Deck 26: Population Genetics

Question 1

You will need to be familiar with the techniques described in Chapter 20 to answer this question. Gene polymorphisms can be detected using a variety of cellular and molecular techniques. Which techniques would you use to detect gene polymorphisms at the following levels
a. DNA level
B. RNA level
C. Polypeptide level

Answer 1

Gene polymorphism is the existence of gene in two or more allelic forms. The genetic material is the part of DNA (Deoxyribonucleic acid) in eukaryotes and part of RNA (Ribonucleic acid) in prokaryotes.
RNA is single stranded and DNA is double stranded. We cannot observe frequent polymorphisms in RNA.
Poly peptide bonds can be observed in DNA and proteins. To detect the gene polymorphisms DNA level is quite useful than RNA and polypeptide level, because RNA and polypeptides cannot give complete information of gene polymorphisms.
By analyzing DNA by using DNA finger printing or other techniques we can detect genetic polymorphism in a population.

Question 2

In a population, the frequencies of two alleles are B = 0.67 and b = 0.33. The genotype frequencies are BB = 0.50, Bb = 0.37, and bb = 0.13. Do these numbers suggest inbreeding Explain why or why not.

Answer 2

Inbreeding is the mating of genetically related species, the allelic frequency of B= 0.67, b= 0.33. Consider the alleles B=p, b=q of a population, when there is inbreeding the Genotype frequency can be calculated using the formula,
For homozygous normal individuals the genotypic frequency of BB is equals to

a..For heterozygous normal individuals the genotypic frequency of Bb is equals to

a..For homozygous recessive individuals the genotypic frequency of bb is equals to

a..Where

a.is the measure of genotype frequency deviation from the Hardy-Weinberg equation, its value ranges from -1 to +1. For inbreeding the

a.value is greater than zero, so in this way genotype frequency affected due to inbreeding.Consider the

a.value as 0.25, and then the genotypic frequency BB value can be calculated,

a.The genotypic frequency Bb value can be calculated,

a.The genotypic frequency bb value can be calculated,

a.These numbers suggest the inbreeding; because the calculated genotypic frequency coincides with the given values.

Question 3

In the term genetic drift, what is drifting Why is this an appropriate term to describe this phenomenon

Answer 3

The term random genetic drift is used in evolution of genetics. Drifting means fluctuation or change, because of this phenomenon the genetic information of the individuals changes randomly.
In this process the alleles present in gametes unite form zygote varies from generation to generation. Due to random selection error the new alleles may be generated or the existing alleles can be eliminated. Genes contains alleles, because of random genetic drift allelic frequency change is more, as the allelic frequency is changing, and the genetic change is also more. Hence, the term genetic drift is the appropriate term for the process random genetic drift.

Question 4

The allele frequency of C is 0.4 and c is 0.6. If the population is in Hardy-Weinberg equilibrium, what is the frequency of heterozygotes

A) 0.16
B) 0.24
C) 0.26
D) 0.48

Question 5

Discuss examples of positive and negative assortative mating in natural populations, human populations, and agriculturally important species.

Question 6

In the Grants' study of the medium ground finch, do you think the pattern of natural selection was directional, stabilizing, disruptive, or balancing Explain your answer. If the environment remained dry indefinitely (for many years), what do you think would be the long-term outcome

Question 7

Why is genetic drift more significant in small populations Why does it take longer for genetic drift to cause allele fixation in large populations than in small ones

Question 8

Which of the following is a factor that does not promote widespread changes in allele or genotype frequencies

A) New mutation
B) Natural selection
C) Genetic drift
D) Migration
E) Nonrandom mating

Question 9

In genetics, what does the term population mean Pick any species you like and describe how its population might change over the course of many generations.

Question 10

The ability to roll your tongue is inherited as a recessive trait. The frequency of the rolling allele is approximately 0.6, and the dominant (nonrolling) allele is 0.4. What is the frequency of individuals who can roll their tongues

Question 11

A group of four birds flies to a new location and initiates the formation of a new colony. Three of the birds are homozygous AA , and one bird is heterozygous Aa
a. What is the probability that the a allele will become fixed in the population via genetic drift
B. If fixation of the a allele occurs, how long will it take
C. How will the growth of the population, from generation to generation, affect the answers to parts A and B Explain.

Question 12

Darwinian fitness is a measure of

A) survival
B) reproductive success
C) heterozygosity of the gene pool
D) polymorphisms in a population.

