Module 5 Molgen 4500

In 1859 in On the Origin of Species, Charles Darwin wrote: "...I do not doubt that a breed of cattle, always yielding oxen with extraordinarily long horns, could be slowly formed by carefully watching which individual bulls and cows, when matched, produced oxen with the longest horns; and yet no one ox could ever have propagated its kind." What kind of selection is Darwin talking about? In plant or animal breeding, why is this type of selection commonly used?

Family selection. although offspring are sterile, parents that produce offspring with the desirable traits can be identified and chosen to produce more. this allows uncontrolled environmental variation to be cancelled out.

mutation

generation of new alleles

mutation

generation of new alleles changes allele frequencies very slowly

How does genetic drift alter the genetic variation in a population? Why is it a relatively insignificant agent of evolution in all but the very smallest populations?

genetic drift occurs when the degree of fluctuation in allele frequencies increases as the size of the population decreases. the outcome of crosses can't always be predicted. the larger the population, the more likely that deviations in one direction from our expectations are offset by deviations in the other direction. the net effect is the allele frequencies don't change.

Narrow-sense heritability for IQ scores has been estimated as 0.4. If the mean IQ score in the population is 100, what is the predicted IQ for a child whose parents both had scores of 150?

h^2 x S Selected response (S) = 150-100 = 50 (50 iq units) 0.4x50=20 Predicted IQ = 100+20 = 120

total phenotypic variance can be decomposed into all but one of these components : genetic environment interaction variance environmental variance heritability

heritability

How will variation for a gene in a given population be increased?

if migration from other populations brings into the recipient population gene alleles that are not already in the population or are present at a lower frequency.

In a human population, the genotype frequencies at one locus are 0.5 AA, 0.4 Aa, and 0.1 aa. The frequency of the A allele is:

0.70

In a tropical human population in Hardy-Weinberg equilibrium for an autosomal locus determining presence/absence of pigment in the skin, the frequency of albinism (aa) is 1 in 10,000. The frequency of heterozygotes is approximately:

1 / 50

The heterozygote frequency term for a gene with two alternate alleles A (frequency of p) and a (frequency of q) in the HW equation is:

2pq

Flower diameter in sunflowers is a quantitative trait. A plant with 6-cm flowers, from a highly inbred strain, is crossed to a plant with 30-cm flowers, also from a highly inbred strain. The F1 have 18-cm flowers. F1 × F1 crosses yield F2 plants with flowers ranging from 6 to 30 cm in diameter, in approximately 4-cm intervals (6, 10, 14, 18, 22, 26, 30). The number of different genes influencing flower diameter in this plant is. 3 4 5 6 7

3

if 64% of the people in a population are blue-eyed and the population is in HW equilibrium, what is the percentage of heterozygotes in the population?

32%

Human albinism is an autosomal recessive trait. Suppose that you find a village in the Andes where 1/4 of the population is albino. If the population size is 1000 and the population is in Hardy-Weinberg equilibrium with respect to this trait, how many individuals are expected to be heterozygotes?

500 .25 = q^2

Studying a single gene locus with 2 alleles in population (H-W equilibrium), there are 6x more heterozygotes than homozygote recessive individuals. What is the frequency of the recessive allele?

6(2pq) = q^2

The height of a type of bean plants is determined by five unlinked genes called A, B, C, D, and E. Each gene has two alleles: additive (uppercase letter) and nonadditive (lowercase letter). The shortest plants are 130 cm. The tallest plants are 220 cm. Estimate how many centimeters each allele contributes to the height difference of 90 cm.

90/5 then since 2 alleles need to /2= 9cm

Human racial differences are produced by: a. cultural factors as well as multiple genes that affect several traits b. multiple genes affect several traits c. multiple genes that affect skin color d. a single gene that affects skin color.

A

Polymorphism

A gene or trait is said to be polymorphic if there is more than one form of the trait in a population

Define "fitness". what are some critical points to keep in mind when measuring fitness?

An organisms genetic contribution to future generations. keep in mind: relativity to other genotypes/phenotypes, specific environment, reproductive success

Which chicken trait would repsond best to selection? Explain. Trait/h2 Body weight / .5 Egg production / .2

Body weight since selective parents who have better characteristics in this body weight . heritability h2 value of body weight is highest and will respond better to selection.

