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Exam 12: The Chromosomal Basis of Inheritance

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Question 1

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At what point in cell division is a chromosome lost so that, after fertilization with a normal gamete, the result is an embryo with 45,X?

A) after an error occurring in anaphase I or anaphase II
B) after an error occurring in anaphase I only
C) after an error occurring in anaphase II only
D) after an error occurring in prophase I only
E) after an error occurring in metaphase II only

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Question 2

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Cinnabar eyes is a sex-linked recessive characteristic in fruit flies. If a female having cinnabar eyes is crossed with a wild-type male, what percentage of the F1 males will have cinnabar eyes?

A) 0%
B) 25%
C) 50%
D) 75%
E) 100%

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Question 3

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

Why does recombination between linked genes continue to occur?

Sex determination in mammals is due to the SRY gene on the Y chromosome. An abnormality of this region could allow which of the following to have a male phenotype?

How would one explain a testcross involving F1 dihybrid flies in which more parental-type offspring than recombinant-type offspring are produced?

Which of the following statements correctly describes aneuploid conditions?

A woman is found to have 47 chromosomes, including three X chromosomes. Which of the following 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 might then occur to make the cancer worse?

Sturtevant provided genetic evidence for the existence of four pairs of chromosomes in Drosophila in which of the following ways?

Please use the following information to answer the question(s) below. A man who is an achondroplastic dwarf with normal vision marries a color-blind woman of normal height. The man's father was 6 feet tall, and both the woman's parents were of average height. Achondroplastic dwarfism is autosomal dominant, and red-green color blindness is X-linked recessive. -What proportion of their sons would be color-blind and of normal height?

Of the following human aneuploidies, which is the one that generally has the most severe impact on the health of the individual?

Figure 12.2 In a series of mapping experiments, the recombination frequencies for four different linked genes of Drosophila were determined as shown in Figure 12.2. What is the order of these genes on a chromosome map?

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?

Which of the following statements best describes the SRY gene?

Please use the following information to answer the question(s) below. A man who is an achondroplastic dwarf with normal vision marries a color-blind woman of normal height. The man's father was 6 feet tall, and both the woman's parents were of average height. Achondroplastic dwarfism is autosomal dominant, and red-green color blindness is X-linked recessive. -How many of the couple's daughters might be expected to be color-blind dwarfs?

Which of the following events causes recombination between linked genes to occur?

A phenotypically normal prospective couple seeks genetic counseling because the man knows that he has a translocation of a portion of his chromosome 4 that has been exchanged with a portion of his chromosome 12. Although he is normal because his translocation is balanced, he and his wife want to know the probability that his sperm will be abnormal. What is your prognosis regarding his sperm?

Please use the following information to answer the question(s) below. A plantlike organism on the planet Pandora can have three recessive genetic traits: bluish leaves, due to an allele (a) of gene A; a feathered stem, due to an allele (b) of gene B; and hollow roots due to an allele (c) of gene C. The three genes are linked and recombine. A geneticist did a testcross with an organism that had been found to be heterozygous for the three recessive traits and was able to identify progeny of the phenotypic distribution (+ = wild type) shown in Figure 12.3. Figure 12.3 -If recombination frequency is equal to distance in map units, what is the approximate distance between genes A and B?

One map unit is equivalent to which of the following values?