Deck 12: The Chromosomal Basis of Inheritance and DNA: The Genetic Material

Question 1

Suppose a new form of DNA polymerase III is discovered that does not require a primer to begin synthesis of a new strand. All other properties of the enzyme remain unchanged. If this new enzyme were to be expressed in the same organism that normally expresses DNA polymerase III, what would no longer be necessary to completely replicate all of the cellular DNA?

A) DNA polymerase I
B) Telomerase
C) DNA ligase
D) DNA helicase
E) Single-strand binding protein

Answer 1

DNA polymerase I

Question 2

Suppose a new species of bacteria was found that contained a form of DNA polymerase III that can add new nucleotides to either the 5' end or the 3' end of an existing strand. All other properties of the DNA polymerase III enzyme remain unchanged. In addition, these bacteria contain all of the other enzymes and proteins relevant to DNA synthesis that are found in E. coli. How would DNA replication in these new bacteria differ from replication in E. coli?

A) Both new strands could be synthesized continuously
B) Both new strands could be synthesized discontinuously
C) DNA pol I would no longer be required for replication
D) DNA ligase would no longer be required for replication

Answer 2

Both new strands could be synthesized continuously

Question 3

You decide to repeat the Meselson-Stahl experiment, except this time you plan to grow the cells on light ¹⁴N medium for many generations and then transfer them to heavy ¹⁵N medium and allow them to grow for 2 additional generations (2 rounds of DNA replication). If the conservative model of DNA replication is correct, what is the expected distribution of DNA in the density gradient after one round of replication?

A) One band of intermediate density
B) One band of light density
C) One band of heavy density
D) One band of light density and one band of heavy density
E) One band of light density and one band of intermediate density

Answer 3

One band of light density and one band of heavy density

Question 4

You decide to repeat the Meselson-Stahl experiment, except this time you plan to grow the cells on light ¹⁴N medium for many generations and then transfer them to heavy ¹⁵N medium and allow them to grow for 2 additional generations (2 rounds of DNA replication). If the semiconservative model of DNA replication is correct, what is the expected distribution of DNA in the density gradient after two rounds of replication?

A) One band of intermediate density
B) One band of intermediate density and one band of light density
C) One band of intermediate density and one band of heavy density
D) One band of heavy density and one band of light density
E) One band of heavy density

Question 5

You are working with a strain of E. coli that has a mutation in the DNA polymerase II gene, such that the encoded protein is exonuclease deficient, but is otherwise normal. How do you predict that this would most likely affect the activity of this enzyme?

A) This mutation would prevent the ability of DNA polymerase II to engage in lagging strand synthesis.
B) This mutation would prevent the ability of DNA polymerase II to form phosphodiester bonds between nucleotides.
C) This mutation would prevent the ability of DNA polymerase II to remove RNA nucleotides in the 5' to 3' direction.
D) This mutation would prevent the ability of DNA polymerase II to remove DNA nucleotides that are damaged.

Question 6

You are performing an experiment to study replication of DNA on a specific yeast chromosome. Yeast cells were synchronized in G1 and were released into S phase. DNA was recovered every five minutes after release into S phase, and an analysis was done to look for DNA replication in specific regions of the yeast chromosome. Assume that these regions of the yeast chromosome are adjacent to each other in the following order: Region A, Region B, Region C, Region D. The data below indicate the times during which DNA replication was observed in each of these regions. Using these data, which region or regions of the yeast chromosome most likely contained an origin of replication?
Times When DNA Replication Was Observed in Each Region:
Region A: 40 minutes, 45 minutes, and 50 minutes
Region B: 35 minutes, 40 minutes and 45 minutes
Region C: 30 minutes, 35 minutes, and 40 minutes
Region D: 35 minutes, 40 minutes, and 45 minutes

A) Region A
B) Region B
C) Region C
D) Region D
E) Regions A, B, C and D

Question 7

Each origin of replication in eukaryotic cells is recognized by an origin recognition complex, which allows the assembly of the pre-replicative complex including the replicative helicase. This complex ultimately allows the recruitment of DNA polymerase. After DNA polymerase is recruited to an origin and replicates the DNA in that region during S phase, the replicative helicase cannot be loaded onto the DNA in that region again until early G1 due to a variety of regulatory mechanisms. Why is it important that, once used, the replicative helicase cannot be loaded onto the DNA again until G1 of the cell cycle?

A) This ensures that multiple origins must be used to replicate the DNA in all cellular chromosomes.
B) This ensures that DNA cannot be replicated again in that region until the next cell cycle.
C) This ensures that telomeres on all chromosomes will be replicated properly.
D) This ensures that DNA repair processes can only take place during G1 of the cell cycle.

Question 8

A married couple has a son with sickle-cell disease. If this couple has more children, what is the likelihood that a daughter will inherit sickle-cell disease?

A) A daughter would be less likely to inherit sickle-cell disease than a son
B) A daughter would be more likely to inherit sickle-cell disease than a son
C) A daughter would be equally likely to inherit sickle-cell disease as compared to a son
D) A daughter cannot inherit sickle-cell disease, while a son can

Question 9

Huntington's disease is caused by a single dominant allele. It is a lethal disease, yet it persists in the human population. Which of the following statements best describes why?