Question 13

You will need to understand solved problem S4 to answer this question. The gene for coat color in rabbits can exist in four alleles termed C (full coat color), c ch (chinchilla), c h (Himalayan), and c (albino). In a population of rabbits in Hardy-Weinberg equilibrium, the allele frequencies are
C = 0.34
c ch = 0.17
c h = 0.44
c = 0.05
Assume that C is dominant to the other three alleles. c ch is dominant to c h and c , and c h is dominant to c
a. What is the frequency of albino rabbits
B. Among 1000 rabbits, how many would you expect to have a Himalayan coat color
C. Among 1000 rabbits, how many would be heterozygotes with a chinchilla coat color

Question 14

A recessive lethal allele has achieved a frequency of 0.22 due to genetic drift in a very small population. Based on natural selection, how would you expect the allele frequencies to change in the next three generations Note: Your calculation can assume that genetic drift is not altering allele frequencies in either direction.

Question 15

Describe what happens to allele frequencies as a result of the bottleneck effect. Discuss the relevance of this effect with regard to species that are approaching extinction.

Question 16

Within a particular population, darkly colored rats are more likely to survive than more lightly colored individuals. This scenario is likely to result in

A) directional selection
B) stabilizing selection
C) disruptive selection
D) balancing selection.

Question 17

Discuss the role of mutation in the origin of genetic polymorphisms. Suppose that a genetic polymorphism involves two alleles at frequencies of 0.45 and 0.55. Describe three different scenarios to explain these observed allele frequencies. You can propose that the alleles are neutral, beneficial, or deleterious.

Question 18

What evolutionary factors can cause allele frequencies to change and possibly lead to a genetic polymorphism Discuss the relative importance of each type of process.

Question 19

With regard to genetic drift, are the following statements true or false If a statement is false, explain why
a. Over the long run, genetic drift leads to allele fixation or loss
b. When a new mutation occurs within a population, genetic drift is more likely to cause the loss of the new allele rather than the fixation of the new allele
c. Genetic drift promotes genetic diversity in large populations
d. Genetic drift is more significant in small populations.

Question 20

A population occupies a diverse environment in which the fitness of some genotypes is higher in one environment while the fitness of other individuals is higher in another environment. This scenario is likely to result in

A) directional selection
B) stabilizing selection
C) disruptive selection
D) balancing selection.

Question 21

What is a genetic polymorphism What is the source of genetic variation

Question 22

Among a large population of 2 million gray mosquitoes, one mosquito is heterozygous for a body color gene; this mosquito has one gray allele and one blue allele. There is no selective advantage or disadvantage between gray and blue body color. All of the other mosquitoes carry the gray allele
a. What is the probability of fixation of the blue allele
B. If fixation happens to occur, how many generations is it likely to take
C. Qualitatively, how would the answers to parts A and B be affected if the blue allele conferred a slight survival advantage

Question 23

When two populations frequently intermix due to migration, what are the long-term consequences with regard to allele frequencies and genetic variation

Question 24

A gene exists in two alleles, and the heterozygote has the highest fitness. This scenario is likely to result in

A) directional selection
B) stabilizing selection
C) disruptive selection
D) balancing selection.

Question 25

In a large herd of 5468 sheep, 76 animals have yellow fat, compared with the rest of the members of the herd, which have white fat. Yellow fat is inherited as a recessive trait. This herd is assumed to be in Hardy-Weinberg equilibrium
a. What are the frequencies of the white and yellow fat alleles in this population
B. Approximately how many sheep with white fat are heterozygous carriers of the yellow allele

Question 26

What is the difference between a random and an adaptive evolutionary process Describe two or more examples of each. At the molecular level, explain how mutations can be random or adaptive.

Question 27

Two populations of antelope are separated by a mountain range. The antelope are known to occasionally migrate from one population to the other. Migration can occur in either direction. Explain how migration affects the following phenomena:
a. Genetic diversity in the two populations
B. Allele frequencies in the two populations
C. Genetic drift in the two populations

Question 28

Genetic drift is

A) a change in allele frequencies due to random fluctuations
B) likely to result in allele loss or fixation over the long run
C) more pronounced in smaller populations
D) all of the above.