You and a close friend from the University of Tennessee go hiking in the mountains. You are surprised to see a salamander that is bright orange in color. Thinking that some overzealous Tennessee fans have painted this particular amphibian, you walk on. As you continue your hike, you find other salamanders of this species and note that there is variation in the coloration: some individuals are bright orange, but others are drab in color. You also note that these salamanders often eat bright orange insects. How might you explain the presence of the color polymorphism in this salamander species?

Color is inherited polygenetically with multiple alleles affecting inheritance. Insects indicate that a good deal of phenotypic variation is a result of environmental factors.

What is evolution? Describe four different mechanisms by which it can occur.

Evolution: change in allele frequencies in a population. 1) Genetic drift - random change in frequencies because of a small population size or small founder population colonizing a new habitat. 2) Migration/gene flow - new individuals added to a population, and their genetic makeup for a gene is different from that of the population. overall allele frequency in the new population changes. 3) Mutation - direct change in allele as a result of some environmal insult or problem in replication 4) Natural selection -variation for a trait, heritability for a that trait, and differential reproductive success.

Explain how inbreeding can have a positive effect on population fitness.

Gets a homozygous population, select for desirable traits, and often leads to hyrbid vigor of the generation compared to parental generation. - more robust because of dominance to mask other deleterious genes, and overdominance so the heterozygote is superior to either homozygote.

Describe two mating patterns that have an impact on genetic composition of a population.

Inbreeding - preferential mating with close relatives Assortative mating: preferential mating with individuals of dissimilar or similar genotype or phenotype.

What does it mean for a population to be in HW equilibrium?

Large population, no migration, no natural selection, random mating, no mutation.

Explain how it is that genetic variation is maintained in the population. Why is that dominant alleles do not eventually take over?

Meiotic segregation in randomly mating populations results in equilibrium distribution of genotypes after one generation. so genetic variation is maintained.

Huntington disease is caused by a single dominant gene and results in progressive mental and neurological damage. The disease is usually symptomatic when a person is between 30 and 50 years old and the patient usually dies within 15 years of diagnosis. Approximately 1 in 25,000 Caucasians have this disease. Huntington disease has not been associated with any other disease, now or in the past. Why might natural selection not have eliminated such a deleterious gene from the population?

Reach an age where symptoms show but have already produced so the gene is already passed to the next generation. Gene does not have an effect on fitness or reproduction potential.

Why is genetic drift important only in small populations?

Sampling error causes inaccurate reflection of gene frequency from generation to generation.

covariance

correlation coefficient

Two highly inbred tobacco plants are crossed. One has dark green leaves. The other has yellow leaves. The F1 have light green leaves. Five hundred progeny from F1 × F1 crosses are analyzed. Their leaves show continuous variation in color, but none has dark green or yellow leaves. What do these data suggest about the number of genes determining this trait?  a. there are 2 genes that determine this trait b. 3 genes c. 4 genes d. more than 4 genes

There are more than 4 genes that determine the trait

According to HW, if we know the frequency of each allele in the population, what can we predict?

We can predict genotypes and phenotypes we should see in the population.

Explain how and why the h^2 would change over generations of selective breeding for high egg-production.

When a characteristic has been selected for many generations, the response eventually levels off. genetic variation may be exhausted and all individuals are homozygous. No additive genetic variation, so heritability equals zero and no further response to selection can occur.

variance

a measure of dispersion of a continuous distribution

additive effects

cumulative contribution made by all the genes that contribute to a quantitative trait

The genetic frequencies of two separate populations are: Population: AA Aa aa 1: 0.36 0.48 0.16 2: 0.55 0.10 0.35 a) What are the genotypic frequencies of the two populations? b) What are the allele frequencies? c) Are the populations in Hardy-Weinberg equilibrium?

a) Expected for population 1: f(AA) = 0.36; f(Aa) = 0.48; f(aa) = 0.16 Expected for population 2: same b) Pop 1: f(A) = 0.6 = p f(a) = 1−p =0.4 = q Pop 2 : f (A) = 0.6 f(a) = 0.4 c) Population 1 is in Hardy-Weinberg equilibrium but population 2 is not.

