Question 1

What is the consequence of synapsis and crossing over?
A)Pure segregation of alleles along the metaphase plate
B)Tetraploidy, in which there are four copies of each chromatid
C)Diploidy of chromosome number and haploidy for DNA content
D)Random recombination of genetic material between paternal and maternal chromatids

Accepted Answer

Synapsis allows the homologous chromosomes with four chromatids to remain in contact down the lengths of the chromatids for both the maternal and paternal chromosomes of the tetraploid pair in the early gamete. This results in a huge but usually even "shuffling" of genetic material so that at the end of the pachytene stage, the two chromosomes (with two chromatids each) are now combinations of maternal and paternal genes, rather than one pure maternally derived chromosome and one pure paternally derived chromosome. This allows for any one person to receive bits and pieces of genetic material in combination from many parental ancestors.

Question 2

How many mature ovum result from the complete oogenesis of one oogonium?
A)One
B)Two
C)Three
D)Four

Accepted Answer

Complete oogenesis is the process of forming a mature ovum from a precursor female germ cell known as oogonium. Unlike spermatogenesis, in which one precursor male germ cell normally produces four spermatocytes, only one ovum is produced by this process, with up to three polar bodies also produced.

Question 3

Which cell division process sequences are normal for meiosis for gametogenesis?
A)Two rounds of DNA synthesis each followed by a separate round of meiotic cell division
B)Two rounds of DNA synthesis followed by two progressive rounds of meiotic cell division
C)A single round of DNA synthesis followed by two separate rounds of meiotic cell division
D)A single round of DNA synthesis first preceded by one round of meiotic cell division and then followed by a final round of meiotic cell division

Accepted Answer

Explaimation: Cell division of meiosis for gametogenesis is a special type of cell division in which the chromosome number per cell is reduced to half and occurs only in germ cells. It involves only one episode of DNA synthesis that is followed, over time, by two separate rounds of meiotic cell divisions.

Question 4

Why is normal fertilization of one mature ovum usually performed by only one mature sperm even though hundreds of millions of sperm are present in the seminalfluidofone ejaculation?
A)The corona radiata causes the tail of the other sperm to fall off, decreasing their motility.
B)At the time of first penetration, the pH around the ovum changes, and the enzymes of the other sperm are inactivated.
C)Fusion of the two nuclei forms a tight nuclear membrane that prevents the nuclei of other sperm from entering.
D)After being penetrated by one sperm, the ovum's membrane changes electrically and prevents other sperm from entering.

Accepted Answer

When the sperm binds with and then penetrates the plasma membrane of the ovum, several different processes occur. First, the ovum's plasma membrane changes its electrical charge, preventing any other sperm from entering. Only the fertilizing sperm's tail and midsection drop off and do not enter the ovum; the other sperm remain motile but cannot penetrate the ovum's plasma membrane. It is not the nuclear membrane that prevents two (dispermy) or more sperm from fertilizing a single ovum. Although the pH of fluid in the female reproductive tract can inhibit acrosomal enzyme activity, this is not what prevents dispermic fertilization.

Question 5

Meiosis II of oocytes is completed at which developmental period?
A)At the ninth prenatal week
B)During puberty
C)At ovulation
D)At fertilization

Accepted Answer

Completion of meiosis I of the primary oocyte into a secondary oocyte and a polar body does not happen until just before ovulation. Meiosis II of the secondary oocyte is completed only if fertilization takes place.

Question 6

During which phase of gametogenesis is the process of crossing over more likely to occur for either spermatocytes or oocytes?
A)Metaphase I
B)Interphase I
C)Anaphase I
D)Prophase I

Accepted Answer

Crossing over is the lengthening and touching of the chromatids that allows for pieces of sister chromatids to be exchanged. For both spermatogenesis and oogenesis, the process occurs during prophase I, although the timing differs between the two processes.

Question 7

Why is meiosis II for both spermatogenesis and oogenesis called an "equatorial division?"
A)The amount of cytoplasm in the secondary sex cells is evenly divided among the final cells.
B)The actual number of chromosomes within the resulting cells is the same as before this division.
C)Crossing over stops, and the bivalent chromosomes coil and condense in preparation for segregation.
D)The division of both the two secondary spermatocytes and the two secondary oocytes results in a total of eight gametes.

Accepted Answer

For both ova and sperm, meiosis II is a relatively rapid process. This division is an equational division because the number of chromosomes remains the same (23), although the DNA content was diploid before the division and haploid after the division.

