Question 1

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?

Accepted Answer

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

Question 2

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?

Accepted Answer

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 3

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?

Accepted Answer

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 4

Which of the following statements regarding gene linkage is correct?

Accepted Answer

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 5

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

Accepted Answer

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 6

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?

Accepted Answer

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

Question 7

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

Accepted Answer

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 8

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?

Accepted Answer

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 9

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?

Accepted Answer

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 10

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?

Accepted Answer

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

Question 11

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?

Accepted Answer

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 12

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?

Accepted Answer

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 13

Which of the following correctly describes a Philadelphia chromosome?

Accepted Answer

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

Question 14

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

Accepted Answer

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 15

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

Accepted Answer

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

Question 16

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

Accepted Answer

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 17

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?

Accepted Answer

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

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 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.

Accepted Answer

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

Question 19

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?

Accepted Answer

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 20

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?

Accepted Answer

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.

Exam 15: Linkage and Chromosomes