GENETICS QUIZ #4

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?

A mutation has occurred in the SRY gene making it inactive.

Question 12 In humans, occasionally a baby is found that has the XX chromosomal karyotype but is phenotypically male. Which of the following statements might be a CORRECT explanation for at least some of these unusual cases?

A piece of chromosomal material containing an active SRY gene is found attached to one of the X chromosomes.

What is the apparent purpose for X inactivation in humans and other mammals?

It allows for the levels of expression of genes on the X chromosome to be similar in males and females.

What is the role of the SRY gene in humans?

It is located on the Y chromosome and initiates the developmental pathway toward the male phenotype.

What is the expected outcome for a human embryo with the XXXY chromosome constitution?

It would likely develop into a sterile male with reduced testes.

Question 19 Women with Turner syndrome (XO) and normal women (XX) are clearly different phenotypically. In addition, the vast majority of XO conceptions abort before birth. However, both XO and XX women have one active X chromosome since the X in XO women remains active and one might expect that they would therefore have similar phenotypes. What is the MOST reasonable explanation for their different phenotypes?

Some genes remain active on the inactive X chromosome and XX women will have two copies of these genes expressed and XO women only one copy.

Species in which individuals have only male or only female reproductive structures are called:

dioecious.

In a germ-line cell from a female grasshopper (XX-XO sex determination system), when do the homologous X chromosomes segregate?

during meiosis I, anaphase

In a germ-line cell from a human male that is dividing, when do the X and Y chromosomes segregate?

during meiosis I, anaphase

In Drosophila, flies that are XXY but have a normal diploid set of autosomes have been found. Such XXY chromosome constitutions have also been found in humans. The sex of such individuals is expected to be:

female in Drosophila but male in humans.

Human males with XY chromosomes are _____ and produce two different kinds of gametes, whereas females with XX chromosomes are _____ and produce only one kind.

heterogametic; homogametic

With the XX-XO sex determination system, generally:

male offspring have one X chromosome, and it is inherited from their mother.

An XXY chromosome constitution produces _____ development in humans and _____ development in fruit flies.

male; female

During the evolution of the human Y chromosome, all of the following are assumed to occur EXCEPT:

many of the genes on the early X chromosome that were responsible for critical cellular functions got moved to the evolving Y chromosome.

In which of the following organisms is gender/sex determined by the temperature during embryonic development?

many turtles and alligators

Species in which an individual organism has both male and female reproductive structures are called:

monoecious

The sex determination system used by Drosophila is called:

the X:A sex determination system.

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?

Some of the boys are XXY

In species of birds, males are the homogametic sex and females the heterogametic sex. Which of the following statements is TRUE in this system of sex determination?

The gender of the offspring is determined by the female parent.

What is the sex chromosome constitution of a male duck-billed platypus?

XXXXXYYYYY

Which of the following human genotypes is associated with Klinefelter syndrome?

XXY

In which of the following phenotypic females do testes develop?

XY with the X-linked recessive condition of androgen-insensitivity syndrome

Which of the following chromosome constitutions would never lead to a viable human baby being born?

YY

Human females with XY chromosomes and a phenotype that includes the absence of a uterus and ovaries and the presence of testes are likely to have which of the following mutations?

a mutation in the androgen receptor gene

A female with androgen-insensitivity syndrome, a sex-linked recessive condition, has:

a pair of testes that produce testosterone.