population genetics and selection

why is genetic drift such a strong force that causes evolutionary change ?

- Gametes may not be representative of the entire parent population - Harmful alleles may increase in frequency in small populations - Favorable alleles may be lost even though they are advantageous

in the hardy weinberg principle what does it mean is a population is in equilibrium?

- allele frequencies will not change from one generation to the next -genotype frequencies will reach certain predicted frequencies and remain constant from one generation to the next

what are some ways gene flow can occur?

-animal physically moves - drifting of gametes -mating of individuals from adjacent populations

compare natural selection and evolution

-natural selection is a process, one of several proccesses tha can result in evolution -the result of evolution is that populations become better adapted to their environment ,driven by natural selection

A fruit fly population has a gene with two alleles, A1 and A2. Tests show that 70% of the gametes produced in the population contain the A1 allele. If the population is in Hardy-Weinberg equilibrium, what proportion of the flies carry both A1 and A2?

0.42

evolution is a change of gene frequency over time and hardy is saying that gene frequencies never change over time Proportions of genotypes do not change in a population if what five assumptions are met? all theses assumptions are wrong

1. No mutation takes place 2. Random mating is occurring 3. No selection occurs 4. The population size is very large 5. No genes are transferred to or from other sources (no immigration or emigration)

what are the 3 conditions for natural selection to occur and to result in evolutionary change?

1. Phenotypic variation must exist among individuals in a population 2. Variation among individuals must result in differences in the number of offspring surviving in the next generation 3. Variation must be genetically inherited

Define and contrast disruptive, stabilizing, and directional selection

1.Favors individuals at both extremes of the phenotypic range 2.Favors intermediate variants and acts against extreme phenotypes 3.Favors individuals at one extreme end of the phenotypic range

Which of the following statements explains why male peacocks with brightly colored feathers are more prevalent than those with plain colors?

Female peacocks choose the showiest males as mates, causing this trait to be more prevalent in the population.

Which of the following statements correctly describe(s) characteristics of genetic drift?

It is significant in small populations. It can cause allele frequencies to change at random. It can lead to a loss of genetic variation in a population. It can cause harmful alleles to become fixed in a population. Correct answer YOU WERE SURE AND CORRECT All of the listed responses are correct.

stabilizing selection

Natural selection that favors intermediate variants by acting against extreme phenotypes ex;In humans, infants with intermediate weight at birth have the highest survival rate

do individuals evolve?

No, populations do

if the assumptions required by hardy Weinberg equilibrium almost never hold true, why is this principle useful to researchers?

Suggest hypotheses about what process or processes are at work to cause changes to the frequencies you can look for reasons why

Define population

a group of organisms of the same species who live in the same area and interbreed, producing fertile offspring

All of the following conditions are required for Hardy-Weinberg equilibrium except __________.

a large population Unselected no gene flow Unselected random mating Unselected no mutation Correct YOU WERE UNSURE AND CORRECT natural selection

what is a bottle neck effect?

a sharp reduction in population size ex- following a natural disaster, habitat degradation

Which of the following is a possible homozygote genotype?

a. Aa b. WwQq C. BB

As improved medical technology leads to decreased infant mortality rates, how would you expect the distribution of birth weights in the human population to change?

a. More heavier babies would survive. c. More premature (underweight) babies will survive. c. The distribution of birth weights and survival would expand for higher and lower birth weights. D. There would be no change in the distribution of survival rates.

Which of the following is NOT a reason why small populations are especially vulnerable to have genetic problems?

a. They have less genetic variation, and hence less ability to adapt to changes in the environment. b. Inbreeding (mating between relatives) is more likely to happen in a small population. c. Deleterious or lethal alleles can increase in frequency by chance alone. D. Deleterious mutations happen more often in small populations.

Gene flow will cause the two populations to...

a. become genetically more different from each other. B. become genetically more similar to each other. c. not change genetically. d. become better adapted to their local environments.

A critical difference between natural selection and other mechanisms of evolution is that only natural selection...

a. causes genetic changes over time in a population. B. produces changes that are necessarily adaptive. c. produces changes in both small and large populations. d. produces random genetic changes.