A) Huntington's disease is sex-linked and every human has at least one X chromosome; thus, the chances are extremely high for this allele to be maintained in the human population.
B) Huntington's disease can present symptoms so mild that they appear to lack dominant expression of the allele in some individuals; in those cases, the allele is passed on to the offspring.
C) While lethal to a parent, Huntington's disease will not be lethal to the offspring since it can skip a generation.
D) Huntington's disease presents symptoms in mid-life, after most people have already had offspring.
E) Even though Huntington's disease is lethal, it improves chances for reproduction before the person dies.

Question 10

In humans, the male has an X and a Y sex chromosome. The human female has two X chromosomes. In birds, the female has a Z and a W sex chromosome while the male has two Z chromosomes. Which of the following statements is accurate about which parent determines the gender of the offspring?

A) In humans and birds, the male determines the gender of all the offspring.
B) In humans and birds, the female determines the gender of all the offspring.
C) In humans, the male determines the gender of the offspring, and in birds the female determines the gender.
D) In humans, the female determines the gender of the offspring, and in birds the male determines the gender.
E) Determination of the gender of any human or bird offspring is related to the environmental conditions at the time of conception.

Question 11

In some species, sex determination is influenced by environmental temperature during development. If you wanted to determine the temperature at which one would obtain a 1:1 sex ratio in a particular species of turtle, which of the following experiments would best address this question?

A) Grow the turtles in two different incubators at temperatures of 22ºC and 30ºC.
B) Grow the turtles in three different incubators at temperatures of 26ºC, 28ºC, and 30ºC.
C) Grow the turtles in four different incubators at temperatures of 24ºC, 26ºC, 28ºC, and 30ºC.
D) Grow the turtles in five different incubators at temperatures of 22ºC, 24ºC, 26ºC, 28ºC, and 30ºC.

Question 12

Assuming no chromosomal aneuploidies, a calico cat would be which gender?

A) Female
B) Male
C) Cannot be determined

Question 13

In Drosophila, dosage compensation is controlled by the male-specific lethal (MSL) complex consisting of MSL proteins and roX RNAs. Based on what you know about dosage compensation, the role of the MSL complex in males would be to

A) double the level of expression of genes on the X chromosome.
B) increase the level of expression of genes on the X chromosome by 50%.
C) decrease the level of expression of genes on the X chromosome by 50%.
D) decrease the level of expression of genes on the X chromosome by 100%.
E) double the level of expression of genes on the Y chromosome.

Question 14

What is the relationship between recombination frequency and the actual physical distance on a chromosome?

A) As physical distance increases, the recombination frequency increases in a linear fashion.
B) As physical distance increases, the recombination frequency decreases in a linear fashion.
C) As physical distance increases, the recombination frequency first increases in a linear fashion, but gradually levels off to a frequency of 0.5.
D) As physical distance increases, the recombination frequency first increases, but then decreases.

Question 15

In some human populations, the proportion of individuals who are heterozygous for the sickle cell allele is much higher than would be expected by chance alone. Why?

A) Individuals with two normal alleles have an advantage over heterozygous individuals.
B) Individuals with two harmful alleles have an advantage over heterozygous individuals.
C) Individuals with two harmful alleles have an advantage over individuals with two normal alleles.
D) Heterozygous individuals have an advantage over individuals with two normal alleles.

Question 16

How did the development of anonymous markers aid in the production of a human genetic map?

A) Anonymous markers are genetic markers that do not cause a detectable phenotype, but can be detected by molecular techniques. The markers correspond to specific and unique chromosomal regions, thereby allowing for the identification and ordering of particular segments of DNA. Such information was essential to the generation of a human genetic map.
B) Anonymous markers are genetic markers that cause a detectable phenotype and can't be detected by molecular techniques. The markers correspond to specific and unique chromosomal regions, thereby allowing for the identification and ordering of particular segments of DNA. Such information was essential to the generation of a human genetic map.
C) Anonymous markers are genetic markers that do not cause a detectable phenotype, but can be detected by molecular techniques. The markers correspond to specific and unique genetic regions, thereby allowing for the identification and ordering of particular segments of the chromosome. Such information was essential to the generation of a human genetic map.

Question 17

Why isn't mitochondrial DNA a unique identifier?

A) Mitochondrial DNA is inherited through the paternal lineage. All offspring inherit their father's mitochondria, and therefore the same mitochondrial DNA. As a result, all family members that share a paternal lineage would have the same mitochondrial DNA. Mitochondrial DNA can therefore be used to confirm or eliminate a person's relationship within a paternal line, but cannot be used to identify a specific individual.
B) Mitochondrial DNA is inherited through the maternal lineage. All offspring inherit their mother's mitochondria, and therefore the same mitochondrial DNA. As a result, all family members that share a maternal lineage would have the same mitochondrial DNA. Mitochondrial DNA can therefore be used to confirm or eliminate a person's relationship within a maternal line, but cannot be used to identify a specific individual.
C) Mitochondrial DNA is inherited through the maternal lineage. All female offspring inherit their mother's mitochondria, and therefore the same mitochondrial DNA. As a result, all female family members that share a maternal lineage would have the same mitochondrial DNA. Mitochondrial DNA can therefore be used to confirm or eliminate a person's relationship within a maternal line, but cannot be used to identify a specific individual.

