In the quest to understand the basis of infertility in humans, researchers have identified a mutation in a gene associated with chiasmata. This protein normally acts to promote homologous recombination. Why might a defect in homologous recombination have consequences for fertility?A. The chiasmata halts the whole process of meiosis, if crossover do not form properly. B. Crossover formation is a necessary step in meiosis I to ensure proper chromosome segregationC. A checkpoint requires a certain level of genetic variability for meiosis to proceed. D. Chiasmata are the connections between the centromeres and the centromeres that pull them to each pole of the daughter cells.

B. Crossover formation is a necessary step in meiosis I to ensure proper chromosome segregation

Explanation:

Crossing-over is a unique phenomenon that occurs in the prophase I stage of meiosis I, where non-sister chromatids of homologous chromosomes exchange their chromosomal segment. The physical point where this exchange occurs is called CHIASMATA. Hence, a mutation that affects the gene associated with the chiasmata will affect the occurrence of crossing over or homologous recombination.

Crossing-over, through the formation of the chiasmata, is responsible for the physical alignment and proper segregation of chromosomes into gametes. Naturally, the chiasmata formed as a result of recombination during meiosis helps ensure that the chromosomes stay together until it is the right time to separate. This way, any chromosomal defect in the resulting gamete is prevented.

However, an error or defect in homologous recombination might give rise to gametes with chromosomal disorder, a condition known as ANEUPLOIDY i.e. missing or additional chromosomes in gametes. This can affect the fertility of the involved human.