UNIT 5 MCQ ap classroom

In humans, one allele of the APOE gene, called APOE–ε2, can result in a high tolerance of cholesterol. Cholesterol is a vital substance for humans but may lead to heart disease in an older adult with a history of high cholesterol diets. High cholesterol diets are becoming more prevalent in the United States. Currently only about 2% of humans carry the APOE–ε2 allele.

Which of the following states a valid null hypothesis about the future distribution of APOE alleles in future generations in the United States?

The variant protects an individual from a condition that is only common among humans beyond reproductive age, so the frequency of the allele will likely not change much in the future because it is not influenced by natural selection.

Students observed the distribution of different color phenotypes in northern ravine salamanders (Plethodon electromorphus) before and after a spring flood. The data are shown in Table 1.

Table 1. Observed number of salamanders by phenotype before and after a spring flood

	Salamander Distribution before the Flood (n)	Salamander Distribution after the Flood (n)
Black phenotype	13	7
Dark-brown phenotype	25	14
Light-brown phenotype	6	3

Which of the following is an appropriate null hypothesis regarding the phenotypic frequencies of this population of salamanders before and after the flood?

The proportions of black, dark-brown, and light-brown salamanders before and after the flood are not significantly different, and any observed differences are due to random chance.

The California newt, Taricha torosa, lives in the coastal areas around Los Angeles. Which of the following is a valid null hypothesis relating fitness to survival of a bottleneck event in a coastal area where a small, isolated population of California newts resides?

Surviving the bottleneck event will be random, so any change in the allelic frequencies of the salamander population is not attributed to fitness.

A gene that influences coat color in domestic cats is located on the X chromosome. A female cat that is heterozygous for the gene (XBXO) has a calico-colored coat. In a genetics experiment, researchers mate a calico-colored female cat (XBXO) with an orange-colored male cat (XOY) to produce an F1 generation. The researchers record observations for the cats in the F1 generation and plan to use the data to perform a chi-square goodness-of-fit test for a model of X-linked inheritance. The data for the chi-square goodness-of-fit test are presented in Table 1.

Table 1. Data for the chi-square goodness-of-fit test

			PhenotypeGenotypeObservedExpected
Calico-colored female	XBXO	15	10
Orange-colored female	XOXO	6	10
Black-colored male	XBY	11	10
Orange-colored male	XOY	8	10

The researchers calculate a chi-square value of 4.6 and choose a significance level of p=0.05. Which of the following statements best completes the chi-square goodness-of-fit test?

The null hypothesis cannot be rejected because the chi-square value is less than the critical value.

In order to determine the effects of age on the accumulation of mitochondrial mutations, mitochondrial DNA samples from young mice (3 months) and old mice (30 months) were observed for mutations.

Table 1. Number of mitochondrial mutations in 106 base pairs

		MouseYoungOld
A	1
B	1
C	3
D	2
E	4
F		10
G		15
H		12
I		9
J		11

Which of the following is a correct analysis of this data set?

There is an increase in the mean number of mutations for the two age groups of 9.2 mutations per 106 base pairs. This is more critical in female mammals since mitochondria are maternally inherited.

An experiment was performed to determine the mode of inheritance of two mouse genes, one for fur color and one for fur length. It is known that black fur (B) is dominant over white fur (b) and that long fur (L) is dominant over short fur (l). To determine how the genes are inherited, a cross was performed between two true-breeding mice, one with long black fur and one with short white fur. Their progeny, the F1 generation, all had long black fur. Five F1 male-female pairs were then crossed with one another. The F2 generation phenotypes for each cross are shown in Table·1.

Table 1. Number of F2 generation phenotypes for five crosses

					PhenotypeCross 1Cross 2Cross 3Cross 4Cross 5
Long black fur	6	5	5	6	7
Long white fur	1	1	0	2	2
Short black fur	0	2	1	1	1
Short white fur	2	3	3	2	2

Which of the following is the mean number per cross of F2 generation offspring that are the result of crossing over?

2.2

Pigeons demonstrate ZW sex determination, such that a ZZ genotype produces a male and a ZW genotype produces a female. The gene for feather color is located on the Z chromosome, and the red allele is dominant over the brown allele. Three crosses between brown male pigeons and red female pigeons were performed, and the results are shown below.

