Purpose: Meiosis is a special variation of cell department that occurs only in the testes and also ovaries; the organs that develop the male and female reproductive cells; the sperm and eggs. Why is this different? Ordinary body cells have actually a finish collection of chromosomes. If body cells from mom and dad fsupplied to develop a baby, the fertilized egg would certainly have twice as many chromosomes as it should. Meiosis is occasionally called "reduction division" because it reduces the variety of chromosomes to fifty percent the normal number so that, once fusion of sperm and also egg occurs, baby will certainly have the correct number. Because of this the purpose of meiosis is to produce gametes, the sperm and eggs, through fifty percent of the hereditary match of the parent cells. In the numbers below, pink represents a genetic contribution from mommy and also blue represents a genetic contribution from dad. In this instance, a diploid body cell consists of 2n = 4 chromosomes, 2 from mom and also 2 from dad. In human beings, 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 alongside each other. This is called synapsis. Homologous chromosomes contain the corresponding alleles donated from mother and father. This is also once meiotic recombicountry, additionally know as "crossing over" (watch below) occurs. This process allows for a hereditary shuffling of the attributes of the 2 paleas, creating an almost unlimited range of feasible combicountries. See the close-up diagram below.

Anaphase I: Instead of chromatids dividing at the centromere, homologous chromosome pairs (now shuffled by crossing over) relocate alengthy the spindle fibers to opposite poles.

Telophase I: The cell pinches and also divides.

Meiosis II

Prophase II: It is visibly evident that replication has actually not arisen.

Metaphase II: The paired chromosomes line up.

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

Telophase II: The cells pinch in the facility and also divide aobtain. The last outcome is 4 cells, each via half of the hereditary material found in the original. In the instance of males, each cell becomes a sperm. In the situation of females, one cell becomes an egg and the various other 3 end up being polar bodies which are not used.

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Meiotic Recombination (Crossing over):

Your parents each have at least one pair of alleles (versions of a gene) for eexceptionally trait (and many kind of pairs of alleles for each polygenic trait). You finished up via half of mom"s paired genes and also half of dad"s paired genes. But each non-identical-twin son of these paleas ends up through a different combicountry. Imagine, for example, that eye color was managed by a solitary gene, and also that mom could have B, the allele for brvery own eyes or b, the allele for blue eyes, and also dad could additionally have B or b. This leads to four possibilities: You could get B from mom and B from dad, or B from mother and also b from dad, or b from mommy and B from dad, or b from mommy and also b from dad. Each sperm and egg will finish up via either B or b from mother and either B or b from dad. It"s a flip of the coin. But this happens individually for each trait, so just because you acquired your dad"s brvery own eyes does not suppose you"ll obtain his blond hair too. Each sibling is 50% mom and 50% dad, yet which 50% of each have the right to differ in the siblings. This shuffling process is recognized as recombination or "crossing over" and occurs while the chromome pairs are lined up in Metaphase I.