Deck 25: Population Genetics

Question 1

A new kind of tulip is produced that develops only purple or pink flowers. Assume that flower color is controlled by a single-gene locus and that the purple allele (C) is dominant to the pink allele (c). A random sample of 1000 tulips from a large cultivated field yields 847 purple flowers and 153 pink flowers. Estimate the proportion of all purple flowering plants that are heterozygotes and homozygotes.

A) heterozygotes = 694, homozygotes = 153
B) heterozygotes = 565, homozygotes = 282
C) heterozygotes = 476, homozygotes = 372
D) heterozygotes = 424, homozygotes = 423
E) heterozygotes = 0, homozygotes = 847

Answer 1

C

Question 2

If there are two alleles, A and a, in a population and the population is at Hardy-Weinberg equilibrium, which frequency of A would produce the greatest frequency of heterozygotes?

A) 0.1
B) 0.25
C) 0.5
D) 0.75
E) 1

Answer 2

C

Question 3

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?

Answer 3

not answered

Question 4

You are studying cannibals in Borneo and want to determine if a specific village population is in Hardy-Weinberg equilibrium with respect to the two co-dominant M and N blood type alleles (L^M, L^N) segregating at the single-gene locus. Choose the answer below that gives the correct expected number of M, MN, and N individuals and the critical value to which you will compare your chi-square value (see Table 3.7 for critical values). $\begin{array}{lllc}&&&\underline{ Phenotypes }\\\text { M } & \text { MN } &N& \text { Total \# genotypes } \\287 & 665 & 123 & 1075\end{array}$

A) M = 357, MN = 525, N = 193; chi-square critical value = 5.991
B) M = 0.331, MN = 0.488, N = 0.180; chi-square critical value = 3.814
C) M = 357, MN = 525, N = 193; chi-square critical value = 3.814
D) M = 0.267, MN = 0.619, N = 0.114; chi-square critical value = 3.814
E) M = 287, MN = 665, N = 123; chi-square critical value = 7.815

Question 5

Use Figure 25.3 to determine the BEST answers for the following question.

-When a population is in Hardy-Weinberg equilibrium, what is the approximate frequency of the aa homozygote and the Aa heterozygote when the frequency of AA is approximately 0.5?

A) aa = 0.25, Aa = 0.25
B) aa = 0.25, Aa = 0.5
C) aa = 0.02, Aa = 0.48
D) aa = 0.1, Aa = 0.4
E) aa = 0.4, Aa = 0.1

Question 6

Human blood type is determined by three alleles I^A, I^B, and I^O. The alleles I^A and I^B are co-dominant to each other, and both are dominant to I^O. Within a large, randomly mating population (540,000 individuals), the frequencies for the blood type alleles are 0.3 for the I^A allele, 0.6 for the I^O allele, and 0.1 for the I^B allele. Calculate the expected numbers of people in the population having each of the blood types A, B, AB, and O.

A) A = 243,000 people, B = 70,200 people, AB = 32,400 people, and O = 194,400 people
B) A = 162,000 people, B = 54,000 people, AB = 3,240 people, and O = 324,000 people
C) A = 48,600 people, B = 5,400 people, AB = 32,400 people, and O = 194,400 people
D) A = 194,400 people, B = 64,800 people, AB = 32,400 people, and O = 194,400 people
E) A = 243,000 people, B = 5,400 people, AB = 32,400 people, and O = 194,400 people

Question 7

DNA typing is used to compare evidence DNA (E) left at a crime scene to two suspects (S1 and S2). Suspect 1 is excluded by the evidence, but suspect 2 remains included. What is the frequency of suspect 2's genotype if the allelic frequencies in the population are f(A₁) = 0.1, f(A₂) = 0.2, and f(A₃) = 0.7, and the population is at Hardy-Weinberg equilibrium?

A) 0.01
B) 0.02
C) 0.04
D) 0.28
E) 0.49

Question 8

One way to define _____ is any change in allelic frequencies within a population.

A) mutation
B) natural selection
C) equilibrium
D) evolution
E) sampling error

Question 9

Suppose that in a population the frequency of a particular recessive condition is 1/400. Assume the presence of only a dominant allele (A) and a recessive allele (a) in the population and that the population is at Hardy-Weinberg equilibrium. What is the frequency of heterozygotes in the population?