Question 8

Which cell in the process of oogenesis has the most chromosomes?
A)Mature ovum
B)Primary oocyte
C)Secondary oocyte
D)Polar body

Accepted Answer

The primary oocyte first starts oogenesis by entering the cell cycle and proceeding through S phase with DNA replication, which results in tetraploidy or a 4N state. The mature ovum and polar bodies are haploid, containing only 1N of chromosomes. The secondary oocyte has undergone meiosis I and is 2N.

Question 9

What is the usual outcome of "crossing over" during meiosis I for both spermatogenesis and oogenesis?
A)Unequal division of DNA between two new daughter cells during nucleokinesis
B)Mixing of maternal and paternal genes within one chromosome pair
C)Unequal distribution of cytoplasmic material
D)More rapid progression to meiosis II

Accepted Answer

In gametogenesis, crossing over occurs when the four chromatids of each chromosome pair are lined up lengthwise and touch; the exchanges of chromosome material occur through breaks and rearrangements. The exchanges occur not just between chromatids from one parent but also among the four chromatids for both the maternal and paternal chromosomes of the pair. The result is a huge "shuffling" of genetic material, so at the end of the pachytene stage, the two chromosomes (with two chromatids each) are now combinations of maternal and paternal genes, rather than one purely maternal-derived chromosome and one purely paternal-derived chromosome.

Question 10

Which response is the immediate and direct result of fertilization?
A)Gamete chromosome reduction to the haploid number
B)Rapid proliferation of acrosomal and coronal cells
C)Primary sex determination of the zygote
D)Nuclear condensation

Accepted Answer

At fertilization, the union of one mature haploid sperm with one mature haploid ovum occurs to form a diploid zygote. One sex chromosome is provided by the spermatocyte, and one is provided by the mature ovum, determining the primary or "genetic" sex of the new zygote. The nucleus increases in size and does not condense at this time. The gametes are haploid long before fertilization occurs. Changes in the acrosome of the spermatocyte and coronal cells of the ovum also occur before fertilization, not after.

Question 11

Which process is unique to spermatogenesis?
A)Synapsis during the zygotene stage
B)Equal distribution of cytoplasm during meiosis I
C)Elongation of chromatids during the diplotene stage
D)Degeneration of germ cells between fetal life and the onset of puberty

Accepted Answer

In oogenesis the first meiotic cell division results in the unequal distribution of cytoplasmic fluid and all organelles into the secondary oocyte. As a result, the first polar body contains very little of these elements. By the end of meiosis II, only the mature ovum has cytoplasm. In spermatogenesis, the cytoplasm and all its elements are evenly distributed to the secondary spermatocytes (and eventually to the four spermatids). Synapsis occurs during the zygotene stage of both spermatogenesis and oogenesis. Chromatid elongation occurs in the leptotene stage. Degeneration of germ cells between fetal life and the onset of puberty occurs only in oogenesis.

Question 12

Why is fertilization of a polar body unlikely to lead to normal embryonic and fetal development?
A)The resulting zygote would be 4N instead of 2N.
B)The lack of cytoplasm would inhibit cellular reproduction.
C)The polar body has spent too long of a time trapped in meiosis I.
D)The resulting zygote would be smaller, which increases the risk for apoptosis.

Accepted Answer

Polar bodies are haploid (1N) and, in theory, could be fertilized to form a zygote. However, because both mature sperm and polar bodies are almost completely deficient in cytoplasm and mitochondria, any fertilized polar body would not have the energy or the intracellular machinery to direct normal development.

Quiz 3: Genetic Influence on Cell Division, Differentiation, and Gametogenesis

What is the consequence of synapsis and crossing over?

How many mature ovum result from the complete oogenesis of one oogonium?

Which cell division process sequences are normal for meiosis for gametogenesis?

Why is normal fertilization of one mature ovum usually performed by only one mature sperm even though hundreds of millions of sperm are present in the seminalfluidofone ejaculation?

Meiosis II of oocytes is completed at which developmental period?

During which phase of gametogenesis is the process of crossing over more likely to occur for either spermatocytes or oocytes?

Why is meiosis II for both spermatogenesis and oogenesis called an "equatorial division?"

Which cell in the process of oogenesis has the most chromosomes?

What is the usual outcome of "crossing over" during meiosis I for both spermatogenesis and oogenesis?

Which response is the immediate and direct result of fertilization?

Which process is unique to spermatogenesis?

Why is fertilization of a polar body unlikely to lead to normal embryonic and fetal development?