Question 29

Most new mutations are detrimental, yet rare beneficial mutations can be adaptive. With regard to the fate of new mutations, discuss whether you think it is more important for natural selection to select against detrimental alleles or to select in favor of beneficial ones. Which do you think is more significant in human populations

Question 30

In a donor population, the allele frequencies for the common ( Hb A ) and sickle cell ( Hb S ) alleles are 0.9 and 0.1, respectively. A group of 550 individuals migrates to a new population containing 10,000 individuals; in the recipient population, the allele frequencies are Hb A = 0.99 and Hb S = 0.01
a. Calculate the allele frequencies in the conglomerate population
b. Assuming the donor and recipient populations are each in Hardy-Weinberg equilibrium, calculate the genotype frequencies in the conglomerate population prior to further mating between the donor and recipient populations
c. What will be the genotype frequencies of the conglomerate population in the next generation, assuming it achieves Hardy-Weinberg equilibrium in one generation

Question 31

Does inbreeding affect allele frequencies Why or why not How does it affect genotype frequencies With regard to rare recessive diseases, what are the consequences of inbreeding in human populations

Question 32

Which of the following types of genetic drift involve the migration of a population from one location to another

A) The bottleneck effect
B) The founder effect
C) Both a and b
D) None of the above

Question 33

State for each of the following whether it is an example of an allele, genotype, and/or phenotype frequency:
a. Approximately 1 in 2500 people of Northern European descent is born with cystic fibrosis
b. The percentage of carriers of the sickle cell allele in West Africa is approximately 13%
c. The number of new mutations for achondroplasia, a genetic disorder, is approximately 5 × 10 5.

Question 34

What is Darwinian fitness What types of characteristics can promote high fitness values Give several examples.

Question 35

Using the pedigree shown here, answer the following questions for individual VI-1:

a. Is this individual inbred
B. If so, who are her common ancestor(s)
C. Calculate the inbreeding coefficient for VI-1
d. Are the parents of VI-1 inbred

Question 36

Gene flow depends on

A) migration
B) the ability of migrant alleles to be passed to subsequent generations
C) genetic drift
D) both a and b.

Question 37

The human MN blood group is determined by two codominant alleles, M and N. The following data were obtained from various human populations:

a.
Data from E
b. Speiss (1990). Genes in Populations, 2d ed. Wiley-Liss, New York
a. Calculate the allele frequencies in these five populations
b. Which populations appear to be in Hardy-Weinberg equilibrium
C. Which populations do you think have had significant intermixing due to migration

Question 38

Here are traditional DNA fingerprints of five people: a child, mother, and three potential fathers:

a.
Which males can be ruled out as being the father Explain your answer. If one of the males could be the father, explain the general strategy for calculating the likelihood that he could match the offspring's DNA fingerprint by chance alone. (See solved problem S6 before answering this question.)
Problem S6
An important application of DNA fingerprinting is relationship testing. Persons who are related genetically have some bands or peaks in common. The number they share depends on the closeness of their genetic relationship. For example, an offspring is expected to receive half of his or her minisatellites from one parent and the rest from the other. The diagram shown here schematically illustrates a traditional DNA fingerprint of an offspring, mother, and two potential fathers.
a.
In paternity testing, the offspring's DNA fingerprint is first compared with that of the mother. The bands that the offspring have in common with the mother are depicted in purple. The bands that are not similar between the offspring and the mother must have been inherited from the father. These bands are depicted in red. Which male could be the father

Question 39

A family pedigree is shown here.
a. What is the inbreeding coefficient for individual IV-3
B. Based on the data shown in this pedigree, is individual IV-4 inbred

Question 40

Inbreeding refers to mating between individuals that are

A) homozygous
B) heterozygous
C) part of the same genetic lineage
D) both a and c.

Question 41

The term polymorphism can refer to both genes and traits. Explain the meaning of a polymorphic gene and a polymorphic trait. If a gene is polymorphic, does the trait that the gene affects also have to be polymorphic Explain why or why not.

Question 42

What is the intuitive meaning of the mean fitness of a population How does its value change in response to natural selection

Question 43

A family pedigree is shown here.
a. What is the inbreeding coefficient for individual IV-2 Who is/ are her common ancestors
B. Based on the data shown in this pedigree, is individual III-4 inbred

Question 44

The mutation rate is

A) the likelihood that a new mutation will occur in a given gene
B) too low to substantially change allele frequencies in a population
C) lower for mutations that create beneficial alleles
D) all of the above.