A) 0.0025
B) 0.05
C) 0.095
D) 0.9025
E) 0.0475

Question 10

You are studying cannibals in Borneo and collect the following data with the two co-dominant M and N blood type alleles (L^M, L^N) segregating at the single-gene locus. What are the genotypic and allelic frequencies for this population? $\begin{array}{lllc}&&&\underline{ Phenotypes }\\\text { M } & \text { MN } &N& \text { Total \# genotypes } \\287 & 665 & 123 & 1075\end{array}$

A) L^M L^M = 0.287, L^M L^N = 0.665, L^N L^N = 0.123; L^M = 0.885, L^N = 0.115
B) L^M L^M = 0.267, L^M L^N = 0.619, L^N L^N = 0.114; L^M = 0.5, L^N = 0.5
C) L^M L^M = 0.267, L^M L^N = 0.619, L^N L^N = 0.114; L^M = 0.267, L^N = 0.114
D) L^M L^M = 0.267, L^M L^N = 0.619, L^N L^N = 0.114; L^M = 0.576, L^N = 0.424
E) L^M L^M = 0.287, L^M L^N = 0.665, L^N L^N = 0.123; L^M = 0.576, L^N = 0.424

Question 11

If there is random mating in a population and no evolutionary forces are acting on the population, what will be the expected outcome?

A) The allelic frequencies will remain the same, but the genotypic distribution will change.
B) The genotypic distribution will remain the same, but the allelic frequencies will change.
C) Both the genotypic distribution and the allelic frequencies will change.
D) Both the genotypic distribution and the allelic frequencies will remain the same.
E) No prediction can be made about the genotypic distribution and allelic frequencies from one generation to the next.

Question 12

Suppose that in a population the frequency of a particular recessive condition is 1/400. Assume the presence of only a dominant allele (A) and a recessive allele (a) in the population and that the population is at Hardy-Weinberg equilibrium. What is the frequency of the recessive allele that causes the condition?

A) 0.000625
B) 0.0025
C) 0.025
D) 0.05
E) 0.95

Question 13

A Mendelian population is defined by individuals that are:

A) interbreeding.
B) inbreeding.
C) evolving.
D) segregating.
E) migrating.

Question 14

Which of the following does NOT bring about evolution in a population?

A) small population size
B) migration of individuals from a population with a different genetic structure
C) mutation
D) selection
E) random mating

Question 15

The _____ is all of the genetic information within a Mendelian population.

A) effective population size
B) Hardy-Weinberg equilibrium
C) fitness
D) genotypic frequency
E) gene pool

Question 16

Use Figure 25.3 to determine the BEST answers for the following question.

- When a population is in Hardy-Weinberg equilibrium and p = 0.1 and q = 0.9, what are the approximate genotypic frequencies?

A) AA = 0.01, Aa = 0.18, aa = 0.81
B) AA = 0.81, Aa = 0.18, aa = 0.01
C) AA = 0.25, Aa = 0.5, aa = 0.25
D) AA = 0.2, Aa = 0.6, aa = 0.2
E) AA = 0.05, Aa = 0.4, aa = 0.55

Question 17

Human blood type is determined by three alleles I^A, I^B, and I^O. The alleles I^A and I^B are co-dominant to each other, and both are dominant to I^O. Within a large, randomly mating population (540,000 individuals), the frequencies for the blood type alleles are 0.3 for the I^A allele, 0.6 for the I^O allele, and 0.1 for the I^B allele. What percentage of the type B people are heterozygotes (I^BI^O)?

A) 12%
B) 13%
C) 92.3%
D) 6%
E) 60%

Question 18

When considering the gene pool of a population, Hardy-Weinberg equilibrium may apply to:

A) only the entire genome but not individual loci.
B) one locus but not necessarily another.
C) dominant and recessive alleles but not codominant alleles.
D) only to the effective number of breeders.
E) only autosomal but not X-linked loci.

