Answer to Question 1
Correct Answer: 1
Rationale 1: Not all same-sex twins are identical or monozygotic, because fraternal, or dizygotic, twins can be the same gender or different genders.
Rationale 2: When the zygote splits, identical twins share the same genotype result.
Rationale 3: The only way to have twins of different genders is if they came from two separate fertilized ova. Monozygotic twins are identical and are the same gender.
Rationale 4: Monoamnionic-monochorionic twins are very rare and occur as a result of the zygote splitting seven or more days after fertilization.
Answer to Question 2
Correct Answer: 3
Rationale 1: Males begin spermatogenesis at puberty and continue throughout their life. Each sperm divides into four haploid cells.
Rationale 2: Females are born with all the ova they will ever produce. The ova begin to be formed in early fetal life. One ovum is released each month during the reproductive life of a female, from menarche to menopause.
Rationale 3: Each ovum undergoes meiotic division just prior to being released from the graafian follicle. Each cell created by this meiosis has the same number of chromosomes, but the cytoplasm does not split equally. This causes a polar body to be produced along with a secondary oocyte.
Rationale 4: Primary spermatocytes contain 46 chromosomes (46XY). Each primary spermatocyte undergoes meiotic division into two haploid secondary spermatocytes (22X or 22Y). Haploid cells each contain half of the genetic material of the original cell. Then each secondary spermatocyte undergoes a second meiotic division into two haploid spermatids (remaining either 22X or 22Y.) Spermatids mature into spermatozoa. Thus, a primary spermatocyte eventually becomes four haploid spermatozoa.