Purpose: Meiosis is a distinct version that cell division that occurs only in the testes and ovaries; the organs that develop the male and female reproductive cells; the sperm and also eggs. Why is this different? plain body cells have a complete set of chromosomes. If human body cells indigenous mom and also dad unify to form a baby, the fertilized egg would have actually twice as plenty of chromosomes together it should. Meiosis is sometimes called "reduction division" because it to reduce the number of chromosomes to half the common number for this reason that, when combination of sperm and also egg occurs, infant will have the exactly number. Because of this the function of meiosis is to develop gametes, the sperm and eggs, with fifty percent of the genetic complement of the parent cells. In the figures below, pink to represent a hereditary contribution from mom and also blue represents a hereditary contribution native dad. In this example, a diploid body cell includes 2n = 4 chromosomes, 2 native mom and also two indigenous dad. In humans, 2n = 46, and also n = 23.

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Meiosis I


Meiosis II

Meiosis I

Interphase I: the same to Interphase in mitosis.

Prophase I: the same to Prophase in mitosis.

Metaphase I: instead of all chromosomes pairing up along the midline the the cell as in mitosis, homologous chromosome pairs line up beside each other. This is referred to as synapsis. Homologous chromosomes save the corresponding alleles donated native mother and also father. This is additionally when meiotic recombination, likewise know together "crossing over" (see below) occurs. This procedure allows for a hereditary shuffling that the characteristics of the 2 parents, producing an practically infinite variety of feasible combinations. See the close-up diagram below.

Anaphase I: rather of chromatids dividing at the centromere, homologous chromosome bag (now shuffled by crossing over) relocate along the spindle fibers to the contrary poles.

Telophase I: The cell pinches and also divides.

Meiosis II

Prophase II: the is visibly apparent that replication has actually not occurred.

Metaphase II: The paired chromosomes heat up.

Anaphase II: The chromatids break-up at the centromere and migrate along the spindle fibers to opposite poles.

Telophase II: The cell pinch in the center and also divide again. The final outcome is four cells, each with fifty percent of the hereditary material uncovered in the original. In the situation of males, every cell becomes a sperm. In the instance of females, one cabinet becomes an egg and also the various other three come to be polar body which room not used.

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Meiotic Recombination (Crossing over):

Your parental each have at least one pair of alleles (versions the a gene) because that every properties (and plenty of pairs that alleles for each polygenic trait). You finished up with half of mom"s paired genes and fifty percent of dad"s paired genes. Yet each non-identical-twin child of these parents ends up v a various combination. Imagine, because that example, the eye color was managed by a solitary gene, and that mom can have B, the allele for brown eyes or b, the allele because that blue eyes, and dad could also have B or b. This leader to 4 possibilities: You might get B from mom and B native dad, or B indigenous mom and b native dad, or b indigenous mom and B indigenous dad, or b indigenous mom and b indigenous dad. Every sperm and also egg will finish up through either B or b indigenous mom and either B or b from dad. It"s a flip of the coin. Yet this happens individually for each trait, for this reason just since you got your dad"s brown eyes doesn"t average you"ll acquire his blond hair too. Every sibling is 50% mom and also 50% dad, but which 50% of each can vary in the siblings. This shuffling process is well-known as recombination or "crossing over" and also occurs while the chromome pairs room lined increase in Metaphase I.