the continuous distribution of quantitative traits is attributed to the fact that traits are influenced both by ___ and by ___ factors. a. environmental b. dominance c. measurement error d. many loci e. human error

a. environmental d. many loci

A major difference between mendelian and quantitative traits is in: a. small differences between average phenotypes compared to differences between individuals within genotypes b. large differences between average phenotypes compared to differences between individuals within genotypes c. that statistical properties of Mendelian traits are better understood d. that statistical properties of quantitative traits are better understood e. there are no differences between them

a. small differences between average phenotypes compared to differences between individuals within genotypes

genetic variance

additive dominance, genic interaction

gene pool

all genetic information within a mendelian population

gene flow between two island populations

allele frequencies become more similar across populations

genetic drift

alleles may disappear from population simply by chance

population bottle neck AND genetic drift

alleles may disappear from the population simply by chance

In a tropical human population in Hardy-Weinberg equilibrium for an autosomal locus determining presence/absence of pigment in the skin, the frequency of albinism (aa) is 1 in 10,000. The frequency of heterozygotes is approximately: a. genetic markers b. offspring c. genetic map d. controlled cross e. estimate of homozygosity in the population

an estimate of homozygosity in the population

QTL mapping requires all of the following except : genetic markers offspring a genetic map controlled cross an estimate of homozygosity in the population

an estimate of homozygosity in the population

evolution

any change in allele frequencies within a population

A gene or trait is said to be polymorphic if: a. one form exists in the population b. more than one form exists in the pop. c. allele freq. is 50:50 for each gene or trait d. allele freq. of one trait is dominant over all others

b

Which of the following is the fastest way for an enzyme to respond to changing conditions in the cell? a. changing the enzyme compartmentalization or location in the cell b. altering the enzymes activity by allosteric effectors (activators or inhibitors) c. covalently modifying the enzyme in the cell (by phosphorylation) d. controlling the synthesis or degradation of the enzyme in the cell

b

Which of the following is a concern of population genetics? a. how the cell copies its dna b. how many people have color blindness in Utah c. how proteins fold under different pH conditions d. what causes sickle cell anemia? e. why is cancer a difficult disease to treat?

b.

Population genetics is concerned with: a. how genes produce proteins b. how genes confer relative reproductive successs on individuals c. whether allele frequencies are changing over time d. how genes interact with one another

b. how genes confer relative reproductive success on the individuals c. whether allele frequencies are changing over time.

probability that two alleles are identical by descent is ____. a. coalescent b. inbreeding coefficient c. panmictic constant d. outcrossing rate e. relatedness

b. inbreeding coefficient

normal distribution

bell shaped

evolution occurs : a. only through natural selection b. only when the environment is changing c. only via natural selection, genetic drift, migration, or mutation

c by altering physical traits but not behavioral traits.

migration tends to __ genetic variation between subpopulations and __ genetic variation within each subpopulation a. increase b. not change c. reduce d. standardize e. invert

c. reduce a. increase

which of the following statistical term is not a measure of central tendency? mean mode median correlation all of the above

correlation

Flower diameter in sunflowers is a quantitative trait. A plant with 6-cm flowers, from a highly inbred strain, is crossed to a plant with 30-cm flowers, also from a highly inbred strain. The F1 have 18-cm flowers. F1 × F1 crosses yield F2 plants with flowers ranging from 6 to 30 cm in diameter, in approximately 4-cm intervals (6, 10, 14, 18, 22, 26, 30). An 18-cm F1 plant is crossed to a 6-cm plant. What is the probability of an offspring with one additive allele, if all genes that influence this trait are unlinked? a. 1/3 b. 1/4 c. 1/6 d. 3/8 e. 1/16

d.

If mating occurs solely between relatives, eventually what will happen to the population? it will become heterozygous b. remain in equilibrium c. it will become polymorphic for all shared traits d. it will become completely homozygous individuals in pop will have more dominant alleles.

d.

Inbreeding in populations that are normally outbreeding leads to which of the following? A. a smaller population B. A higher rate of mutation c. a hgiher rate of genetic drift d. more individuals affected by rare diseases e. an incrase in the freq. of heterozygotes

d.

