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Exam 15: The Chromosomal Basis of Inheritance

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Question 1

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What is an adaptive advantage of recombination between linked genes?

A) Recombination is required for independent assortment.
B) Recombination must occur or genes will not assort independently.
C) New allele combinations are acted upon by natural selection.
D) The forces on the cell during meiosis II result in recombination.

E) A) and D)
F) A) and C)

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Question 2

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Use the following information to answer the question. The numbers in the boxes are the recombination frequencies in between the genes (in percent) . 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

E) A) and B)
F) None of the above

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Question 3

Multiple Choice

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If cell X 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?

Red-green color blindness is a sex-linked recessive trait in humans. Two people with normal color vision have a color-blind son. What are the genotypes of the parents?

A woman is found to have 47 chromosomes, including three X chromosomes. Which of the following statements describes her expected phenotype?

Abnormal chromosomes are frequently found in malignant tumors. Errors such as translocations may place a gene in close proximity to different control regions. Which of the following events might then occur to make the cancer worse?

In birds, sex is determined by a ZW chromosome scheme. Males are ZZ and females are ZW. A recessive lethal allele that causes death of the embryo is sometimes present on the Z chromosome in pigeons. What would be the sex ratio in the offspring of a cross between a male that is heterozygous for the lethal allele and a normal female?

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

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 all had red fruit and yellow flowers. The F₁ were testcrossed by 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?

Duchenne muscular dystrophy is a serious condition caused by a recessive allele of a gene on the human X chromosome. The patients have muscles that weaken over time because they have absent or decreased dystrophin, a muscle protein. They rarely live past their 20s. How likely is it for a woman to have this condition?

Which of the following occurrences describes how recombination between linked genes comes about?

Map units on a linkage map cannot be relied upon to calculate physical distances on a chromosome for which of the following reasons?

In cats, black fur color is determined by an X-linked allele; the other allele at this locus determines orange color. The heterozygote is tortoiseshell. What kinds of offspring would you expect from the cross of a black female and an orange male?

Generally, only female cats have the tortoiseshell phenotype for fur color. Which of the following statements explains this phenomenon?

Which of the following statements correctly describes the meaning of the chromosome theory of inheritance as expressed in the early 20th century?

One possible result of chromosomal breakage is for a fragment to join a nonhomologous chromosome. What is this type of chromosomal alteration called?

In humans, clear gender differentiation occurs not at fertilization, but after the second month of gestation. Which of the following statements describes the first event of this differentiation?

A man who is a dwarf with achondroplasia and normal vision marries a color-blind woman of normal height. The man's father was six feet tall, and both the woman's parents were of average height. Dwarfism caused by achondroplasia is autosomal dominant, and red-green color blindness is X-linked recessive. How many of their daughters might be expected to be color-blind with achondroplasia?

Which of the following statements regarding gene linkage is correct?

Use the following map of four genes on a chromosome to answer the question. Between which two genes would you expect the highest frequency of recombination?