Question

21 ) in humans, which cell is produced most directly by mitotic cell division?
a ) a sperm cell \tc ) a skin cell
b ) an egg cell \td ) a zygote
22 ) which event normally occurs in meiosis but not in mitosis?
a ) chromosome replication
b ) nuclear membrane disintegration
c ) synapsis of homologous chromosomes
d ) movement of chromosomes to opposite poles
23 ) which situation is a result of crossing - over during meiosis?
a ) genes are duplicated exactly, ensuring that offspring will be identical to the parents
b ) genes are rearranged, increasing the variability of offspring.
c ) chromatids thicken and align themselves, helping to ensure genetic continuity
d ) chromatids fail to sort independently, creating abnormal chromosome numbers
24 ) in sexually reproducing species, doubling of the chromosome number from generation to generation is prevented by events that take place during the process of
a ) gametogenesis \tc ) cleavage
b ) nondisjunction \td ) fertilization
25 ) the diagrams to the right represent the gametes and zygotes associated with two separate fertilizations in a particular species. the abnormal zygote is most likely the result of?
a ) polyploidy
b ) chromosome breakage
c ) nondisjunction
d ) gene linkage
26 ) the restoration of the species number of homologous chromosomes occurs during
a ) the formation of male sex cells
b ) replication of centromeres
c ) fertilization of an egg by a sperm
d ) migration of single - stranded chromosomes
27 ) the diagram to the right shows stages in the life cycle of a unicellular flagellated green alga. the process that most likely takes place between stages e and a is
a ) mitosis
b ) fertilization
c ) meiosis
d ) cleavage

Explanation:

Question 21

In humans, meiosis occurs in germ cells (like sperm and egg cells) to produce gametes. A sperm cell is a male gamete produced by meiosis (specifically, spermatogenesis). An egg cell is also a gamete from meiosis, but the question asks which cell is produced directly by meiosis - male cell division (spermatogenesis) produces four sperm cells directly from meiosis, while egg cell production (oogenesis) has unequal division. Skin cells and zygotes undergo mitosis, not meiosis. So the sperm cell is produced directly by meiosis (male cell division).

Meiosis has unique events like synapsis (pairing of homologous chromosomes) and crossing - over, which do not occur in mitosis. Chromosome replication happens in both before meiosis I and mitosis. Nuclear membrane disintegration occurs in both during prophase. Movement of chromosomes to opposite poles occurs in both anaphase of mitosis and anaphase I/II of meiosis. So synapsis of homologous chromosomes is unique to meiosis.

Crossing - over during meiosis (prophase I) involves the exchange of genetic material between homologous chromosomes. This rearranges genes, increasing genetic variability in offspring. Option a is wrong as crossing - over doesn't duplicate genes exactly (and offspring aren't identical to parents in sexual reproduction). Option c describes events in mitosis/meiosis but not crossing - over. Option d is nondisjunction, not crossing - over.

Answer:

a. a sperm cell

Question 22