Deck 15: Linkage and Chromosomes

Question 1

A man with normal vision who is a dwarf due to achondroplasia has children with a woman who is colorblind and of average height. Dwarfism caused by achondroplasia is autosomal dominant, and red-green color blindness is X-linked recessive. What proportion of their sons are expected to be color blind and of normal height?

A) 0
B) 1/2
C) 1/4
D) all

Answer 1

B

Question 2

Glucose-6-phosphate dehydrogenase deficiency (G6PD) is inherited as an X-linked recessive allele in humans. A woman whose father had G6PD is planning a family with a man who has no history of the disease. What proportion of their sons are expected to have the disease?

A) 100%
B) 1/4
C) 1/2
D) 0

Answer 2

C

Question 3

Which of the following events results in X-inactivation in female mammals?

A) activation of the XIST gene on the X chromosome that will become the Barr body
B) activation of the BARR gene on one X chromosome, which then becomes inactive
C) inactivation of the XIST gene on the X chromosome derived from the male parent
D) attachment of methyl (-CH3) groups to the X chromosome that will remain active

Answer 3

A

Question 4

A man with normal vision who is a dwarf due to achondroplasia has children with a woman with colorblindness who is of average height. Dwarfism caused by achondroplasia is autosomal dominant, and red-green color blindness is X-linked recessive. What proportion of their daughters are expected to be color-blind with achondroplasia?

A) 0
B) 1/2
C) 1/4
D) 3/4

Question 5

In humans, clear sex differentiation does not occur at fertilization. It becomes evident after the second month of gestation. Which of the following statements describes the first event of sex differentiation in human embryos?

A) production of testosterone in male embryos
B) production of estrogens in female embryos
C) activation of SRY in male embryos and masculinization of the gonads
D) activation of SRY in females and feminization of the gonads

Question 6

In birds, sex is determined by ZW chromosome inheritance. Males are ZZ and females are ZW. Within pigeon populations there is a recessive, Z-linked allele that is lethal in embryos. What is the expected sex ratio in the offspring of a cross between a male that is heterozygous for the lethal allele and a wildtype female?

A) 2:1 male to female
B) 1:2 male to female
C) 1:1 male to female
D) 3:1 male to female

Question 7

In cats, an X-linked locus is responsible for fur color. There are two known alleles at this locus. One results in black fur color; the other results in orange fur color. A heterozygote animal has patches of orange and black fur (tortoiseshell). Which coat color phenotypes are expected from the cross of a black female and an orange male?

A) tortoiseshell females; tortoiseshell males
B) black females; orange males
C) tortoiseshell females; black males
D) orange females; black males

Question 8

The SRY gene is best described as ________.

A) a gene present on the X chromosome whose product regulates female development
B) an autosomal gene whose product is required for the expression of genes on the Y chromosome
C) a gene present on the Y chromosome whose product regulates male development
D) an autosomal gene that whose product is required for the expression of genes on the X chromosome

Question 9

Cinnabar eye color is an X-linked, recessive characteristic in fruit flies. If a female having cinnabar eyes is crossed with a male having wild-type, red eyes, what percent of the F1 males will have cinnabar eyes?

A) 0%
B) 25%
C) 50%
D) 100%

Question 10

A recessive allele on the X chromosome is responsible for red-green color blindness in humans. A woman with normal vision whose father is color blind has children with a color-blind male. What is the probability that this couple's first son will be color blind?

A) 1/4
B) 1/2
C) 2/3
D) 3/4

Question 11

When Thomas Hunt Morgan crossed red-eyed F1 generation flies to each other, the F2 generation included both red- and white-eyed flies, but all the white-eyed flies were male. Which of these best explains Morgan's result?

A) The gene involved is located on the Y chromosome.
B) The gene involved is located on the X chromosome.
C) The gene involved is located on an autosome, but only in males.
D) Other male-specific factors influence eye color in flies.