Table 1. Offspring from three separate crosses of a brown male pigeon and a red female pigeon

	Number of Offspring
Phenotype	Cross 1	Cross 2	Cross 3
Red	11	9	7
Brown	9	11	13

9

In fruit flies, sepia eyes and ebony body are traits that display autosomal recessive patterns of inheritance. To investigate whether the traits are genetically linked, students cross wild-type flies with a line of flies that have sepia eyes and ebony bodies. The students observe that all the flies in the F1 generation have normal eyes and normal bodies. The students allow the flies in the F1 generation to mate and produce an F2 generation. The students then record observations for the flies in the F2 generation and use the data to perform a chi-square goodness-of-fit test for a model of independent assortment. The setup for the chi-square goodness-of-fit test is presented in Table 1.

Table 1. Setup for the students’ chi-square goodness-of-fit test

		PhenotypeObservedExpected
Normal eyes, normal body	231	279
Normal eyes, ebony body	86	93
Sepia eyes, normal body	97	93
Sepia eyes, ebony body	82	31

The students calculate a chi-squared value of 92.86 and compare it with a critical value of 7.82. Which of the following best completes the chi-square goodness-of-fit test?

Responses

The null hypothesis can be rejected, and the students should conclude that the data may have resulted from genetic linkage.

A student carries out a genetics experiment with fruit flies to investigate the inheritance pattern of the white eye trait. The student crosses a homozygous white-eyed female with a wild-type male and records observations about the flies in the F1 generation. The student plans to use the F1 data to perform a chi-square goodness-of-fit test for a model based on an X-linked recessive pattern of inheritance. The student will use one degree of freedom and a significance level of p=0.05. The setup for the student’s chi-square goodness-of-fit test is presented in Table 1.

Table 1. Setup for the student’s chi-square goodness-of-fit test

Phenotype	Observed	Expected
Red-eyed female	53	50
White-eyed male	47	50

The student calculates a chi-square value of 0.36. Which of the following statements best completes the student’s chi-square goodness-of-fit test?

The critical value is 3.84, and the student cannot reject the null hypothesis.

The Russian blue is a rare breed of cat that is susceptible to developing cataracts on the eyes. Scientists hypothesize that this condition is inherited as a result of a mutation. Figure 1 shows a pedigree obtained in a study of cats owned by members of the Russian Blue Club in Sweden.

Figure 1. Pedigree of Russian blue cats owned by Russian Blue Club

Based on the inheritance pattern shown in Figure 1, which of the following best predicts the nature of the original mutation?

A recessive mutation on a somatic chromosome

In sweet pea plants, purple flower color is dominant over red flower color and long pollen grain shape is dominant over round pollen grain shape. Two sweet pea plants that are heterozygous for both flower color and pollen grain shape are crossed with one another. A geneticist is surprised to observe that there are far fewer round, purple offspring and long, red offspring than were predicted by the 9:3:3:1 expected phenotypic ratio.

Which of the following statements provides the most reasonable prediction to account for the deviation from the expected results?

In sweet pea plants, the gene for flower color and the gene for pollen grain shape are genetically linked.

Insulin is a hormone produced by some pancreatic cells. Scientists have isolated the DNA sequence that codes for human insulin production.

Which of the following best predicts the effect of inserting this gene into the DNA of a bacterial cell?

The recombinant bacterium will produce human insulin using its own transcription and translation machinery.

A student crosses a pure-breeding line of red-flowered poinsettias with a pure-breeding line of white-flowered poinsettias. The student observes that all the plants in the F1 generation have pink flowers. The student then crosses the F1 plants with one another and records observations about the plants in the F2 generation. The student will use the F2 data to perform a chi-square goodness-of-fit test for a model of incomplete dominance. The setup for the student’s chi-square goodness-of-fit test is presented in Table 1.

Table 1. A chi-square goodness-of-fit test for incomplete dominance

Phenotype	Observed	Expected
Red flowers	64	56
Pink flowers	107	112
White flowers	53	56

The critical value for a chi-square test with a significance level of p=0.05 and 2 degrees of freedom is 5.99. Which of the following statements best completes the student’s chi-square goodness-of-fit test?

