Purpose: Meiosis is a unique version of cell division that occurs only in the testes and also ovaries; the organs that produce the male and also female refertile cells; the sperm and eggs. Why is this different? Ordinary body cells have actually a complete collection of chromosomes. If body cells from mother and also dad fsupplied to create a baby, the fertilized egg would certainly have twice as many type of chromosomes as it need to. Meiosis is periodically referred to as "reduction division" bereason it reduces the variety of chromosomes to half the normal number so that, once fusion of sperm and also egg occurs, baby will have the correct number. Because of this the purpose of meiosis is to develop gametes, the sperm and eggs, with half of the genetic enhance of the parent cells. In the figures below, pink represents a genetic contribution from mommy and blue represents a hereditary contribution from dad. In this example, a diploid body cell has 2n = 4 chromosomes, 2 from mommy and two from dad. In people, 2n = 46, and n = 23.

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Meiosis I


Meiosis II

Meiosis I

Interphase I: Identical to Interphase in mitosis.

Prophase I: Identical to Prophase in mitosis.

Metaphase I: Instead of all chromosomes pairing up alengthy the midline of the cell as in mitosis, homologous chromosome pairs line up beside each other. This is called synapsis. Homologous chromosomes contain the matching alleles donated from mom and also father. This is also once meiotic recombicountry, additionally recognize as "crossing over" (watch below) occurs. This procedure permits for a genetic shuffling of the qualities of the 2 parental fees, developing an practically unlimited variety of feasible combicountries. See the close-up diagram below.

Anaphase I: Instead of chromatids splitting at the centromere, homologous chromosome pairs (currently shuffled by crossing over) relocate along the spindle fibers to oppowebsite poles.

Telophase I: The cell pinches and divides.

Meiosis II

Prophase II: It is visibly noticeable that replication has actually not developed.

Metaphase II: The paired chromosomes line up.

Anaphase II: The chromatids split at the centromere and also move alengthy the spindle fibers to oppowebsite poles.

Telophase II: The cells pinch in the center and divide aacquire. The last outcome is four cells, each through fifty percent of the hereditary product found in the original. In the case of males, each cell becomes a sperm. In the case of females, one cell becomes an egg and also the various other 3 become polar bodies which are not supplied.

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Meiotic Recombination (Crossing over):

Your paleas each have at least one pair of alleles (versions of a gene) for eincredibly trait (and many kind of pairs of alleles for each polygenic trait). You ended up through half of mom"s paired genes and also half of dad"s paired genes. But each non-identical-twin boy of these parental fees ends up via a different combination. Imagine, for example, that eye shade was managed by a single gene, and also that mommy might have actually B, the allele for brown eyes or b, the allele for blue eyes, and dad could additionally have actually B or b. This leads to four possibilities: You might gain B from mother and also B from dad, or B from mother and b from dad, or b from mom and B from dad, or b from mommy and also b from dad. Each sperm and egg will certainly finish up through either B or b from mom and also either B or b from dad. It"s a flip of the coin. But this happens individually for each trait, so simply because you acquired your dad"s brvery own eyes does not intend you"ll obtain his blond hair also. Each sibling is 50% mommy and also 50% dad, yet which 50% of each deserve to vary in the siblings. This shuffling procedure is well-known as recombination or "crossing over" and also occurs while the chromome pairs are lined up in Metaphase I.