* not completed

. The germplasm in Drosophila is specified by

bicoid correct incorrect

Hox genes correct incorrect

oskar correct incorrect

the point of sperm entry correct incorrect

* not completed

. 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?

All mark the posterior end of the antero-posterior axis. correct incorrect

All are present at fertilization in the vegetal pole of the egg. correct incorrect

All are determinants that specify the dorso-ventral axis of the fertilized egg. correct incorrect

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

* not completed

. In mice, germ cells can be first identified

in prospective mesoderm of the proximal epiblast, as Blimp1-expressing cells correct incorrect

in the mesoderm that will form gonadal tissue correct incorrect

in the posterior tip of the embryo, as cells containing pole plasm correct incorrect

in the genital ridge, as Oct4-expressing cells correct incorrect

* not completed

. Which feature of meiosis, as compared with mitosis, is most important for the production of gametes?

Homologous chromosomes separate in meiosis I, whereas sister chromatids separate in mitosis. correct incorrect

Meiosis leads to the production of haploid products, whereas mitosis leads to diploid daughter cells. correct incorrect

Meiosis provides an opportunity for recombination, whereas mitosis does not. correct incorrect

Typically, three of the four products do not become oocytes during meiosis in female organisms, whereas mitosis will produce four functional products after two rounds of cell division. correct incorrect

* not completed

. In what stage of which type of cell division is the oocyte at the birth of a female mammal?

The oocyte is in G₁ of the mitotic cell cycle. correct incorrect

The oocyte is in metaphase of meiosis II. correct incorrect

The oocyte is in prophase of meiosis I. correct incorrect

The oocyte is in prophase of mitosis. correct incorrect

* not completed

. The human congenital disorder Angelman syndrome is due to the inheritance of a maternal chromosome 15 that has a small deletion of a specific region. Why does this deletion not behave as a recessive allele; that is, why is its loss not made up for by the intact region on the unmutated paternal chromosome 15?

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. correct incorrect

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. correct incorrect

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. correct incorrect

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

* not completed

. What is the acrosomal reaction?

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

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

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

The acrosomal reaction is the entry of the sperm nucleus into the egg. correct incorrect

* not completed

. What is the zona pellucida of the mammalian egg?

A hardened membrane that forms a physical block to polyspermy, formed from the vitelline membrane and the contents of the cortical granules correct incorrect

A layer of follicle-derived cells called cumulus cells correct incorrect

An extracellular layer of glycoproteins correct incorrect

The plasma membrane of the egg correct incorrect

* not completed

. What is the cortical reaction in sea urchin eggs, and why is it important?

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

The cortical reaction is the entry of Ca²⁺ ions into the egg via the cortex, which initiates development. correct incorrect

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

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. correct incorrect

* not completed

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

a male. correct incorrect

a female. correct incorrect

an hermaphrodite. correct incorrect

an individual with no secondary sexual characteristics. correct incorrect

* not completed

. Secretion of Müllerian-inhibiting substance by Sertoli cells

causes the Müllerian ducts to develop into the oviducts correct incorrect

causes the Müllerian ducts to develop into Wolffian ducts correct incorrect

causes the testis to produce testosterone correct incorrect

causes the Müllerian ducts to regress by apoptosis in males correct incorrect

* not completed

. The mammalian oviduct will form from the

mesonephros correct incorrect

Müllerian duct correct incorrect

ureter correct incorrect

Wolffian duct correct incorrect

* not completed

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

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. correct incorrect

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

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. correct incorrect

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

* not completed

. The molecular activity of the Sex-lethal protein of Drosophila is

as a 'numerator', counting the number of X chromosomes correct incorrect

as a transcription factor correct incorrect

to control RNA splicing correct incorrect

to signal to the Tra receptor correct incorrect

* not completed

. The C. elegans GLP-1 protein involved in germ cell differentiation is similar to which mammalian signaling protein?

BMPs correct incorrect

Delta correct incorrect

Notch correct incorrect

testosterone receptor correct incorrect

* not completed

. In mammals, dosage compensation is carried out by

decreasing the transcription of the X in males correct incorrect

increasing the transcription of the X in males correct incorrect

inactivating one X chromosome in females by condensation as heterochromatin correct incorrect

degrading one X chromosome in all female cells early in development correct incorrect