Cell and Inheritance Ch. 4, section 3

Walter Sutton An American geneticist Wanted to understand how sex cells (sperm and egg) form. Chromosome Theory! Genes are carried from parents to offspring on chromosomes.

Chromosome Pairs Sutton observed that when a sperm and an egg join together in fertilization they formed 24 chromosomes. (in grasshoppers) That meant that there were 12 pairs. The offspring received one chromosome from each parent. People have 46 chromosomes or 23 pairs.

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Meiosis Before Meiosis: chromosomes replicate Meiosis 1: a.Chromosome pairs line up in the center. b. pairs separate  opposite ends of cell. c.Two cells form, each with half the number of chromosomes.

Meiosis 2 a.Chromosomes with their two chromatids move to the center of the cell. b.Centromeres split, and single chromatids separate. Then move to opposite ends of the cell.

End of Meiosis 4 sex cells have been produced. Each cell has ½ the number of chromosomes the parent cell had at the beginning. Only contains 1 chromosome pair.

Meiosis During meiosis, a cell produces sex cells with half the number of chromosomes. The chromosome pairs separate and are distributed to two different cells. The resulting sex cell has only half as many chromosomes as the other cells in the body.