Question 12

Use the following information to answer the question. In a Drosophila experiment, a homozygous wild-type female was crossed with a yellow-bodied male. All of the resulting F1 flies were phenotypically wild type. Crossing the F1 flies resulted in F2 flies having the characteristics shown in the figure. Which of the following statements best describes the yellow body allele?

A) It is recessive.
B) It is codominant.
C) It is dominant.
D) It is incompletely dominant.

Question 13

Which of the following individuals will inherit an X-linked allele from a male parent who carries the allele?

A) all of his daughters
B) half of his daughters
C) all of his sons
D) all of his children

Question 14

Duchenne muscular dystrophy is a serious condition caused by a recessive allele of a gene on the human X chromosome. The patients' muscles weaken over time because they have a lack or decreased levels of dystrophin, a muscle protein. Which of the following correctly predicts the probability of muscular dystrophy in female children?

A) Females can never have this condition.
B) One-fourth of the daughters of an affected man would have this condition.
C) One-half of the daughters of an affected man and a carrier woman would have this condition.
D) One-half of the daughters of an unaffected man and a carrier woman would have this condition.

Question 15

Red-green color blindness is an X-linked recessive trait in humans. Two people with normal color vision have a son with colorblindness. Given this information, the genotypes of the parents are ________.

A) XnXn and XnY
B) XNXN and XnY
C) XNXN and XNY
D) XNXn and XNY

Question 16

Males are more often affected by X-linked traits than are females because ________.

A) imprinting is more likely to occur on X chromosomes inherited from the mother than on Y chromosomes inherited from the father
B) X inactivation occurring in male effectively shuts down expression of any X chromosome genes
C) X chromosomes in males generally have more mutations than X chromosomes in females
D) males are hemizygous genes on the X chromosomes

Question 17

In cats, an X-linked locus is responsible for fur color. There are two known alleles at this locus. One results in black fur color; the other results in orange color. A heterozygote animal has patches of orange and black fur (tortoiseshell). Which of the following outcomes represents all of the possible offspring from the cross provided. Assume all cats have two sex chromosomes.

A) A
B) B
C) C
D) D

Question 18

In cats, an X-linked locus is responsible for fur color. There are two known alleles at this locus. One results in black fur color; the other results in orange fur color. A heterozygote animal has patches of orange and black fur (tortoiseshell). Which of the following explains the patches of color in female heterozygote cats?

A) Incomplete dominance of the black fur color allele
B) Fur color is codominant at the organism level
C) Imprinting at the fur color locus
D) Random X inactivation affects fur color

Question 19

Which of the following statements correctly describes the chromosome theory of inheritance as it was understood in the early 20th century?

A) Individuals inherit particular chromosomes attached to genes.
B) Mendelian genes are at specific loci on the chromosome and, in turn, segregate during meiosis.
C) No more than a single pair of chromosomes can be found in a healthy normal cell.
D) Natural selection acts on certain chromosome combinations rather than on genes.

Question 20

Male sex determination in mammals is in large part due to the SRY gene found on the Y chromosome. Which of the following scenarios will result in a person with an XX karyotype developing a male phenotype?

A) the loss of the SRY gene from an autosome during gamete formation
B) translocation of SRY to an X chromosome during gamete formation
C) the presence of an extra autosomal chromosome after fertilization
D) nondisjunction of the X chromosome during meiosis

Question 21

In Drosophila melanogaster, wing-size and body-color genes are linked. Vestigial wings and black body color are both recessive traits. A researcher crossed black-bodied, normal-winged females and gray-bodied, vestigial-winged males. The F1 were all gray bodied, normal winged. A test cross was performed with F1 females. The researcher calculated a map distance of 17 map units. Which of the following information is correct about the testcross progeny?

A) black-bodied, normal-winged flies = 17% of the total
B) black-bodied, normal-winged flies plus gray-bodied, vestigial-winged flies = 17% of the total
C) gray-bodied, normal-winged flies plus black-bodied, vestigial-winged flies = 17% of the total
D) black-bodied, vestigial-winged flies = 17% of the total

Question 22

Which of the following statements regarding gene linkage is correct?

