Question

1. Crossing over is important because it _____.

a. allows the exchange of genes between homologous chromosomes

b. prevents variation in gametes

c. holds tetrads together

d. ensures that homologous chromosomes pair up

2. The M phase of mitosis and M phase of meiosis both occur after interphase. However, the two processes differ in the arrangement and behavior of their
chromosomes. How?

a. Homologous chromosomes pair up in mitosis, but not in meiosis.

b. The pairing up of homologous chromosomes and crossing over only occur during meiosis.

c. In meiosis, homologous chromosomes do not cross over; in mitosis, they do.

d. The centromeres of all chromosomes align on the metaphase plate in meiosis and on opposite sides of the metaphase plate in mitosis.

Answer 1

1) during meiosis homologous chromosomes pair up crossing over occurs between the non-sister chromatids of the sister chromatids, so alleles on the homologous chromosomes can be exchanged, this changes the allele combination in the chromatids, alleles are the variations of the genes, crossing over increases the genetic diversity of the gametes. so the answer is a) allows the exchange of genes between homologous chromosomes.

2) During meiosis, the homologous chromosomes pair up during prophase I but in mitosis, there is pairing up of homologous chromosomes, crossing over occurs between the non-sister chromatids of the paired homologous chromosomes. in meiosis-I, during metaphase the paired homologous chromosomes align along the metaphase plate, but during metaphase of mitosis the chromosomes align at the metaphase plate, so the answer is b) The pairing up of homologous chromosomes and crossing over only occur during meiosis.