The calculated chi-square value is 1.53, and the null hypothesis cannot be rejected.

In fruit flies, purple eyes and ebony body are traits that display autosomal recessive patterns of inheritance. In a genetics experiment, students cross wild-type flies with flies that have purple eyes and ebony bodies. The students observe that all the flies in the F1 generation have normal eyes and a normal body color. The students then allow the F1 flies to mate and produce an F2 generation. The students record observations about the flies in the F2 generation and use the data to perform a chi-square goodness-of-fit test for a model of independent assortment. The setup for the students’ chi-square goodness-of-fit test is presented in Table 1.

Table 1. The students’ chi-square goodness-of-fit test for a model of independent assortment

Phenotype	Observed	Expected
Normal eyes, normal body	187	171
Normal eyes, ebony body	49	57
Purple eyes, normal body	41	57
Purple eyes, ebony body	27	19

The students choose a significance level of p=0.01. Which of the following statements best completes the next step of the chi-square goodness-of-fit test?

The calculated chi-square value is 10.48, and the critical value is 11.35.

In a strain of tomato plants, short plant height and small fruit size are traits that display autosomal recessive patterns of inheritance. To investigate whether the traits segregate independently, researchers cross a pure-breeding line of tall tomato plants that have large fruits with a pure-breeding line of short tomato plants that have small fruits. The researchers observe that all the plants in the F1 generation are tall and have large fruits. The researchers cross the F1 plants with one another to generate an F2 generation. The researchers record observations for the F2 generation and will use the data to perform a chi-square goodness-of-fit test for a model of independent assortment. The setup for the chi-square goodness-of-fit test is shown in Table 1.

Table 1. Observed and expected counts of tomato plants in the F2 generation

Phenotype	Observed	Expected
Tall plant with large fruits	104	90
Tall plant with small fruits	17	30
Short plant with large fruits	26	30
Short plant with small fruits	13	10

The researchers choose a significance level of p=0.05. Which of the following best completes the chi-square goodness-of-fit test?

The calculated chi-square value is 9.24, and the critical value is 7.82. The null hypothesis of independent assortment can be rejected.

Table 1 shows the stage and number of cells and chromosomes per cell at the end of the stage in a 2n=24 organism.

Table 1. Cell and chromosome count during selected phases of meiosis

		StageNumber of CellsNumber of Chromosomes per Cell
Prophase I	1	24
Metaphase I	1	24
Anaphase I	1	24
Telophase I	1	24
Beginning of Prophase II	2	12

Which of the following statements correctly describes the chromosomes in each daughter cell at the end of meiosis I?

Each daughter cell contains 12 chromosomes, each composed of two chromatids. Each chromosome is one of a pair of homologous chromosomes from the parent cell, with the other homologue found in the other daughter cell.

Both mitosis and meiosis begin with a parent cell that is diploid. Which of the following best describes how mitosis and meiosis result in daughter cells with different numbers of chromosomes?

Mitosis produces two identical diploid daughter cells after one round of division. Meiosis produces four haploid daughter cells after two rounds of division.

Saccharomyces cerevisiae is a diploid yeast species that can reproduce either sexually or asexually. An experiment was performed to induce mitotically dividing S. cerevisiae cells in G2 to undergo meiosis. Which of the following best describes the steps these cells will follow to form gametes?

The first division will reduce the number of chromosomes by half for each daughter cell, and the second division will move single chromatids to each daughter cell.

Scientists have found that DNA methylation suppresses crossing-over in the fungus Ascobolus immersus. Which of the following questions is most appropriately raised by this specific observation?

Is the level of genetic variation in the gametes related to the amount of DNA methylation observed?

Figure 1. Model of crossing over between homologous chromosomes, indicating crossing over rate of selected loci.

During prophase I replicated homologous chromosomes pair up and undergo synapsis. What testable question is generated regarding synapsis and genetic variability by Figure 1 ?

Is the distance between two gene loci related to crossover rate?

A model showing two possible arrangements of chromosomes during meiosis is shown in Figure 1.