A) The closer two genes are on a chromosome, the lower the probability that a crossover will occur between them.
B) The observed frequency of recombination of two genes that are far apart from each other has a maximum value of 100%.
C) Unlinked genes do not follow the law of equal segregation.
D) Linked genes are found on different chromosomes.

Question 23

Use the following information to answer the question.
A plantlike species on the hypothetical planet Pandora has three genetic traits: leaf color, controlled by gene L; a stem texture, controlled by gene S; and root length controlled by gene R. Each of the three genes has two alleles. The three genes are linked and recombine.
A geneticist performed a testcross with an organism of that species that is heterozygous for the three traits. She recorded progeny with the following phenotypic distribution:

Assuming that genetic inheritance for this hypothetical plant functions the same as on Earth, the parents in this cross most likely have the same phenotypes as which of the following progeny?

A) 2 and 5
B) 1 and 6
C) 4 and 8
D) 3 and 7

Question 24

Which of the following reasons explains why map units on a chromosome linkage map are not reliable measures of physical distances?

A) The frequency of crossing over varies along the length of the chromosome.
B) The relationship between recombination frequency and map units is different in every individual.
C) Physical distances between genes change during the course of the cell cycle.
D) The gene order on the chromosomes is slightly different in every individual.

Question 25

A testcross performed with F1 dihybrid flies results in more parental-type offspring than recombinant-type offspring. Which of the following statements best explains this result?

A) The two genes are linked on the same chromosome.
B) The two genes are linked but on different chromosomes.
C) Recombination did not occur in the cell during meiosis.
D) Both of the characters are controlled by more than one gene.

Question 26

Use the following information to answer the question. In a Drosophila experiment a homozygous wild-type female was crossed with a yellow-bodied male. All of the resulting F1 flies were phenotypically wild type. Crossing the F1 flies resulted in F2 flies having the characteristics shown in the figure. Which of the following statements best describes the location of the yellow body locus?

A) It is on an autosome.
B) It is X-linked.
C) It is inherited by X inactivation.
D) It is Y-linked.

Question 27

Use the diagram of six loci on a chromosome to answer the question. Locus Y is six map units from Locus X.
When attempting to map the location of Gene Q, relative to Locus Y and Locus Y, two testcrosses were performed and the following data collected.
Number of offspring

These data narrow the possible location of Gene Q to which of the following choices?

A) Locus # only
B) Locus $ only
C) Locus # or Locus *
D) Locus $ or Locus @

Question 28

A homozygous tomato plant with red fruit and yellow flowers was crossed with a homozygous tomato plant with golden fruit and white flowers. The F1 had red fruit and yellow flowers. F1 plants were testcrossed (crossing them to homozygous recessive individuals), and the following offspring were obtained:
Red fruit and yellow flowers-41
Red fruit and white flowers-7
Golden fruit and yellow flowers-8
Golden fruit and white flowers-44
How many map units separate these genes?

A) 17.6
B) 15
C) 17.1
D) The genes are on different (non-homologous) chromosomes

Question 29

A recombination frequency of 50% indicates ________.

A) the two genes are likely to be located on different chromosomes
B) all of the offspring have combinations of traits that match one of the two parents
C) the genes are located on sex chromosomes
D) the two genes are five map units apart

Question 30

Which of the following statements explains the observation that closely linked genes are typically inherited together?

A) The genes are located close together on the same chromosome.
B) The genes undergo nondisjunction in either meiosis I or meiosis II.
C) Alleles are paired together during meiosis.
D) Crossing over between identical copies can't be detected because it regenerates the original genotype.

Question 31

Use the following information to answer the question.
A plantlike organism on the hypothetical planet Pandora has three genetic traits: leaf color, controlled by gene L; a stem texture, controlled by gene S; and root length controlled by gene R. The three genes are linked and recombine.
A geneticist performed a testcross with a strain of the organism that is heterozygous for the three traits. She recorded progeny with the following phenotypic distribution:

Which of the progeny phenotypes will require recombination between genes L and S?

