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Question 1

What generalization can be applied to the pole plasm of Drosophila, the P-granules of C. elegans, the yolk-free vegetal cytoplasm of Xenopus, and the localized mRNA for vasa in zebrafish?

a) All mark the posterior end of the antero-posterior axis.

b) All are present at fertilization in the vegetal pole of the egg.

c) All are determinants that specify the dorso-ventral axis of the fertilized egg.

d) All mark the special region of cytoplasm, the germplasm, that is involved in specification of germ cells.

e) All are different names for the cells that become the germ cells of the adult animal.

Question 2

Why is meiosis required for germ cell formation, yet is never used by somatic cells?

a) Meiosis is the cell division process that produces haploid products.

b) Meiosis is a process that produces one sperm and one egg from each dividing germ cell.

c) Meiosis is a specialized, highly efficient process of cell division, which is used because of the large numbers of germ cells required by an organism.

d) Meiosis is a specialized form of cell division that produces four diploid cells instead of just two, facilitating the production of large numbers of germ cells.

e) Meiosis is never used by somatic cells because the two rounds of division involved would take too long for use by somatic cells.

Question 3

Two human disorders, Prader-Willi syndrome and Angelman syndrome, occur when the mother contributes a copy of chromosome 15 that contains a small deletion in a specific region. Why does this small deletion not behave as a recessive allele, that is, why is its loss not made up for by the good copy of the region on the paternally contributed chromosome 15?

a) This portion of chromosome 15 is invariably mutated in males, so the father, too, contributes recessive alleles that are thus homozygous and perturb development.

b) The father's copy of chromosome 15 has genes in the region of the deletion that are imprinted, and thus inactive; in the absence of any active copies of these genes, development cannot proceed normally.

c) The genes in this portion of chromosome 15 are special in that they are required in two copies for normal development, and so the loss of one set does not allow normal development.

d) Two copies of every gene in the genome are required for development, so loss of one of the copies from this region perturbs development.

e) Chromosomes with deletions do not go through mitosis correctly, so cell divisions in the embryo result in cells with abnormal numbers of chromosomes, and these cells do not contribute properly to the development of the organism.

Question 4

What is the 'acrosomal reaction'?

a) The acrosomal reaction is a repulsive interaction between the sperm and the egg.

b) The acrosomal reaction is the digestion of the acrosome by the sperm when it encounters an egg.

c) The acrosomal reaction is the digestion of the zona pellucida, permitting the sperm to contact the egg.

d) The acrosomal reaction is the fusion of the sperm and egg plasma membranes.

e) The acrosomal reaction is the entry of eh sperm nucleus into the egg.

Question 5

What is the cortical reaction, and why is it important?

a) The cortical reaction is the fusion of the egg cortex with the egg plasma membrane, which allows the sperm to enter.

b) The cortical reaction is the entry of Ca²⁺ ions into the egg, which initiates development.

c) The cortical reaction is the exocytosis of the cortical granules during egg maturation, which contain the components of the zona pellucida.

d) The cortical reaction is the depolarization of the plasma membrane after sperm entry, which helps to block polyspermy.

e) The cortical reaction is the release of the cortical granules after sperm entry, which converts the vitelline membrane into the fertilization membrane which blocks polyspermy.

Question 6

In humans, an individual with an XXY chromosomal complement will develop as:

a) a male.

b) a female.

c) an hermaphrodite.

d) a super-female.

e) an individual with no secondary sexual characteristics.

Question 7

Secretion of Müllerian-inhibiting substance by Sertoli cells:

a) causes the Müllerian ducts to develop into the oviducts.

b) causes the Müllerian ducts to develop into Wolffian ducts.

c) causes the Wolffian duct to develop into the vas deferens.

d) causes the testis to produce testosterone.

e) causes the Müllerian duct to regress by apoptosis in males.

Question 8

In what way, if any, does the chromosomal determination of sex differ in Drosophila and humans?

a) In humans, the Y chromosome determines maleness, with female development being a default state, but in Drosophila, the presence of two X chromosomes determines femaleness, and male development is the default state.

b) In humans, the Y chromosome determines maleness, but in Drosophila, the ratio of X chromosomes to autosomes determines maleness or femaleness.

c) In humans, it is the presence of only one X chromosome that triggers male development, and two X chromosomes trigger female development, just as occurs in Drosophila.

d) In human males, a single Y chromosome is present in the absence of an X chromosome, while in Drosophila, a single X chromosome is present in the absence of a Y chromosome.

e) There is no fundamental difference: in both organisms, the Y chromosome determines maleness.

Question 9

What is the molecular activity of the Sex-lethal protein of Drosophila?

a) Sex-lethal is a transcription factor that activates female-specific genes.

b) Sex-lethal is a repressor of the transcription of male-specific genes.

c) Sex-lethal controls the splicing of specific mRNAs such that certain proteins required for female development are produced only in females.

d) Sex-lethal protein is equivalent to testosterone in mammals, in determining male development.

e) Sex-lethal protein is equivalent to estrogen in mammals, in determining female development.

Question 10

In mammals, dosage compensation is carried out by:

a) decreasing the transcription of the X in males.

b) increasing the transcription of the X in males.

c) inactivating one X chromosome in females by condensation as heterochromatin.

d) inactivating one X chromosome in males by condensation as heterochromatin.

e) degrading one X chromosome in all female cells early in development.

Oxford University Press, Online Resource Centre, Chapter 11.

Chapter 11

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