Question 19

A new kind of tulip is produced that develops only purple or pink flowers. Assume that flower color is controlled by a single-gene locus and that the purple allele (C) is dominant to the pink allele (c). A random sample of 1000 tulips from a large cultivated field yields 847 purple flowers and 153 pink flowers. What is the frequency of the purple and pink alleles in this field population?

A) purple allele frequency = 0.847, pink allele frequency = 0.153
B) purple allele frequency = 0.153, pink allele frequency = 0.847
C) purple allele frequency = 0.82, pink allele frequency = 0.18
D) purple allele frequency = 0.61, pink allele frequency = 0.39
E) purple allele frequency = 0.39, pink allele frequency = 0.61

Question 20

Use Figure 25.3 to determine the BEST answers for the following question.

-When a population is in Hardy-Weinberg equilibrium, what is the significance of two alleles with equal frequencies (p = q = 0.5)?

A) These are the allelic frequencies found in most populations.
B) These allelic frequencies maximize the proportion of homozygotes in the population.
C) These allelic frequencies maximize the proportion of heterozygotes in the population.
D) These allelic frequencies guarantee that neither allele will become fixed in a population.
E) These allelic frequencies minimize the proportion of heterozygotes in the population.

Question 21

Like the ABO blood type antigens, the co-dominant M-N antigens are also present in human red blood cells. A sample of 5631 individuals in a population was examined for M-N antigens, and the results follow.
a. Calculate the frequency of each allele in the population.
b. Are the M-N genotypes in Hardy-Weinberg equilibrium?
• Blood type M (L^ML^M): 1245 individuals
• Blood type MN (L^ML^N): 3421 individuals
• Blood type N (L^NL^N): 965 individuals

Question 22

If a population is in Hardy-Weinberg equilibrium, the allelic and genotypic frequencies will not change. Prove the preceding statement for a pair of alleles in population X, which is in Hardy-Weinberg equilibrium.

Question 23

_____ increases the frequency of homozygotes in a population compared to the results of random mating.

A) Inbreeding
B) Migration
C) Outcrossing
D) Genetic drift
E) Directional selection

Question 24

You are studying a single-gene locus with two alleles in a population that is in Hardy-Weinberg equilibrium. Examination of a large sample of individuals from the population reveals there are six times as many heterozygotes as there are homozygote recessive individuals in this population. What is the frequency of the recessive allele?

Question 25

You are studying the population in Iceland for X-linked alleles, and sampling experiments indicate that about 6% of the men have red-green color blindness (caused by a recessive, X-linked allele c). Assume that the population in Iceland mates randomly.
a. What percentage of men will carry the allele c? What percentage of women will carry at least one copy of the allele?
b. What percentage of women is expected to be color blind?
c. What percentage of the total population is color blind?
d. What percentage of color-blind individuals are men?
e. What percentage of individuals in the population is expected to be normal carriers for the color-blind allele?
f. After two generations, what percentage of men in the population is expected to be color blind? To have normal vision?

Question 26

_____ is the product of sampling errors and chance events that may result in changes in allelic frequencies.

A) Mutation
B) Genetic drift
C) Directional selection
D) Inbreeding
E) Evolution

Question 27

If the frequency of a recessive disease causing allele (q) is 0.005, what is the frequency of individuals with the disease in a population with an inbreeding coefficient of 0.25?

A) 0.00127
B) 0.000025
C) 0.991
D) 0.00125
E) 0.0025

Question 28

The Hardy-Weinberg law (equation) is a mathematical model in which allelic 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?

Question 29

When an allele has a frequency of 1.0 in a population, it is _____ in the population.

A) lost
B) dominant
C) overdominant
D) fixed
E) recessive

Question 30

Evolutionary geneticists carefully genotype a population of saber-toothed tigers and find the following genotypes: 250 tigers are A¹/A¹, 500 tigers are A¹/ A², and 250 tigers are A²/A². Tragically, an asteroid lands in the middle of the population, killing 50% of each genotype. What will the genotypic frequencies be in the next generation?

Question 31

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

Question 32

A population consists of 100 individuals of the following genotypes: a. What is the frequency of the A allele?
b. What is the frequency of the a allele?
c. Is the population at Hardy-Weinberg equilibrium? Explain your answer.
d. What agent of evolution would systematically produce this genotypic distribution?