A) 1, 2, 5, and 6
B) 1, 3, 6, and 7
C) 2, 4, 5, and 8
D) 2, 3, 5, and 7

Question 32

The chromosomal alteration that results from a chromosome fragment joined to a nonhomologous chromosome is called a ________.

A) deletion
B) inversion
C) translocation
D) duplication

Question 33

Which of the following phrases correctly defines one genetic map unit?

A) the physical distance between any two linked genes
B) the physical distance between two genes that results in a 1% frequency of recombination
C) one nanometer of distance between two genes
D) the recombination frequency between two independently assorting genes

Question 34

Use the following map of four genes on a chromosome to answer the question. When collecting data from genetic crosses which gene pair is most likely to show the highest frequency of recombination?

A) A and W
B) E and G
C) A and E
D) A and G

Question 35

Use the following information to answer the question.
A plantlike organism on the hypothetical planet Pandora has three genetic traits: leaf color, controlled by gene L; a stem texture, controlled by gene S; and root length controlled by gene R. The three genes are linked and recombine.
A geneticist performed a testcross with a strain of the organism that is heterozygous for the three traits. She recorded progeny with the following phenotypic distribution:

What is the approximate distance between genes L and S?

A) 3 map units
B) 6 map units
C) 15 map units
D) 30 map units

Question 36

Which of the following events will result in recombination between linked genes?

A) Nonhomologous chromosomes breaking and then rejoining with one another.
B) Incomplete independent assortment.
C) Linked genes traveling together at anaphase.
D) Crossovers between genes resulting in chromosomal exchange.

Question 37

Recombination between linked genes is an adaptive advantage within a changing environment because ________.

A) recombination allows genes to be shuffled along chromosomes
B) recombination must occur or genes will not assort independently
C) new allele combinations increase diversity in a population
D) recombination ensures each offspring will have an increased chance of survival

Question 38

If cell Q enters meiosis, and nondisjunction of one chromosome occurs in one of its daughter cells during meiosis II, how will this affect the gametes at the completion of meiosis?

A) All the gametes descended from cell Q will be diploid.
B) Half of the gametes descended from cell Q will be n + 1, and half will be n - 1.
C) One-quarter of the gametes descended from cell Q will be n + 1, one-quarter will be n - 1, and half will be n.
D) Two of the four gametes descended from cell Q will be haploid, and two will be diploid.

Question 39

What is the greatest benefit of using a testcross to determine an unknown genotype?

A) The homozygous recessive parent is obvious to the naked eye.
B) The homozygous parent is the only one whose crossovers make a difference.
C) A progeny's phenotype reflects the contribution from the heterozygous parent.
D) All of the progeny will be heterozygous.

Question 40

Use the following information to answer the question. In a series of mapping experiments, the recombination frequencies for four different linked genes of Drosophila were determined as shown in the figure. Based on this information, what is the order of these genes on a chromosome map?

A) rb-cn-vg-b
B) cn-rb-b-vg
C) b-rb-cn-vg
D) vg-cn-b-rb

Question 41

Which of the following statements is generally true of aneuploidies in newborns?

A) A monosomy is more frequent than a trisomy.
B) Monosomy X is the only viable monosomy known to occur in humans.
C) Human aneuploidy usually conveys an adaptive advantage in humans.
D) An aneuploidy resulting in the deletion of a chromosome segment is less serious than duplication.

Question 42

Some snail species' shells can have right-handed direction of shell coiling or left-handed direction of shell coiling. The direction of coiling depends on a protein deposited by the mother in the egg cytoplasm with DD and Dd mothers depositing a protein that directs right-handed direction of coiling in shells. If Dd egg-producing snail and a dd sperm-producing snail mate what genotype(s) and phenotype(s) of offspring will result?

A) 1/2 Dd:1/2 dd; all right-coiling
B) all Dd; all right-coiling
C) 1/2 Dd: 1/2 dd; half right-coiling and half left-coiling
D) all Dd; half right-coiling and half left-coiling

Question 43

Use the following figure to answer the question. Shaded symbols indicate affected individuals. The pedigree in the figure shows the transmission of a trait in a particular family. Based on this pattern of transmission, the trait is most likely ________.

