Chapter 6. 6·14–6·16 There are sex differences in the chromosomes.

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Instructions

Check your understanding of concepts from 6·14–6·16 There are sex differences in the chromosomes by answering the following questions.

1.

1. Which of the following is TRUE about sex determination in humans?

An X chromosome is smaller than a Y chromosome.

Without a Y chromosome, a fertilized egg usually dies.

One would expect babies to have two Y chromosomes about half the time.

In the absence of a Y chromosome, the fetal gonads develop into testes, not ovaries.

The father's sperm determines the gender of a baby.

Correct! (See section 6·14 How is sex determined in humans?)

Incorrect. (See section 6·14 How is sex determined in humans?)

2.

2. In some species, sex is determined by environmental, rather than genetic, factors. This is true of:

kangaroos.

bees.

turtles.

humans.

birds.

Correct! (See section 6·16 This is how we do it: Can the environment determine the sex of a turtle’s offspring?)

Incorrect. (See section 6·16 This is how we do it: Can the environment determine the sex of a turtle’s offspring?)

3.

3. Which of the following is NOT a method of sex determination that occurs in nature?

All of the above are naturally occurring examples of sex determination.

In bees, the eggs that the queen allows to be fertilized become females and the eggs she doesn't fertilize become males.

In birds, the female is the heterogametic (ZW) sex and the male is the homogametic (ZZ) sex.

In sea turtles, eggs laid in hot sand becomes females and eggs laid in cooler sand become males.

In humans, the male is the heterogametic (XY) sex and the female is the homogametic (XX) sex.

Correct! (See section 6·15 the sex of offspring is determined in a variety of ways in non-human species.)

Incorrect. (See section 6·15 the sex of offspring is determined in a variety of ways in non-human species.)

4.

4. Of all the varying types of sex-chromosomal abnormalities, one possibility—that of an individual having one Y but no X—has never been reported. Which of the following statements is the most likely reason that medical researchers have yet to report a person having the karyotype of one Y but no X?

Our current technology for karyotyping would not reveal such an abnormality.

People are probably born with this karyotype; however, since the phenotypic abnormalities caused by it are so slight, the individuals live out their lives normally and are unaware of it.

The X chromosome contains genes that are unrelated to sex determination and are necessary for life.

The Y chromosome needs the X chromosome to be present in the cell in order for its genes to be expressed.

There does not exist a meiotic event that could produce an oocyte that does not have a X chromosome.

Correct! (See section 6·14 How is sex determined in humans?)

Incorrect. (See section 6·14 How is sex determined in humans?)

5.

5. Which of the following statements is NOT correct of human sex chromosomes?

All diploid cells have both an X and a Y chromosome.

On average, half a man's sperm carry an X chromosome and half carry a Y.

X and Y chromosomes differ in structure.

All diploid cells have at least one X chromosome.

Gametes produced by females have an X chromosome, but not a Y.

Correct! (See section 6·15 the sex of offspring is determined in a variety of ways in non-human species.)

Incorrect. (See section 6·15 the sex of offspring is determined in a variety of ways in non-human species.)

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