Question 33

You are studying cannibals in Borneo and want to determine if a specific village population is in Hardy-Weinberg equilibrium with respect to the two co-dominant M and N blood type alleles (L^M, L^N) segregating at the single-gene locus. The following are sample data from this population of the cannibals: a. Calculate the genotypic frequencies.
b. Calculate frequencies for the L^M and L^N alleles.
c. Determine whether this population of Borneo cannibals is in Hardy-Weinberg equilibrium.

Question 34

The _____ measures the probability of alleles being identical by descent.

A) selection coefficient
B) inbreeding coefficient
C) gene pool
D) Hardy-Weinberg law
E) migration rate

Question 35

Which of the following evolutionary forces does NOT normally change allelic frequencies?

A) nonrandom mating
B) mutation
C) selection
D) drift
E) migration

Question 36

Genetic diseases in humans are usually rare and recessive. Why are the frequencies of alleles that cause rare, recessive diseases (or other recessive traits, for that matter) generally much higher than the frequency of the diseases (or traits) themselves?

Question 37

The only way for evolution to take place is if there is _____ within a population.

A) nonrandom mating
B) natural selection
C) genetic drift
D) Hardy-Weinberg equilibrium
E) genetic variation

Question 38

Human blood type is determined by three alleles I^A, I^B, and I^O. The alleles I^A and I^B are co-dominant to each other, and both are dominant to I^O. Within a large, randomly mating population (540,000 individuals), the frequencies for the blood type alleles are 0.3 for the I^A allele, 0.6 for the I^O allele, and 0.1 for the I^B allele.
a. Calculate the expected numbers of people in the population having each of the blood types A, B, AB, and O.
b. Determine the percentage of type B people that are heterozygotes (I^BI^O).

Question 39

A new kind of tulip is produced that develops only purple or pink flowers. Assume that flower color is controlled by a single-gene locus and that the purple allele (C) is dominant to the pink allele (c). A random sample of 1000 tulips from a large cultivated field yields 847 purple flowers and 153 pink flowers.
a. Determine the frequency of the purple and pink alleles in this field population.
b. Estimate the proportion of all purple flowering plants that are heterozygotes and homozygotes.

Question 40

You discover a certain species of weed growing in soil contaminated with toxic PCBs and later determine that the PCB resistance is due to a single dominant allele.
a. If 45% of the seeds from a randomly mating population of resistant weeds will germinate in contaminated soil, what is the frequency of the PCB-resistance allele?
b. Among all the plants that germinate, what proportion will be heterozygous?
c. What proportion will be homozygous dominant?

Question 41

Which agent of evolution is most likely responsible for the decrease in the frequency of a recessive allele as shown in the accompanying below?

A) genetic drift
B) natural selection
C) mutation
D) assortative mating
E) inbreeding

Question 42

The evolutionary force of _____ tends to increase genetic variation within a population but decrease genetic variation between populations, while the evolutionary force of _____ tends to decrease genetic variation within a population but increase genetic variation among populations.

A) migration; genetic drift
B) mutation; some types of natural selection
C) genetic drift; migration
D) some types of natural selection; mutation
E) positive assortative mating; negative assortative mating

Question 43

The A¹ allele mutates into the A² allele at a rate of 4 × 10^-5 and the A² allele mutates into the A¹ allele at a rate of 1 × 10^-5. Assuming no other evolutionary forces are at work, the frequency of the A² allele will eventually be:

A) 0.8.
B) 0.2.
C) 0.5.
D) 0.25.
E) 1.0.

Question 44

_____ refers to the situation where the heterozygote has a lower fitness than both homozygotes (W₁₁ > W₁₂ < W₂₂).

A) Overdominance
B) Hardy-Weinberg equilibrium
C) Underdominance
D) Heterozygote superiority
E) Genetic rescue

Question 45

If the relative fitness of the A¹A¹ genotype is 0.6, A¹A² is 1.0, and A²A² is 0.9, eventually the frequency of the A² allele will be:

A) 0.8.
B) 0.2.
C) 0.0.
D) 0.4.
E) 0.6.

