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Exam 15: The Chromosomal Basis of Inheritance

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Question 31

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Pseudohypertrophic muscular dystrophy is an inherited disorder that causes gradual deterioration of the muscles. It is seen almost exclusively in boys born to apparently normal parents and usually results in death in the early teens. Is this disorder caused by a dominant or a recessive allele? Is its inheritance sex-linked or autosomal? How do you know? Explain why this disorder is almost never seen in girls.

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Recessive; if the disorder were dominant...

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Question 32

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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?

A) 1/4 will be normal, 1/4 with the translocation, 1/2 with duplications and deletions.
B) All will carry the same translocation as the father.
C) None will carry the translocation since abnormal sperm will die.
D) His sperm will be sterile and the couple might consider adoption.
E) 1/2 will be normal and the rest with the father's translocation.

F) All of the above
G) B) and C)

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Question 33

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A nonreciprocal crossover causes which of the following products?

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

Refer to Figure 15.2 to answer the following questions. $\text {The numbers in the boxes are the recombination}$ $\text {frequencies in between the genes (in percent) .}$ Figure 15.2 -In a series of mapping experiments, the recombination frequencies for four different linked genes of Drosophila were determined as shown in the figure. What is the order of these genes on a chromosome map?

A wild-type fruit fly (heterozygous for gray body color and normal wings)is mated with a black fly with vestigial wings. The offspring have the following phenotypic distribution: wild type, 778; black-vestigial, 785; black-normal, 158; gray-vestigial, 162. What is the recombination frequency between these genes for body color and wing size?

If nondisjunction occurs in meiosis II during gametogenesis, what will be the result at the completion of meiosis?

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

Mitochondrial DNA is primarily involved in coding for proteins needed for electron transport. Therefore in which body systems would you expect most mitochondrial gene mutations to be exhibited?

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

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?

In order for chromosomes to undergo inversion or translocation, which of the following is required?

Abnormal chromosomes are frequent 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?

Refer to Figure 15.2 to answer the following questions. $\text {The numbers in the boxes are the recombination}$ $\text {frequencies in between the genes (in percent) .}$ Figure 15.2 -Which of the following two genes are closest on a genetic map of Drosophila?

Women born with an extra X chromosome (XXX)are healthy and phenotypically indistinguishable from normal XX women. What is a likely explanation for this finding? How could you test this explanation?

Women with Turner syndrome have a genotype characterized as which of the following?

A Barr body is normally found in the nucleus of which kind of human cell?

Males are more often affected by sex-linked traits than females because

A cell that has 2n + 1 chromosomes is

If a pair of homologous chromosomes fails to separate during anaphase of meiosis I, what will be the chromosome number of the four resulting gametes with respect to the normal haploid number (n) ?