Question

Because synapsis of chromosomes in meiotic tissue is often accompanied by crossing over, it would be detrimental to sex-determining mechanisms to have sex-determining loci on the Y chromosome transferred, through crossing over, to the X chromosome. True or False?

Answer 1

The statement about detrimental effects of sex-determining loci being transferred between X and Y chromosomes through crossing over is true. Such transfer could disrupt sex-determination, hence crossing over between these chromosomes is limited to small homologous regions to prevent such issues.

Step-by-step explanation:

The statement is true. Sex-determining mechanisms in humans rely on the correct pairing and segregation of the sex chromosomes, X and Y. During meiosis, specifically in prophase I, the X and Y chromosomes pair up, forming a partial synaptonemal complex to facilitate synapsis.

Synapsis often leads to crossing over or the exchange of genetic material, which occurs between homologues. However, significant crossing over between the X and Y chromosomes is prevented because they are largely non-homologous, except for a small region of homology that allows pairing.

This minimal crossing over ensures the integrity of the sex chromosomes, so sex-determining loci are not wrongly transferred between them. Excessive or inappropriate recombination can lead to disorders like Turner syndrome or Klinefelter syndrome, which results from nondisjunction, further highlighting the importance of controlled recombination.