Question 46

Mutation has what effect on a population?

A) It creates or increases genetic variation.
B) It promotes the fixation of alleles.
C) It reduces the amount of genetic variation.
D) It homogenizes genetic variation across populations.
E) It increases rates of outcrossing.

Question 47

_____ has the effect of homogenizing allelic frequencies among populations.

A) Migration
B) Sampling error
C) Directional selection
D) Assortative mating
E) Selection-mutation equilibrium

Question 48

_____ is the movement of genes between populations.

A) Evolution
B) Migration
C) Positive assortative mating
D) Outcrossing
E) Genetic drift

Question 49

The frequency of q in population 1 is 0.8 and the frequency of q in population 2 is 0.3. If the migration rate from population into population 2 is 0.2, what will be the frequency of q in population in the next generation?

A) 0.4
B) 0.6
C) 0.5
D) 0.1
E) 0.0

Question 50

Rapid changes in allelic frequencies by _____ take place in populations that are small.

A) mutation
B) natural selection
C) inbreeding
D) outbreeding
E) genetic drift

Question 51

_____ ultimately produces all new genetic variation in a population.

A) Outcrossing
B) Migration
C) Evolution
D) Mutation
E) Equilibrium

Question 52

In overdominance, the HIGHEST fitness is found in which genotype?

A) homozygote for the dominant allele
B) homozygote for the recessive allele
C) heterozygote
D) mutant
E) inbred recessive

Question 53

_____ is when the heterozygote has a higher fitness than either of the two homozygotes (W₁₁ < W₁₂ > W₂₂). Allelic frequencies will change in this population until _____.

A) Underdominance; an allele is fixed
B) Homeostasis; Hardy-Weinberg equilibrium is achieved
C) Dominance; a tipping point is passed
D) Recombination; linkage equilibrium is obtained
E) Overdominance; a stable equilibrium is reached

Question 54

Through _____, alleles may disappear from a population simply by chance.

A) negative directional selection
B) genetic rescue
C) genetic drift
D) fixation
E) underdominance

Question 55

Suppose a disease is caused by a recessive allele. Individuals with the disease produce only about 60% of the offspring of individuals with the normal phenotype. The mutation rate from the dominant to the recessive allele is 1 × 10^-5. At mutation-selection equilibrium, what will be the frequency of the recessive allele?

A) 0.005
B) 0.000025
C) 0.004
D) 0.00002
E) 0.0

Question 56

Which agent of evolution tends to reduce genetic variation between populations and increase genetic variation within each population?

A) natural selection
B) mutation
C) migration
D) inbreeding
E) genetic drift

Question 57

Genetic diseases in humans are usually rare and recessive. Why are the frequencies of alleles that cause rare, recessive diseases (or other recessive traits, for that matter) generally much higher than the frequency of the diseases (or traits) themselves?

A) Diseases caused by dominant alleles are generally lethal, and so most diseases are caused by recessive alleles.
B) Most of the rare, recessive alleles within the population are "hidden" within heterozygote carriers, which do not manifest the disease (or express the trait).
C) Mutation rates are very low, and so recessive alleles are rare, which results in few recessive disease traits.
D) Most recessive mutations are lethal; as a result there are few recessive diseases.
E) Detrimental alleles are always being removed from a population due to natural selection.

Question 58

A population that goes through a dramatic reduction in size will experience:

A) an effective population size.
B) Hardy-Weinberg equilibrium.
C) a genetic rescue.
D) a genetic bottleneck.
E) inbreeding depression.

Question 59

Differential reproduction of genotypes leads to evolution via what process?

A) inbreeding
B) natural selection
C) genetic rescue
D) genetic drift
E) mutational load

Question 60

_____ occurs when one allele or trait is favored over another.

A) Directional selection
B) Mutation-selection equilibrium
C) Founder effects
D) Stabilizing selection
E) Overdominance

Question 61

A newspaper story on AIDS reports that an allele (R) confers complete resistance to HIV when homozygous and that 1% of the human population is resistant (RR). The story also states that 20% of the population carries one copy of the resistance allele (i.e., is heterozygous). Is this a guess, an approximation, or an exact frequency, assuming that the population is at Hardy-Weinberg equilibrium?