A) mitochondrial
B) sex-linked dominant
C) sex-linked recessive
D) autosomal dominant

Question 44

A patient has 47 chromosomes, including three X chromosomes. Which of the following statements describes her expected phenotype?

A) a female with masculine characteristics such as facial hair
B) an apparent male who is sterile
C) healthy female of slightly above-average height
D) a sterile female

Question 45

If a pair of homologous chromosomes fails to separate during meiosis I, select the choice that shows the chromosome number of the four resulting gametes with respect to the normal haploid number (n)?

A) n + 1; n + 1; n - 1; n - 1
B) n + 1; n - 1; n; n
C) n + 1; n - 1; n - 1; n - 1
D) n + 1; n + 1; n; n

Question 46

Which of the following statements correctly describes what happens to a chromosome after a nonreciprocal translocation?

A) a Philadelphia chromosome is generated
B) a duplication of part of the chromosome occurs
C) nondisjunction of pairs of homologous occurs
D) a chromosome transfers a fragment but receives none in return

Question 47

German scientist Carl Correns found that the inheritance of variegated color on the leaves of certain plants was determined only by the maternal parent. Which of the following phenomena best explains this pattern of inheritance?

A) nondisjunction
B) inheritance of plastid genes
C) genomic imprinting
D) sex linkage

Question 48

Genomic imprinting is generally due to the addition of methyl (-CH3) groups to cytosine nucleotides to silence a given allele of a gene. If this process depends on the sex of the parent who transmits the gene, which of the following statements must be true?

A) Genes required for early development stages must not be imprinted.
B) Methylation of this kind must occur more in males than in females.
C) Methylation must be reversible in ovarian and testicular cells.
D) The imprints are transmitted only to gamete-producing cells.

Question 49

Which of the following statements describes the most likely result of a defect in meiosis that results in the failure of spindle microtubules to bind some kinetochores?

A) New microtubules with more effective binding capabilities to kinetochores will be synthesized to compensate for the defect.
B) Excessive cell divisions will occur resulting an increase in the chromosome number known as polyploidy.
C) The defect will be bypassed in order to ensure normal chromosome distribution in the new cells.
D) The resulting cells will not receive the correct number of chromosomes in the gametes, a condition known as aneuploidy.

Question 50

A couple has a child with Down syndrome. Which of the following is the most probable cause of the child's condition?

A) The man's family has a predisposition for Down syndrome.
B) The woman's genome has a chromosomal duplication.
C) One member of the couple underwent nondisjunction in somatic cell production.
D) One member of the couple underwent nondisjunction during meiosis.

Question 51

Which of the following is an example of monosomy in humans?

A) Turner syndrome
B) Klinefelter syndrome
C) Down syndrome
D) trisomy X

Question 52

A phenotypically normal couple seeks genetic counseling because the man's karyotype showed that his chromosomes had a reciprocal translocation between chromosomes 4 and 12. Because the translocation is reciprocal there was no genetic information lost and he is healthy; however, he and his wife want to know the probability that his sperm cells will be abnormal. Which fraction of his sperm cells is predicted to carry at least one chromosome with a translocation?

A) three-fourth will have at least one chromosome with a translocation; the other 1/4 will carry normal chromosomes 4 and 12
B) all will carry the same translocation as the father
C) none will carry the translocation
D) one-half will have the father's translocation and 1/2 will carry normal chromosomes 4 and 12

Question 53

Abnormal chromosomes are frequently found in malignant tumors. Errors such as translocations may place a gene in close proximity to different control regions that could result in which of the following events?

A) an increase in nondisjunction
B) expression of genes that lead to inappropriate cell division
C) a decrease in mitotic frequency
D) failure of the cancer cells to multiply

Question 54

Which of the following correctly describes a Philadelphia chromosome?

A) a human chromosome 22 that has had a specific translocation from chromosome 9
B) a human chromosome 9 that is found only many types of cancer
C) a chromosome found only in mitochondria
D) a chromosome with a point mutation that increases cell division