caption: 8.13 Meiosis reduces the chromosome number from diploid to haploid
exif: {"Image DocumentName": "8.13 Meiosis reduces the chromosome number from diploid to haploid", "Image ImageDescription": "Like mitosis, meiosis is preceded by interphase. Chromosomes duplicate during the S phase. Unlike mitosis, meiosis has two divisions. During meiosis I, homologous chromosomes separate. The chromosome number is reduced by half. During meiosis II, sister chromatids separate. The chromosome number remains the same. Student Misconceptions and Concerns. 1. Students might not immediately see the need for meiosis in sexual reproduction. Consider an example of what would happen over many generations if gametes were produced by mitosis. The resulting genetic doubling is prevented if each gamete has only half the genetic material of the adult cells. 2. How meiosis results in four haploid cells, yet mitosis yields two diploid cells, is often memorized but seldom understood. It can be explained like this. Consider a pair of chromosomes in a cell before any cell divisions. This pair of chromosomes duplicates such that two chromosomes become four (although each pair of sister chromatids are joined at their centromeres). Therefore, mitosis and meiosis each typically begin with four chromosomes. Mitosis divides once, producing two cells, each with two chromosomes. Meiosis divides twice, sorting the four chromosomes into four separate cells. Teaching Tips. 1. In meiosis I and meiosis II, the processes begin with duplicated pairs of chromosomes. This pair becomes two pairs. The two pairs include four items. Sort this group into two subgroups, and you are back to two pairs. Divide again, and you have separated four items into four groups of one. This can work with the shoe analogy if you wish to continue the reference. A pair of shoes is reproduced and becomes two pairs. Mitosis sorts them back into two pairs of shoes. However, meiosis keeps sorting, eventually isolating each shoe. Each solitary shoe would then represent a gamete, which would then be matched with another similar shoe (gamete) to make a new pair of shoes (organism). Copyright \u00a9 2009 Pearson Education, Inc.", "Image XResolution": "300", "Image YResolution": "300", "Image ResolutionUnit": "Pixels/Inch", "Image Software": "SlidePlayer", "Image YCbCrPositioning": "Centered"}