Question 62

Evolutionary biologists usually define population size using the effective population size rather than the census number. What is the effective population size and what factors can affect it?

Question 63

Huntington's disease is caused by a single dominant allele and results in progressive mental and neurological damage. The disease usually becomes 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's 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?

Question 64

You are studying a very large population of crocodiles on the Nile River in Africa and have identified a newly arisen (by mutation) allele at the C locus. The initial allelic frequency of the mutant allele c is 0.01. You have also determined that the allele acts additively. On a moonless night, you genotype nesting females and count the number of eggs they lay. You find that, on average, CC females produce 98 eggs, Cc females produce 99 eggs, and cc females produce 100 eggs. In this species of crocodile, all eggs hatch and survive to maturity.
a. Will the c allele increase, decrease, or stay the same in the next generation?
b. Will you likely be able to observe the change in the allelic frequency over the next couple of generations? Why?
c. In the long run, what will happen to the frequencies of the C and c alleles in this population?

Question 65

The fitness for a particular species of South American bats is determined by a single gene locus with two segregating alleles, (W) and (w), which determines echo-location ability. The dominant allele W causes normal echo-location, whereas the recessive allele w impairs echo-location ability. In the large bat population that you are studying, you determine initial frequencies of the W and w alleles to be 0.7 (p) and 0.3 (q), respectively. If the genotypes are in Hardy-Weinberg equilibrium on fertilization, and the selection coefficient (s) is 0.4, determine the effects of natural selection on the allelic frequencies after one generation.

Question 66

Huntington's disease is caused by a single dominant allele and results in progressive mental and neurological damage. The disease usually becomes 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's disease has not been associated with any other disease, now or in the past. Why might natural selection not have eliminated such a deleterious allele from the population?

A) Natural selection acts through reproduction, and most individuals with Huntington's disease reproduce prior to discovery.
B) Diseases tend to remain in populations because of heterozygous carriers.
C) Modern health care has acted as an agent against selection.
D) Natural selection tends not to work on human diseases and in human populations.
E) Natural selection only works on young individuals or newborns. Huntington's disease only works on older people.

Question 67

By the early 1980s, the population of Florida panthers had dwindled to fewer than 30. Furthermore, within this population was a high frequency of detrimental traits, including low sperm count and undescended testicles in males and kinked tails in both sexes. The future for this iconic population was bleak at best. Provide an explanation for the observed detrimental traits. Provide a possible solution that would both increase the likelihood that the population would survive and preserve the genetic identity of this unique population.

Question 68

By the early 1980s, the population of Florida panthers had dwindled to fewer than 30. Within this population, there was a high frequency of detrimental traits, including low sperm count and undescended testicles in males and kinked tails in both sexes. The future for this iconic population was bleak at best. Which of the following is the BEST solution that would both increase the likelihood that the population would survive and preserve the genetic identity of this unique population?

A) Genetic rescue, in which panthers from another population would be introduced in order to bring in new genetic variation and to reduce the genetic load.
B) The population could be removed and relocated to a better habitat, which should help the population recover.
C) Individuals with the genetic abnormalities could be removed from the population.
D) Some individuals could be moved so they will mate with specific other, healthier animals, which would assure more mixing of nondetrimental alleles.
E) There is no viable solution to saving this population.

Question 69

By the early 1980s, the population of Florida panthers had dwindled to fewer than 30. Within this population, there was a high frequency of detrimental traits, including low sperm count and undescended testicles in males and kinked tails in both sexes. The future for this iconic population was bleak at best. Which of the following provides the BEST explanation for the observed detrimental traits?

A) The mutation rate in this population is very high due to the small number of individuals.
B) Natural selection is acting in this population and resulting in more individuals with detrimental traits.
C) Migration of individuals into this population has introduced more detrimental traits.
D) The population is experiencing a genetic bottleneck, where the genetic variation is declining and harmful alleles are drifting to high frequencies.
E) Recurrent mutation and natural selection are acting as opposing forces on this population and an equilibrium has not yet been reached.