Question 45

You will need to understand solved problem S4 before answering this question. In an island population, the following data were obtained for the numbers of people with each of the four blood types:

a.
Is this population in Hardy-Weinberg equilibrium Explain your answer.

Question 46

What is DNA fingerprinting How can it be used in human identification

Question 47

Antibiotics are commonly used to combat bacterial and fungal infections. During the past several decades, however, antibiotic-resistant strains of microorganisms have become alarmingly prevalent. This has undermined the effectiveness of antibiotics in treating many types of infectious disease. Discuss how the following processes that alter allele frequencies may have contributed to the emergence of antibiotic-resistant strains:
a. Random mutation
B. Genetic drift
C. Natural selection

Question 48

The transfer of an antibiotic resistance gene from one bacterial species to a different species is an example of

A) exon shuffling
B) horizontal gene transfer
C) genetic drift
D) migration.

Question 49

Cystic fibrosis (CF) is a recessive autosomal trait. In certain populations of Northern European descent, the number of people born with this disorder is about 1 in 2500. Assuming Hardy-Weinberg equilibrium for this trait:
a. What are the frequencies for the normal and CF alleles
B. What are the genotype frequencies of homozygous normal, heterozygous, and homozygous affected individuals
C. Assuming random mating, what is the probability that two phenotypically unaffected heterozygous carriers will choose each other as mates

Question 50

Describe the similarities and differences among directional, balancing, disruptive, and stabilizing selection.

Question 51

Let's suppose the mutation rate for converting a B allele into a b allele is 10 4. The current allele frequencies are B = 0.6 and b = 0.4. How long will it take for the allele frequencies to equal each other, assuming that no genetic drift is taking place

Question 52

DNA fingerprinting analyzes the DNA from individuals based on the occurrence of ___________________ in their genomes

A) repetitive sequences
B) abnormalities in chromosome structure
C) specific genes
D) viral insertions

Question 53

Resistance to the poison warfarin is a genetically determined trait in rats. Homozygotes carrying the resistance allele ( WW ) have a lower fitness because they suffer from vitamin K deficiency, but heterozygotes ( Ww ) do not. However, the heterozygotes are still resistant to warfarin. In an area where warfarin is applied, the heterozygote has a survival advantage. Due to warfarin resistance, the heterozygote is also more fit than the normal homozygote (ww). If the relative fitness values for Ww, WW, and ww individuals are 1.0, 0.37, and 0.19, respectively, in areas where warfarin is applied, calculate the allele frequencies at equilibrium. How would this equilibrium be affected if the rats were no longer exposed to warfarin

Question 54

When analyzing the automated DNA fingerprints of a father and his biological daughter, a technician examined 50 peaks and found that 30 of them were a perfect match. In other words, 30 out of 50 peaks, or 60%, were a perfect match. Is this percentage too high, or would you expect a value of only 50% Explain why or why not.

Question 55

A gene pool is

A) all of the genes in a single individual
B) all of the genes in the gametes from a single individual
C) all of the genes in a population of individuals
D) the random mixing of genes during sexual reproduction.

Question 56

For a gene existing in two alleles, what are the allele frequencies when the heterozygote frequency is at its maximum value, assuming a Hardy-Weinberg equilibrium What if there are three alleles

Question 57

Do the following examples describe directional, disruptive, balancing, or stabilizing selection
a. Polymorphisms in snail color and banding pattern as described in Figure 26.12
B. Thick fur among mammals exposed to cold climates
C. Birth weight in humans
D. Sturdy stems and leaves among plants exposed to windy climates
FIGURE 26.12 Polymorphism in the land snail, Cepaea nemoralis. (a) This species of snail can exist in several different colorsand banding patterns. (b) Coloration of the snails is correlated with thespecific environments where they are located.

Question 58

In natural populations, most genes are

A) polymorphic
B) monomorphic
C) recessive
D) both a and c.

Question 59

What is the gene pool How is a gene pool described in a quantitative way

Question 60

Describe, in as much experimental detail as possible, how you would test the hypothesis that snail color distribution is due to predation.

Question 61

What would you expect to be the minimum percentage of matching peaks in an automated DNA fingerprint for the following pairs of individuals
a. Mother and son
B. Sister and brother
C. Uncle and niece
D. Grandfather and grandson

Question 62

A gene exists in two alleles designated D and d. If 48 copies of this gene are the D allele and 152 are the d allele, what is the allele frequency of D

A) 0.24
B) 0.32
C) 0.38
D) 0.76