What happens during cell division and crossover according to the brief below

Question

The human body consists of billions of cells, of which a large percentage is being
replaced every day (Fischetti et al., 2021). These cells are of two distinct kinds: body cells
and germ cells (eggs and sperm). The process of cell division is a crucial step in the
formation of a new life. (See Figure 2.2.)
The body cells (or somatic cells) in the zygote divide through the process known as
mitosis. The goal of mitosis is to duplicate one cell into two genetically identical cells.
Before entering mitosis, a cell must first go through an interphase where the cell grows,
copies its DNA, and prepares for division. Mitosis occurs in four phases, during which
each of the 46 chromosomes (23 paternal cells and 23 maternal cells) divides lengthwise
into two, resulting in 92 chromosomes. The one half of each pair then moves to opposite
poles of the cell. The cell then divides, resulting in two new cells that are identical to the
original cell. Therefore, these cells contain 46 chromosomes and have the same genetic
information as the original cell. The process continues to replicate to eventually form body
parts and organs for the body that is you. The germ cells divide through a process known as meiosis. Before meiosis starts,
an interphase occurs, as in mitosis. In meiosis, a special cell division reduces the cell from
two sets of chromosomes to a single set of chromosomes. Meiosis occurs in two stages,
meiosis I and meiosis II, each of which occurs in four phases. During this process, the two members of each chromosome pair separate and move to opposite poles of the cell. Cell
division occurs to eventually form cells with 23 chromosomes that do not necessarily have
the same genetic information as the original germ cell. These cells are the gametes or
sex cells and are formed in the testes in the case of a male, and in the ovaries in the case
of a female.
An interesting phenomenon that occurs during the first phase of meiosis I is a process
known as crossover (Encyclopaedia Britannica, 2021). Crossover occurs when sections
of homologous chromosomes (chromosomes that form a pair) exchange chromosome
segments and therefore, also genes. The exchange takes place because of, and during, the
direct contact between homologous chromosomes and is also referred to as homologous
reorganisation. This crossover of genetic material not only enhances the uniqueness of
the gamete's genetic composition, but also increases the variation within the available
genetic material.

Answer 1

During cell division, the processes of mitosis and meiosis take place, each serving distinct roles in the life cycle of the organism.

Mitosis is the process by which somatic (body) cells divide. It consists of several stages that follow an initial interphase, where the cell prepares for division by growing and replicating its DNA. Mitosis involves four main phases:

1. Prophase: Chromosomes condense and become visible, and the nuclear envelope breaks down.
2. Metaphase: The chromosomes align at the cell's equatorial plate.
3. Anaphase: The sister chromatids of each chromosome are pulled apart to opposite poles of the cell.
4. Telophase: Nuclear membranes start to form around the two sets of separated chromosomes, and the cell prepares to divide.

After these phases, the cell undergoes cytokinesis, leading to the formation of two genetically identical daughter cells, each containing 46 chromosomes (23 pairs from the mother's and father's genetic contributions).

Meiosis, on the other hand, is the specialized process for the formation of germ cells (gametes, such as sperm and eggs) and involves two rounds of cell division, known as meiosis I and meiosis II, after an interphase. This process results in gametes with half the number of chromosomes (23), ensuring that when fertilization occurs, the resulting zygote has the correct diploid number of chromosomes.

In meiosis I, homologous chromosomes (each consisting of two sister chromatids) pair up and may exchange segments in a phenomenon called crossover (or homologous recombination). This occurs during prophase I:

• The chromosomes physically align and can form structures called chiasmata at points of contact.
• Sections of the chromatids may be exchanged between homologous chromosomes, leading to new combinations of genes. This increases genetic diversity among the gametes, contributing to the variation in traits within a population.

After meiosis I, the two homologous chromosomes separate, followed by meiosis II, where the sister chromatids are divided, ultimately producing four non-identical gametes, each with 23 chromosomes. This process of crossover and genetic variation is crucial for evolution and the adaptability of species.