1. Crossing over occurs during meiosis, which results in the exchange of genetic material. This leads to the formation of genetically diverse gametes at the end of meiosis.
Further Explanation:
When a single cell undergoes division twice to produce four-cell, each containing half the number of chromosomes as the parent cell, the process is called meiosis. Meiosis occurs in germ cells such as eggs and sperms in females and males, respectively. It is divided into two stages: meiosis I and meiosis II. Meiosis I involves interphase as the first stage during which DNA replication occurs. The next stage is prophase I, in which the chromosomes condense to form an X-shaped structure. This structure contains two sister chromatids from each chromosome of the pair. The genetic information is exchanged between the pair of homologous chromosomes through crossing over or recombination. This is followed by metaphase I in which the homologous chromosomes align at the center. In anaphase I, the homologous pair separates and moves in the opposite direction while keeping the sister chromatids intact. Cytokinesis occurs in telophase I. In this phase; the parent cell pinches into two daughter cells that start meiosis II. It includes stages like prophase II, metaphase II, anaphase II, and telophase II. These stages lead to the formation of four haploid gametes. These gametes show genetic variation due to recombination.
The process of mitosis comprises the division of a single cell into two similar cells containing the same chromosome number as the original cell. Mitosis also involves similar stages, such as interphase, prophase, metaphase, anaphase, and telophase. But it does not include the exchange of genetic material during prophase. Therefore, at the end of mitosis, cells with similar genetic makeup are formed.
2. Prophase stage of meiosis I include crossing over because of which genetic variation increases in the gametes produced.
Further Explanation:
Crossing over is a process in which equal segments of chromosomes are transferred in a homologous pair. It takes place during meiosis in the prophase I stage. In this stage, the chromosomes have duplicated and the sister chromatids have formed. At a point, the two homologous chromosomes come together and form a synapse. During synapse, breakage occurs in one chromatid from each pair of the homologous chromosomes. The exchange of genes occurs at the broken segments to form a new combination of genes. This results in the formation of new gene pairs in the corresponding chromosome. When the sister chromatids are separated in meiosis II, gametes are formed in which some gametes contain newly formed genetic composition while some contain inherited genes. Therefore, crossing over enhances variation in genetic makeup.
