Chapter 12 Meiosis

O metaphase ii replicated chromosomes consisting of

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o Metaphase II- Replicated chromosomes, consisting of two sister chromatids, are lined up at the metaphase plate. o Anaphase II- Sister chromatids separate. The unreplicated chromosomes that result being moving to opposite sides of the cell. o Telophase II- Chromosomes finish moving to opposite sides of the cell. A nuclear envelope forms around each haploid set of chromosomes. When meiosis II is complete, each cell divides to form two daughter cells. Meiosis II occurs in both daughter cells of meiosis I, therefore there are a total of four daughter fells form each original, parent cell. Essentially, in meiosis, one diploid cell with replicated chromosomes gives rise to four haploid cells with unreplicated chromosomes. A Closer Look at Prophase I Step 1: After chromosome replication is complete, sister chromatids stay tightly joined along their entire length. Step 2: When homologs synapse, two pairs of non-sister chromatids are brought close together and are held there by a network of proteins called the synaptonemal complex. Step 3: Crossing over occurs when a complex of proteins cutes the chromosomes and then reattaches the pieces so that segments are swapped between adjacent homologs. The Consequences of Meiosis
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Changes in chromosomal configuration occur only during sexual reproduction- not during asexual reproduction. Asexual Reproduction refers to a mechanism of producing offspring that does not involve the fusion of gametes, and is usually based on mitosis. Sexual Reproduction refers to the production of offspring through the fusion of gametes. Chromosomes and Heredity The changes in chromosomes produced by meiosis and fertilization are significant because chromosomes contain the cell's hereditary material. Chromosomes contain the instructions for specifying what a particular trait might be in an individual. The offspring of asexual reproduction are clones of their parent. Two aspects of meiosis that create variation among chromosomes: 1. Separation and distribution of homologous chromosomes 2. Crossing over, and then ask how these processes interact with fertilization to produce genetically variable offspring. Independent Assortment Produces Genetic Variation Each somatic cell in your body contains 23 homologous pairs of chromosomes and 46 chromosomes in total. When pairs of homologous chromosomes line up during meiosis I and the homologs separate, a variety of combinations of maternal and paternal chromosomes can result. Each daughter cell gets a random assortment of maternal and paternal chromosomes. The Role of Crossing Over Crossing over produces new combinations of alleles within a chromosome- combinations that did not exist in either parent. This phenomenon is known as recombination. Genetic recombination is any change in the combination of alleles on a given chromosome.
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