Which of the following is NOT an explanation as to why dominant disease causing genes exist in populations? a. despite the gene's effects, individuals stay healthy enough to reproduce. b. the genes exert their effects late in life, beyond reproductive age c. the genes may be the result of new mutations d. the genes are masked and therefore, are passed only through carriers

d.

Which of the following polymorphisms is the most efficient for use in population genetics studies? a. amino acid sequence polymorphisms b. restriction site variation c. chromosomal polymorphisms d. complete sequence variation d. variable number of tandem repeats

d.

knowing the __ of a trait has great practical importance because it allows statistical predictions regarding the phenotypes of offspring to be made on the basis of the parent's __ a. variance b. inbreeding coefficient c. phenotype d. heritability e. genotype

d. heritability c. phenotype

variance

distribution around the mean

Which of the following is NOT a feature of Darwin's theory of natural selection? a. a population adapts to its environment due to the variable reproductive success of individuals b. there is no heritable variation among individuals c. individuals with poor fitness never produce offspring d. A & B e. B & C

e

In a normal distribution, 99% of the measurements fall within a. 1% of mean b 5% of mean c. plus/minus one STD. of mean d. plus/minus 2 STD of mean e. plus/minus 3 STD of mean.

e.

To establish that evolution by natural selection is operating in a population, one must demonstrate variability for a trait, heritability of that trait, differential reproductive success based on that trait, and: a. continuous change in environment b. progress c. random mating d. increased complexity of the organism e. nothing else

e.

Which statement is true regarding heritability and continuous variation? a. Heritability measures the degree to which genes determine phenotype. b. As the number of gene loci that affect a trait increases, the proportion of extreme version of the trait also increases. c. The total variance used to calculate heritability measures all the variance in a population. d. A heritability value of 0.8% of the total variance is due to differences in the environment. e. A low heritability score means that genes are less influential than environment in determining phenotypic variation.

e.

rapid changes in allele frequencies by ___ take place in populations that are _. a. mutation b. evolving c. inbred d. small e. genetic drift

e. genetic drift d. small

______________ can cause the same genotype to produce a range of potential phenotypes.

environmental effects

Any change in a population from Hardy-Weinberg equilibrium can be defined as ______.

evolution

You are studying a population of kangaroo rats. You calculate the expected frequencies of the alleles for coat color. When you compare these to the observed genotype frequencies, there is a large discrepancy. What can you deduce, based on these findings?

if the expected genotype frequencies and observed frequencies are very different, then he population is not in HW equilibrium. one of the assumptions is being violated. Random mating, large population, no mutation, no natural selection, no migration.

What effect does mutation have on genetic variation?

increases genetic variation by creating new alleles.

a mendelian population is defined by individuals: interbreeding inbreeding evolving living in close proximity migrating

interbreeding

negative directional selection

mean trait value decreases from one generation to another.

migration

movement of genes

In a population of HW equilibrium, what will the proportion of matings between homozygotes?

p4 + q4 + 2p2q2

which of the following is NOT an example of nonrandom mating? positive assortative mating, inbreeding, outreaching, panmixis, negative assortative mating

panmixis

frequency distribution

phenotype proportions

genetic correlation

pleiotrophy

inbreeding coefficient

probability of alleles being identical by descent.

slope

regression coefficient

regression

relationship between variables

Which of the following evolutionary forces does NOT change allele frequencies? nonrandom mating mutation selection drift migration

selection

Because real-life populations are, of course, not infinitely large, why is the Hardy-Weinberg condition of an "infinitely large population" usually met for natural populations?

significant deviations only occur with small populations, negligible effects occur when the population is large.

negative directional selection

the mean trait value decreases from one generation to another

The Hardy-Weinberg law (equation) is a mathematical model in which allele frequencies in populations remain constant from generation to generation. Given all the conditions that must be met for the Hardy-Weinberg equation to be valid, why is this equation useful for studying population genetics?

when assumptions are met, the law indicates that reproduction alone doesn't alter allelic or genotype frequencies and allelic frequencies determine the frequencies of genotypes. One can estimate the allelic and genotype frequencies in the population for the locus and compare them with the observed number of genotypes in the population.