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Return to Principles of Development 6e Student Resources
Chapter 9 Self-test questions
Germ cells, fertilization, and sex
The germplasm in
is specified by
the point of sperm entry
What generalization can be applied to the pole plasm of
, the P-granules of
, the yolk-free vegetal cytoplasm of
, and the localized mRNA for
All mark the posterior end of the antero-posterior axis.
All are present at fertilization in the vegetal pole of the egg.
All are determinants that specify the dorso-ventral axis of the fertilized egg.
All mark the special region of cytoplasm, the germplasm, that is involved in specification of germ cells.
In mice, germ cells can be first identified
in prospective mesoderm of the proximal epiblast, as
in the mesoderm that will form gonadal tissue
in the posterior tip of the embryo, as cells containing pole plasm
in the genital ridge, as
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.
Meiosis leads to the production of haploid products, whereas mitosis leads to diploid daughter cells.
Meiosis provides an opportunity for recombination, whereas mitosis does not.
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.
In what stage of which type of cell division is the oocyte at the birth of a female mammal?
The oocyte is in G
of the mitotic cell cycle.
The oocyte is in metaphase of meiosis II.
The oocyte is in prophase of meiosis I.
The oocyte is in prophase of mitosis.
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.
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.
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.
Two copies of every gene in the genome are required for development, so loss of one of the copies from this region perturbs development.
What is the acrosomal reaction?
The acrosomal reaction is a repulsive interaction between the sperm and the egg.
The acrosomal reaction is the digestion of the acrosome by the sperm when it encounters an egg.
The acrosomal reaction is the digestion of the zona pellucida, permitting the sperm to contact the egg.
The acrosomal reaction is the entry of the sperm nucleus into the egg.
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
A layer of follicle-derived cells called cumulus cells
An extracellular layer of glycoproteins
The plasma membrane of the egg
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.
The cortical reaction is the entry of Ca
ions into the egg via the cortex, which initiates development.
The cortical reaction is the fusion of the egg cortex with the egg plasma membrane, which allows the sperm to enter.
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.
In humans, an individual with an XXY chromosomal complement will develop as
an individual with no secondary sexual characteristics.
Secretion of Müllerian-inhibiting substance by Sertoli cells
causes the Müllerian ducts to develop into the oviducts
causes the Müllerian ducts to develop into Wolffian ducts
causes the testis to produce testosterone
causes the Müllerian ducts to regress by apoptosis in males
The mammalian oviduct will form from the
In what way, if any, does the chromosomal determination of sex differ in
In humans, the Y chromosome determines maleness, with female development being a default state, but in
, the presence of two X chromosomes determines femaleness, and male development is the default state.
In humans, the Y chromosome determines maleness, but in
, the ratio of X chromosomes to autosomes determines maleness or femaleness.
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
There is no fundamental difference: in both organisms, the Y chromosome determines maleness.
The molecular activity of the Sex-lethal protein of
as a 'numerator', counting the number of X chromosomes
as a transcription factor
to control RNA splicing
to signal to the Tra receptor
GLP-1 protein involved in germ cell differentiation is similar to which mammalian signaling protein?
In mammals, dosage compensation is carried out by
decreasing the transcription of the X in males
increasing the transcription of the X in males
inactivating one X chromosome in females by condensation as heterochromatin
degrading one X chromosome in all female cells early in development
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