Lect2 - MitosisandMeiosis Traits are controlled by genes...

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1 Mitosis and Meiosis Traits are controlled by genes Each individual contains two copies of a gene. Gene segregation Each individual has thousands of genes Independent assortment What is the biological basis for Mendel’s laws? green x yellow yellow x yellow yellow: yellow:yellow:green
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2 Genes reside on Chromosomes Genes reside on chromosomes, understanding the behavior and inheritance patterns of individual genes requires an understanding of the behavior of inheritance patterns of chromosomes. The processes of mitosis and meiosis describe the two basic patterns of chromosome behavior in higher eukaryotes Mitosis: a form of cell division that produces two daughter cells of identical genotypes Meiosis: a form of cell division in a diploid cell that produces four haploid cells Meiosis only occurs in a small specialized set of cells known as the germ cells.
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3 Development Meiosis 2N ---->4N ---->N+N+N+N Mitosis 2N ---->4N ----> 2N+2N 2N  | 4N    |  | N  |  |  | 2N  |  | 4N  |  | 2N
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4 The Mitotic cell cycle The mitotic cycle alternates between the replication of each chromosome (S phase) and the  segregation of the replicated chromosomes to two daughter nuclei (M phase).  The intervals between these phases are known as gap phases and this divides the cell cycle  into four phases M, G1, S and G2. Interphase consists of G1, S, and G2.
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5 Chromosome number Smallest number: The female of a subspecies of the ant, Myrmecia pilosula, has one pair of chromosomes per cell. Its male has only one chromosome in each cell. Largest number: In the fern family of plants, the species Ophioglossum reticulatum has about 630 pairs of chromosomes, or 1260 chromosomes per cell. Species Haploid number (n) Human 23 Monkey 21 Mouse 20 Frog 13 Fruit fly 4 C. Elegans 6 Corn 10 S. Cerevisiae 16 S. Pombe 3 Indian muntjack 3 n=2 Homologous Chromosomes (99.99% similar) Haploids are 1N Diploids are 2N Tetraploids are 4N
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6 Mitosis Mitosis is the period in which the chromosomes condense align along the metaphase plate and migrate to opposite poles. In part because this is the most visibly dramatic stage in the cell cycle much research has focused on these mitotic events. Net result: The creation of two daughter cells with identical chromosome complements.
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7 Replication of DNA  Each DNA mol is a chromatid The two chromatids attached to the  centromere are called sister chromatids Homologous  Chromosomes 99.99% identical Mitosis n=2 2N n=2 4N
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8 Mitosis Sister chromatids line up at the  metaphase plate. Sister chromatids separate to opposite  poles n=2 4N n=2 2N
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9 Mitosis in haploid and diploid Replication of DNA  A a A A a a n=1 2N n=1 4N A a A a n=1 2N Replication of DNA  A A A n=1 1N n=1 2N A A n=1 1N
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10 Cell cycle and cancer Currently the cell cycle/mitosis is an intensively investigated area of research. This is primarily due to the fact that: 1. The structural and regulatory components governing the cell
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Lect2 - MitosisandMeiosis Traits are controlled by genes...

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