how does the process of crossing over results in genetic variability in an organism due to meiotic cell division?
crossing over is when the homologous chromosomes pair up on the metaphase plate during meiosis 1, the homologous chromosomes swap short bits of dna. This is one of the sources of genetic variation in the offspring and one of the principle mechanisms of evolution. In more simple terms; the an individual inherits homologous chromosomes from their parents, except if the species is one like humans in which there is an xy difference on the sex chromosomes. During meiosis these chromosomes are duplicated and line up next to each other in the middle of the dividing reproductive cell (thats important, this only happens in reproductive cells! somatic cells (all the others) go through mitosis) After crossing over, they are pulled apart into two intermediary cells in which each has a duplicate set of chromosomes. These are called sister chromatids. They line up on the metaphase plate (the equator of the cell) of meiosis 2 just like what happened during meiosis 1. The sister chromatids are split apart and pulled to the two poles of the cell, which divides again, resulting in a total of 4 reproductive cells, each containing a half chromosome count of what the somatic cells all have. When two organisms reproduce, their reproductive cells fuse forming an embryo, which brings the chromosome count back to full. Once the organism has reached sexual maturity this process is repeated, producing new chromosomes that are different from the ones passed on from their parents. The source of this variation is the crossing over on metaphase plate 1 and the random assortment of the sister chromatids on metaphase plate 2. Hope this was helpful.
crossing over is when the homologous chromosomes pair up on the metaphase plate during meiosis 1, the homologous chromosomes swap short bits of dna. This is one of the sources of genetic variation in the offspring and one of the principle mechanisms of evolution. In more simple terms; the an individual inherits homologous chromosomes from their parents, except if the species is one like humans in which there is an xy difference on the sex chromosomes. During meiosis these chromosomes are duplicated and line up next to each other in the middle of the dividing reproductive cell (thats important, this only happens in reproductive cells! somatic cells (all the others) go through mitosis) After crossing over, they are pulled apart into two intermediary cells in which each has a duplicate set of chromosomes. These are called sister chromatids. They line up on the metaphase plate (the equator of the cell) of meiosis 2 just like what happened during meiosis 1. The sister chromatids are split apart and pulled to the two poles of the cell, which divides again, resulting in a total of 4 reproductive cells, each containing a half chromosome count of what the somatic cells all have. When two organisms reproduce, their reproductive cells fuse forming an embryo, which brings the chromosome count back to full. Once the organism has reached sexual maturity this process is repeated, producing new chromosomes that are different from the ones passed on from their parents. The source of this variation is the crossing over on metaphase plate 1 and the random assortment of the sister chromatids on metaphase plate 2. Hope this was helpful.
During meiotic cell division, crossing over occurs during the pairing of homologous chromosomes on the metaphase plate of meiosis 1. This process involves the swapping of small segments of DNA between the homologous chromosomes. Crossing over is one of the sources of genetic variability in offspring and is a principal mechanism of evolution.
To understand how crossing over results in genetic variability, let’s break down the steps of meiotic cell division:
1. Inheritance of homologous chromosomes: An individual inherits homologous chromosomes from their parents, with the exception of species like humans that have an XY difference on the sex chromosomes.
2. Duplication and alignment of chromosomes: During meiosis, the chromosomes are duplicated, resulting in two copies of each chromosome. The duplicated chromosomes then line up next to each other in the middle of the dividing reproductive cell. Importantly, meiosis only occurs in reproductive cells, while somatic cells undergo mitosis.
3. Crossing over: During meiosis 1, crossing over occurs between the paired homologous chromosomes on the metaphase plate. Short segments of DNA are exchanged between the chromosomes. This process leads to the combination of genetic information from both parent chromosomes, resulting in genetic variability in offspring.
4. Separation and division: After crossing over, the paired homologous chromosomes are pulled apart, resulting in two intermediary cells. Each intermediary cell contains a duplicate set of chromosomes called sister chromatids. These sister chromatids then line up on the metaphase plate of meiosis 2, similar to what happened during meiosis 1.
5. Chromosome separation: During meiosis 2, the sister chromatids are split apart and pulled to the two poles of the cell. The cell then divides again, resulting in a total of four reproductive cells, each containing a half chromosome count compared to somatic cells.
6. Reproduction and offspring: When two organisms reproduce, their reproductive cells fuse, forming an embryo. This fusion brings the chromosome count back to the full count. Once the organism reaches sexual maturity, this process is repeated, producing new chromosomes that are different from the ones passed on from their parents.
In summary, crossing over during meiotic cell division contributes to genetic variability by exchanging genetic material between homologous chromosomes. This, in combination with the random assortment of sister chromatids on the metaphase plate, results in different combinations of genes in the reproductive cells, leading to genetic diversity in offspring and ultimately contributing to the principle of evolution.