Crossing over does not occur during mitotic cell division. It is a process that happens during meiosis, a different type of cell division. Understanding this difference is important for comprehending how genetic information is passed from one generation to the next and how genetic diversity arises.
The Purpose of Mitosis
Mitosis is a process of cell division where a single parent cell divides into two identical daughter cells. This process is for growth, repairing damaged tissues, and replacing worn-out cells. Skin cells and cells lining the digestive tract undergo mitosis to renew themselves.
The goal of mitosis is to ensure genetic fidelity, so each new daughter cell receives an exact copy of the parent cell’s genetic material. This duplication maintains the chromosome number and genetic consistency across cell generations. Since the aim is to create genetically identical cells, new genetic combinations are not introduced during mitosis.
Understanding Genetic Crossover
Genetic crossing over, also known as recombination, involves the exchange of genetic material. This exchange occurs between homologous chromosomes, which are pairs of chromosomes carrying the same genes but originating one from each parent. The process leads to new combinations of alleles, or different forms of a gene, on the chromosomes.
The mechanism of crossing over involves homologous chromosomes aligning closely in a process called synapsis. While paired, segments of non-sister chromatids can break and rejoin to the other chromosome. The points where this exchange occurs are visible as chiasmata. This shuffling creates new combinations of genes that were originally located on the same chromosome.
Meiosis: Where Crossover Actually Happens
Crossing over is an event of meiosis, a type of cell division that produces gametes, such as sperm and egg cells, for sexual reproduction. Unlike mitosis, meiosis results in cells with half the number of chromosomes of the parent cell, ensuring that when two gametes fuse during fertilization, the offspring will have the correct chromosome number.
This genetic exchange takes place during Prophase I of meiosis. During this phase, homologous chromosomes pair up and form structures called tetrads, consisting of four chromatids. It is within these paired structures that crossing over occurs, facilitating the exchange of genetic segments between non-sister chromatids.
The resulting recombinant chromosomes contain a mix of genetic information from both parental chromosomes. This process contributes to genetic variation within a species, as it generates combinations of alleles in the gametes. This diversity is important for adaptation and evolution, contrasting with mitosis where genetic identity is preserved.