Purpose: Meiosis is a special version of cell department that occurs only in the testes and ovaries; the guts that develop the male and female reproductive cells; the sperm and eggs. Why is this different? ordinary body cells have actually a complete collection of chromosomes. If human body cells native mom and dad fused to kind a baby, the fertilized egg would have actually twice as plenty of chromosomes as it should. Meiosis is sometimes called "reduction division" since it reduces the number of chromosomes to fifty percent the normal number therefore that, when blend of sperm and egg occurs, infant will have actually the correct number. Because of this the function of meiosis is to produce gametes, the sperm and also eggs, with fifty percent of the genetic complement of the parental cells. In the figures below, pink to represent a genetic contribution from mom and blue to represent a genetic contribution native dad. In this example, a diploid human body cell includes 2n = 4 chromosomes, 2 from mom and also two from dad. In humans, 2n = 46, and n = 23.

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Meiosis I


Meiosis II

Meiosis I

Interphase I: the same to Interphase in mitosis.

Prophase I: similar to Prophase in mitosis.

Metaphase I: rather of all chromosomes pairing up follow me the midline the the cell as in mitosis, homologous chromosome pairs line up next to each other. This is dubbed synapsis. Homologous chromosomes save on computer the corresponding alleles donated from mother and father. This is also when meiotic recombination, likewise know as "crossing over" (see below) occurs. This process allows for a hereditary shuffling of the qualities of the two parents, producing an nearly infinite range of feasible combinations. Check out the close-up diagram below.

Anaphase I: instead of chromatids splitting at the centromere, homologous chromosome pairs (now shuffled by cross over) move along the spindle fibers to the contrary poles.

Telophase I: The cell pinches and also divides.

Meiosis II

Prophase II: it is visibly noticeable that replication has actually not occurred.

Metaphase II: The paired chromosomes line up.

Anaphase II: The chromatids separation at the centromere and migrate follow me the spindle fibers to the contrary poles.

Telophase II: The cell pinch in the center and also divide again. The last outcome is four cells, every with half of the hereditary material discovered in the original. In the situation of males, each cell becomes a sperm. In the case of females, one cell becomes one egg and also the other three come to be polar bodies which are not used.

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Meiotic Recombination (Crossing over):

Your parental each have at the very least one pair of alleles (versions of a gene) because that every properties (and numerous pairs that alleles because that each polygenic trait). You finished up with half of mom"s paired genes and fifty percent of dad"s paired genes. However each non-identical-twin kid of these parents end up v a different combination. Imagine, because that example, that eye shade was managed by a solitary gene, and also that mom could have B, the allele because that brown eyes or b, the allele because that blue eyes, and also dad could likewise have B or b. This leads to 4 possibilities: You could get B from mom and also B native dad, or B indigenous mom and b indigenous dad, or b native mom and also B from dad, or b indigenous mom and b from dad. Every sperm and egg will finish up v either B or b from mom and also either B or b native dad. It"s a upper and lower reversal of the coin. However this happens independently for every trait, therefore just since you acquired your dad"s brown eye doesn"t mean you"ll acquire his blond hair too. Each sibling is 50% mom and also 50% dad, yet which 50% that each have the right to vary in the siblings. This shuffling process is well-known as recombination or "crossing over" and also occurs while the chromome pairs are lined up in Metaphase I.