Question 18

In the fruit fly Drosophila, there is a dominant gene for normal wings and its recessive allele for vestigial wings. At another gene locus on the same chromosome, there is a dominant gene for red eyes and its recessive allele for purple eyes. A male that was heterozygous at both gene loci was mated with a female that was homozygous for both recessive alleles and the following results were observed among the offspring:
Normal wings and red eyes - 420
Vestigial wings and red eyes - 80
Normal wings and purple eyes - 70
Vestigial wings and purple eyes - 430
According to these data, what is the distance, in centimorgans, between these 2 gene loci? (Enter the number only without the units. For example, 100 cM would be entered as 100)

Question 19

At an autosomal gene locus in humans, the allele for brown eyes is dominant over the allele for blue eyes. At another gene locus, located on the X chromosome, a recessive allele produces colorblindness while the dominant allele produces normal color vision. A heterozygous brown-eyed woman who is a carrier of colorblindness marries a blue-eyed man who is not colorblind. What is the probability that their first child will be a blue-eyed female who has normal color vision? (Enter the probability as a percent. Enter the number only without the percent sign. For example, enter 100% as 100 and enter 12.5% as 12.5)

Question 20

At an autosomal gene locus in humans, the allele for brown eyes is dominant over the allele for blue eyes. At another gene locus, located on the X chromosome, a recessive allele produces colorblindness while the dominant allele produces normal color vision. A heterozygous brown-eyed woman who is a carrier of colorblindness marries a blue-eyed man who is not colorblind. The woman becomes pregnant and an ultrasound test shows that the child is a girl. What is the probability that she will be colorblind? (Enter the probability as a percent. Enter the number only without the percent sign. For example, enter 100% as 100 and enter 12.5% as 12.5)

Question 21

Suppose you are carrying out a series of crosses with an insect where the mechanism of sex determination is unknown. You discover a mutant female with short bristles and decide to cross it with a wild type male that has normal bristles. Half of the F₁ progeny have short bristles but all of these short-bristled F₁ progeny are males. Based on these results, a valid hypothesis would be

A) Males are ZW, females are ZZ, and short bristles are caused by a dominant allele on the Z chromosome
B) Males are ZZ, females are ZW, and short bristles are caused by a recessive allele on the Z chromosome
C) Males are ZZ, females are ZW, and short bristles are caused by a dominant allele on the W chromosome
D) Males are ZZ, females are ZW, and short bristles are caused by a dominant allele on the Z chromosome

Question 22

In 1910, Morgan did a series of experiments with the fruit fly Drosophila, an organism where females are XX and males are XY. When a mutant male fly with white eyes was crossed with a wild type female with red eyes, none of the F₁ progeny had white eyes but 18% of the F₂ progeny had white eyes. Unexpectedly, all of these white-eyed F₂ flies were males. Based on these results, Morgan concluded that white eyes is caused by a recessive X-linked allele. Suppose Morgan has found that half of the F₁ progeny had white eyes but all of these white-eyed F₁ flies were females. In this case, a valid hypothesis would be

A) White eyes is caused by a recessive Y-linked allele
B) White eyes is caused by a dominant Y-linked allele
C) White eyes is caused by a dominant X-linked allele
D) White eyes is caused by a dominant autosomal allele

Question 23

In humans, red-green color blindness is caused by a recessive allele on the X chromosome. Therefore, if a female who is a carrier for the allele that causes color blindness marries a male who is color blind, the probability that their first child will be a girl who is color blind is 25%. This assumes normal dosage compensation where the X that is inactivated in females varies randomly from cell to cell. But suppose the normal mechanism of dosage compensation is altered so that the X that is inactivated in any given female is random but the same X is inactivated in every cell of her body. In this case, what is the probability that their first child would be a girl with color blindness? ( Express the probability as a percent. Enter the number only without the percent sign. For example, enter 100% as 100 and enter 12.5% as 12.5 )

Question 24

Genetic maps are based on recombination frequencies. Because both odd and even numbers of crossovers can occur between any 2 gene loci, as the physical distance between two loci increases, the maximum recombination frequency levels off at 50%. However, suppose you discovered a species where only an even number of crossovers can occur between any two gene loci. In this case, as the physical distance between two loci increases, you would expect the maximum recombination frequency to

A) remain at zero
B) increase with no limit
C) level off at 25%
D) level off at 75%
E) level off at 100%

Question 25

Below is a pedigree for a particular human trait. Affected individuals are illustrated by the shaded in circles or squares. This particular pedigree does not yet have a particular shading pattern for carriers. As a result, some of these individuals may be carriers for the trait. What is the mechanism of inheritance of this trait?

A) Sex-linked recessive
B) Autosomal dominant
C) Autosomal recessive
D) Mitochondrial