Figure 1. Two possible arrangements of chromosomes during meiosis

Which of the following questions about genetic diversity could most appropriately be answered by analysis of the model in Figure 1 ?

Responses

How does the independent assortment of the two sets of homologous chromosomes increase genetic diversity?

In eastern gray squirrels, Sciurus carolinensis, the allele for black fur (B) is dominant to the allele for gray fur (b). In a particular population of gray squirrels, 64% have black fur and 36% have gray fur. A researcher calculated the allelic frequencies to be B=0.4 and b=0.6. Five years later, the researcher returned to the location and determined the allelic frequencies within the squirrel population to be B=0.6 and b=0.4.

Which of the following could best explain the increase in the frequency of the B allele in the population after five years?

The frequency of the B allele increased due to the selective pressures of the environment.

Gaucher disease type 1 (GD1) is a recessive genetic disease that affects 1 in 900 individuals in a particular population. GD1 is caused by a mutation in the enzyme glucocerebrosidase.

Assuming the population is in Hardy-Weinberg equilibrium, calculate the frequency of the wild-type (nonmutant) allele for the enzyme glucocerebrosidase.

Responses

0.967

In a long‑term study of a population of gray squirrels, researchers observed that most of the squirrels had gray fur. However, there were some individuals in the population with white fur (albino). Genetic analysis revealed that the albino condition is expressed by individuals who are homozygous recessive (gg). Over a ten-year period, the average frequency of albino squirrels in the population was 0.18. If the population is assumed to be in Hardy-Weinberg equilibrium, the average frequency of the dominant allele is closest to which of the following?

Responses

0.58

In a large, isolated population of an insect species, a specific gene locus has one dominant allele (A) and one recessive allele (a). The genotype frequencies of the gene were collected for ten generations, as shown in Table 1.

Table 1. Genotypic frequencies over ten generations in an insect species

	AA	Aa	aa
Generation 1	0.47	0.43	0.10
Generation 5	0.32	0.60	0.08
Generation 10	0.20	0.75	0.05

Which of the following could best account for the change in genotypic frequencies over the ten generations?

The population is not exhibiting random mating between individuals.

Which of the following statements best explains how a condition of Hardy-Weinberg equilibrium results in a population that exhibits stable allele frequencies (i.e., a nonevolving population) ?

Without migration or mutation, new alleles cannot be introduced to the population.

Humans vary in their ability to taste the bitter chemical compound phenylthiocarbamide (PTC). The taster phenotype is dominant to the nontaster phenotype. Researchers tested the PTC taster phenotype of individuals from an isolated population. In the sample, 780 individuals were able to taste PTC and 70 individuals were not able to taste PTC.

Assuming the population is in Hardy-Weinberg equilibrium, what is the frequency of the non-taster allele?

0.29

An African violet grower observes that genetically identical African violet plants growing near the walls of the greenhouse have white flowers, that plants growing farther away from the walls have pale blue flowers, and that plants growing nearest the center of the greenhouse have dark blue flowers.

Which of the following best explains the differences in flower color of the African violets in the greenhouse?

An enzyme responsible for flower color does not fold correctly in cooler temperatures, and the greenhouse is warmest in the center.

A scientist studying phenotypic variation in a species of butterfly observed that genetically identical caterpillars grown in similar cages but exposed to different colored lights developed into butterflies with differences in wing color and body size, as shown in Table 1.

Table 1. Effect of Exposing Identical Caterpillars to Specific Colors of Light

		Phenotype of Adult ButterflyCaterpillars Exposed to Red LightCaterpillars Exposed to Blue Light
Wing color	Darker	Lighter
Body size	Smaller	Larger

Which of the following best explains the cause of the phenotypic variation observed in the butterflies?

There was differential gene expression of wing color and body size in response to the colors of light the caterpillars were exposed to.

Australian dragon lizards have a ZW sex-determination system. The male genotype is homogametic (ZZ), and the female genotype is heterogametic (ZW). However, all eggs incubated at temperatures above 32°C tend to develop into females.

Which of the following best explains how the development of phenotypic female Australian dragon lizards with a ZZ genotype occurs when incubation temperatures are above 32°C?

Incubation temperatures above 32°C inhibit the genes on the Z chromosome that produce proteins necessary for male development.