Exam 15: The Chromosomal Basis of Inheritance

Suppose that a gene on human chromosome 18 can be imprinted in a given pattern in a female parent but not in a male parent. A couple in whom each maternal meiosis is followed by imprinting of this gene have children. What can we expect as a likely outcome?

SRY is best described in which of the following ways?

Use the following information to answer the questions below. The following is a map of four genes on a chromosome. -Between which two genes would you expect the highest frequency of recombination?

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?

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

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? I. an error in anaphase I II. an error in anaphase II III. an error of the first postfertilization mitosis IV. an error in pairing

A certain kind of snail can have a right-handed direction of shell coiling (D)or left-handed coiling (d). If direction of coiling is due to a protein deposited by the mother in the egg cytoplasm, then a Dd egg-producing snail and a dd sperm-producing snail will have offspring of which genotype(s)and phenotype(s)?

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

A phenotypically normal prospective couple seeks genetic counselling 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?

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

Recombination between linked genes comes about for what reason?

Refer to the following information to answer the questions below. A man who is an achondroplastic dwarf with normal vision marries a colour-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 colour blindness is X-linked recessive. -What proportion of their sons would be colour-blind and of normal height?

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

In humans, male-pattern baldness is controlled by an autosomal gene that occurs in two allelic forms. Allele Hn determines nonbaldness, and allele Hb determines pattern baldness. In males, because of the presence of testosterone, allele Hb is dominant over Hn. If a man and woman both with genotype HnHb have a son, what is the chance that he will eventually be bald?

Down syndrome has a frequency in the U.S. population of ~1/700 live births. In which of the following groups would you expect this frequency to be significantly higher?

What is the greatest benefit of having used a testcross for this experiment?

Women (and all female mammals)have one active X chromosome per cell instead of two. What causes this?

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

Use the following information to answer the questions below. A plant-like organism on the planet Pandora has 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, when a geneticist did a testcross with an organism that had been found to be heterozygous for the three recessive traits, she was able to identify progeny with the following phenotypic distribution (+ = wild type): -Which of the following are the phenotypes of the parents in this cross?

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