meiosis - Web Animation Meiosis After reading the text, you...

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Web Animation Meiosis After reading the text, you should be able t o... Define karyotype. Explain the notation used to describe the number and type of chromosomes pres- ent in an organism or a particular type of cell. Explain what is meant by the term ploidy and give an example of its use. After viewing this animation , you should be able t o... Explain why meiosis is known as a reduction division. Name the phases of meiosis and briefly describe what occurs in each one. Compare and contrast the processes of mitosis and meiosis. NARRATION Chromosome Replication This is a representation of a cell before it begins meiosis, a process in the nucleus that divides the chromosome number in half. For clarity, the nuclear membrane is not shown. Also, the chromosomes are depicted as condensed, although during interphase of the nor- mal cell cycle, they are actually thin and dispersed and not visible under a light micro- scope. Before a cell enters meiosis, it first replicates its DNA. After DNA replication, the chromo- somes are duplicated so that each has two identical sister chromatids connected at a struc- ture called the centromere. Meiosis I Meiosis consists of two successive cell divisions called meiosis I and meiosis II, each of which is subdivided into four phases. In the first phase of meiosis I, called prophase I, the homologous chromosomes (or homologs) in a diploid cell come together in a process called synapsis. The synapsed pairs are known as tetrads. Each tetrad consists of one chro- mosome inherited from the mother (colored red in the diagram) and one inherited from the father (colored blue).
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Where they are synapsed, the chromosomes can cross over each other, forming an X- shaped structure called a chiasma. At the crossover sites, the homologous chromosomes exchange segments. This exchange results in genetic variability in the daughter cells. The second major phase of meiosis I is
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This note was uploaded on 12/11/2011 for the course BIO 152 taught by Professor Cordon during the Spring '07 term at University of Toronto- Toronto.

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meiosis - Web Animation Meiosis After reading the text, you...

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