Answer:
Allopatric speciation
Explanation:
Allopatric speciation refers to the geographic separation of a continuous genetic background, originating two or more new geographically isolated groups. These divergences of the original population might be related to migration in different directions, extinction of geographically intermediate populations, or geological events. During these events of speciation, emerging new barriers impede genetic flow between groups, as the two new populations that are separated can not get together and mate anymore. These barriers might be geographical or ecological.
Different stages are involved in the allopatric speciation process:
• The emergence of the barrier.
• Interruption in the genetic flow
• Slow and gradual differentiation due to the occurrence of mutations in each population and their accumulation in time.
• Genetic divergence by natural selection and reproductive isolation, impeding the two groups to mate even if the barrier disappears.
• Prezigotic isolation mechanisms favored by selection a secondary contact between the new species occurs.
The Panama isthmus is an example of allopatric speciation caused by an extrinsic geological barrier that interrupted the genetic flow between species driving to genetic changes and reproductive isolation.
Two different groups that evolved in allopatry might meet again in secondary contact if the barrier that separated them, disappears. In the Panama isthmus example, the groups that did mate, could not produce any fertile progeny because of postzygotic reproductive isolation. And the groups that did not mate, were not attracted to each other because of prezygotic reproductive isolation.
Answer:
The correct answer is option - d. Production of primary spermatocytes.
Explanation:
The accessory cells or supporting cells present within the seminiferous tubules of reproductive system termed as the Sertoli cells. They play various roles in the body and reproductive system.
Sertoli cells make blood-testis barrier in adjacent Sertoli cells in the seminiferous tubules. These cells secrete different types of enzymes and hormones such as inhibin which are also secreted by ovary and placenta in females. Sertoli cells produce seminiferous tubular fluid to provide nutrition to the sperm. Apoptotic germ cells are timely eliminated by these cells.
Thus, the correct answer is option D. Production of primary spermatocytes.
Answer:
The answer is D a retrovirus inserts DNA into the host cells genes
