by the term "heterozygote advantage"?

it is an example of balancing selection in which, some heterozygous individuals have a greater fitness than homozygotes. Ex. sickle cell enmia, if you are homozygous for it you will die, but if you are heterozygous for it you will be able to survive malaria better than normal people.