Answer: Meiosis I is a specialized form of cell division that involves the pairing of homologous chromosomes, crossing over, and reduction in chromosome number. It results in the formation of two haploid daughter cells that are genetically distinct from the parent cell. Meiosis I differs from mitosis in terms of chromosome pairing, genetic recombination, chromosome number, and independent assortment.
Step-by-step explanation:
In Meiosis I, the process of cell division occurs, resulting in the formation of two haploid cells. Here's a step-by-step explanation of what happens in Meiosis I:
1. Interphase: Before Meiosis I begins, the cell undergoes a period of growth and DNA replication during interphase, similar to the interphase of mitosis.
2. Prophase I: In this stage, the chromosomes condense and become visible under a microscope. Homologous chromosomes, which are pairs of chromosomes containing similar genes, come together and align side by side. This alignment is called synapsis, and the paired chromosomes form structures called tetrads or bivalents.
3. Crossing over: During synapsis, genetic material can be exchanged between non-sister chromatids of homologous chromosomes. This exchange is known as crossing over and results in the shuffling of genetic information between chromosomes. Crossing over contributes to genetic diversity among offspring.
4. Metaphase I: The tetrads line up along the equator of the cell. The spindle fibers attach to the centromeres of each chromosome, preparing for their separation.
5. Anaphase I: The homologous chromosomes separate and move toward opposite poles of the cell. Each chromosome still consists of two sister chromatids.
6. Telophase I: The separated chromosomes reach the poles of the cell, and a new nuclear membrane forms around each set of chromosomes. Cytokinesis then occurs, dividing the cell into two daughter cells.
At the end of Meiosis I, two daughter cells are formed, each containing one set of chromosomes. These cells are haploid, meaning they have half the number of chromosomes compared to the original cell. Additionally, each chromosome still consists of two sister chromatids.
Differences with mitosis:
1. Synapsis and crossing over: In Meiosis I, homologous chromosomes pair up and undergo crossing over, resulting in genetic recombination. This process does not occur in mitosis.
2. Reduction in chromosome number: Meiosis I reduces the chromosome number by half, resulting in haploid cells. Mitosis, on the other hand, produces two diploid cells, each with the same number of chromosomes as the parent cell.
3. Independent assortment: During Metaphase I, the homologous chromosomes line up randomly, leading to independent assortment. This random alignment contributes to genetic variation in the resulting daughter cells. In mitosis, chromosomes align in a specific order and do not undergo independent assortment.