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Body cells are produced by mitosis. But sperm and egg cells do not form this way. Reproductive cells are formed by meiosis. Each gamete has only half the usual number of chromosomes, and they are referred to as monoploid or haploid. Then when the sperm and egg join, the zygote has the full number of chromosomes: two of each, and the cell is referred to as diploid.
Meiosis in males produces four functional, unique sperm cells. This process happens rapidly in all parts of the testes, so much so that 1000 sperm can be formed every second.
Meiosis in females produces four cells, but only one functional, unique egg cell. When the cell divisions occur, most of the organelles and nutrients are transferred to one cell so that it is strong and healthy enough to survive when fertilized until the mother's uterus can support it. One of these big strong eggs is released each month, a process called ovulation.
Every gamete contains a combination of traits that has NEVER existed before. This is made possible during meiosis because of the process of CROSSING OVER.
During the first metaphase of meiosis, HOMOLOGOUS PAIRS of chromosomes are lined up next to each other at the equator of the cell. This is different than metaphase in mitosis, where all chromosomes line up single-file at the equator.
Remember, each x-shaped structure is made up of two identical copies of the same piece of DNA. Each copy is called a chromatid. When the pair of “double” chromosomes are next to each other, they briefly come in contact and exchange pieces of themselves. This phenomenon is called crossing over. This process produces the incredible amount of variation present in sexually reproducing species.
Meiosis Diagrams.pdfReport abuse