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Exam 4: Sex Determination and Sex-Linked Characteristics

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Question 41

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A man and a woman are trying to have children but are unsuccessful. The man's autosomes appear normal, but his sex chromosomes, shown in the following diagram, are not. The diagram also shows a normal male's sex chromosomes for reference. Can you tell if the mutation came from the man's mother or the man's father? Explain how you can tell.

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Question 42

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Familial vitamin-D-resistant rickets is an X-linked dominant condition in humans. If a man is afflicted with this condition and his wife is normal, it is expected that among their children, all the daughters would be affected and all the sons would be normal. In families where the husband is affected and the wife is normal, this is almost always the outcome among their children when such families have been studied. Very rarely an unexpected result occurs in such families where a boy is born with the disorder. If the chromosomes of such unusual boys are examined, what might be expected to be found?

A) Some of the boys are XYY.
B) Some of the boys are XY but have lost the SRY gene from their Y chromosome.
C) Some of the boys are YY.
D) Some of the boys are XXY.
E) Some of the boys are XXX.

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Question 43

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Which of the following statements about X inactivation in mammalian females is FALSE?

List three dosage compensation strategies for equalizing the amount of sex chromosome gene products.

Which of the following statements about the sex-linked recessive trait of red-green color blindness in humans is FALSE?

Suppose that an apparently female athlete fails a gender test and is not allowed to compete in her event. The gender test is based on examination of cheek cells for the presence of one or more Barr bodies. Later, it is discovered that the athlete has androgen-insensitivity syndrome. What is the chromosome constitution of a person with androgen-insensitivity syndrome?

Red-green color blindness is X-linked recessive. A woman with normal color vision has a father who is color blind. The woman has a child with a man with normal color vision. Which phenotype is NOT expected?

In which of the following phenotypic females do testes develop?

List three different mechanisms for generating sexes in dioecious species.

You discover a new mutation in Drosophila that causes an abnormal wing shape. When a male fly with this mutation is crossed to a homozygous normal female, the F₁ are all wild-type phenotypically. The F₂ flies consist of ¹/₂ phenotypically normal females, ¹/₄ phenotypically normal males, and ¹/₄ males with abnormal wings. What is the MOST likely explanation for the new mutant allele?

In humans there is a genetic disorder that results from a dominant mutation present in a gene located in the pseudoautosomal region of the Y chromosome and on the X chromosome. Which of the following statements is CORRECT?

A woman has normal vision although her maternal grandfather (her mother's father) had red-green color blindness, a sex-linked recessive trait. Her maternal grandmother and the woman's own father are assumed to not possess a copy of the mutant allele. The woman marries a man with normal vision although his father was color blind. What is the probability that the first child of this couple will be color blind?

Explain the genders of human and diploid Drosophila XO individuals.

A eukaryotic diploid cell from an organism with the XX-XO sex determination system has two pairs of autosomes and one X chromosome, shown here. A diploid cell from this individual begins to go through meiosis. After the completion of meiosis I, it becomes two cells. One of these two cells now undergoes meiosis II. Which of the following is a possible normal combination of chromosomes in one of the subsequent two cells after the completion of meiosis II?

Miniature wings in Drosophila are due to an X-linked allele (X^m) that is recessive to the wild-type allele for normal long wings (X⁺) . Sepia eyes are produced by an autosomal allele (se) , which is recessive to the wild-type allele for red eyes (se⁺) . A female that is homozygous for normal wings and has sepia eyes is crossed with a male that has miniature wings and is homozygous for red eyes. The F₁ offspring are intercrossed to produce the F₂ generation. What proportion of the F₂ females is expected to have miniature wings and sepia eyes?

Explain the development of female external anatomy in individuals with androgen-insensitivity syndrome.

If a male bird that is heterozygous for a recessive Z-linked mutation is crossed to a wild-type female, what proportion of the progeny will be mutant males?

In humans, occasionally a baby is found that has the XY chromosomal karyotype but is phenotypically female. Which of the following statements might be a CORRECT explanation for at least some of these unusual cases?

While doing summer fieldwork on a remote Indonesian island, you discover a new genus of lizard closely related to Komodo dragons. You attempt to discover what sex determination system it uses by performing a series of controlled crosses on the island, using an isolated pair of lizards. Initially, all your crosses yield only males (in significant numbers). As fall begins and you prepare to leave the island, you find that your last cross yielded only females (in significant numbers). Suggest a mode of sex determination that explains these data.

James is a 42-year-old man with hemophilia, a sex-linked recessive condition. His daughter, Susan, who has normal blood clotting, is married to Fred who also has hemophilia. Susan and Fred are expecting their first child and an ultrasound shows that the fetus is male. What is the approximate probability that their new son will have hemophilia?