Random changes in allele frequency in a population are called...

a. natural selection. b. gene flow. C. genetic drift. d. non-random mating. e. Any of the above can cause random changes in allele frequencies

Red short-horned cattle are homozygous for the red allele, white cattle are homozygous for the white allele, and roan cattle are heterozygotes. A population consists of 36% red, 16% white, and 48% roan cattle. What are the allele frequencies?

a. red = 0.36, white = 0.16 B. red = 0.6, white = 0.4 c. red = 0.5, white = 0.5 d. Allele frequencies cannot be determined unless the population is in equilibrium remember p+q=1

What is the Hardy-Weinberg principle?

allele frequencies in a population should remain constant unless one or more factors cause those frequencies to change thought evolution was mathematically impossible describes a population that is no evolving

What is an allele?

an alternative version of a gene

what type of mating increases proportion of homozygous individuals (AA or aa)?

assortative mating

A hurricane hits a small island, killing all but a few members of a bird population. This is an example of __________.

bottle neck effect

Evolution results in ____________.

change in the genetic composition of a population over time

What is a gene pool?

consists of all copies of every type of allele at every locus in all members of the population

Define disassortative mating

different individuals mate

what are the three kinds of selection?

directional, disruptive, stabilizing

what type of mating produces more heterozygotes (Aa)?

disassortative mating

A population of squirrels is preyed on by small hawks. The smaller squirrels can escape into burrows. The larger squirrels can fight off the hawks. After several generations, the squirrels in the area tend to be very small or very large. What process is responsible for this outcome?

disruptive selection

natural selection

divides population-disruptive selection shifts mean-directional selection reduces extremes-stabilizing selection

Which type of mutation plays the most important role in increasing the number of genes in the gene pool?

duplication

- What would be the result if in a population there was only one allele for a trait?

everyone would look the same

what does it mean if a researcher concludes that a population is not at hardy Weinberg equilibrium?

evolution is occurring

stabilizing selection ________

favirs intermediate variants in a population

disruptive selection

favors individuals at both extremes of the phenotypic range ex;Different beak sizes of African blackbellied seedcracker finch - Available seeds fall into 2 categories - Favors bill sizes for one or the other

directional selection

favors individuals at one extreme end of the phenotypic range ex; dark mice live on rocks , light mice live in sand

A storm separates a small number of birds in a migrating population. These birds end up at a destination different from where they usually migrate and establish a new population in this new area. This is an example of __________.

founder effect

What is genetic drift?

genetic changes in a population due to chance

Define genotype

genetic makeup of an organism, constitutes a trait

what is the raw material for selection?

genetic variation

define heterozygote

having different alleles for the same gene (Aa)

what is homozygote?

having identical alleles for the same gene (AA or aa)

natural selection changes allele frequencies become some ______survive and reproduce better that others

individuals

What is non-random mating?

individuals with certain genotypes sometimes mate with another more commonly than expected by random

what is natural selection?

individuals with traits that are best adapted to their environment have higher number of offspring in next generation

non random mating

mating with similar looking individuals-assortative mating mating with different looking individulas- disassortative mating

what is gene flow?

movement of alleles from one population to another

what are the mechanisms for evolutionary change?

mutation gene flow sexual selection genetic drift natural selection

what may genetic drift in?

non-adaptive evolotion

what happens if there is no gene flow between two isolated populations?

over time they may become different from eachother

What is the Hardy-Weinberg equation?

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

Define phenotype

physical appearance that results from expression of the genotype

what is the smallest biological unit that can evolve?

population

Magnitude of genetic drift is negatively related to

population size

Define assortative mating

similar individuals mate

genetic drift

starter population-founder effect drop in population-bottleneck individuals move into a population-gene floe

what is population genetics?

study of properties of genes in a population

In the Hardy-Weinberg equation, 2pq represents __________.

the expected frequency of the heterozygous genotype

In a large population of randomly breeding organisms, the frequency of a recessive allele is initially 0.3. There is no migration and no selection. Humans enter this ecosystem and selectively hunt individuals showing the dominant trait. When the gene frequency is reexamined at the end of the year, __________.

the frequency of the homozygous dominants will go down, the frequency of the heterozygous genotype will go down, and the frequency of the homozygous recessives will go up

What is microevolution?

the observable change in the allele frequencies of a population over time

the main source of genetic varitation among humans is?

the reshuffeling of alleles in sexual reproduction

what is the consequence of natural selection?

their traits become more common over time

If there is gene flow between two populations, what would happen with their allele frequencies over time?

they would become more similar to one another

genetic variation is the raw material for selection, what does this mean?

without any variation, there would be no evolution because all members of the species would be the same and there would be no members of a species that are better suited for survival

does genetic drift happen in every population?

yes, but its especially important in small ones

what are the agents of evolutionary change?

• Mutation • Non-random mating • Gene flow • Genetic drift • Natural selection