CellBio7 - Meiosis The basis of Mendelian Genetics Mitosis...

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Unformatted text preview: Meiosis The basis of Mendelian Genetics Mitosis = Asexual Reproduction Vegetative Reproduction Results in genetic constancy Offspring = clones of parents Variation by random mutation Rapid and efficient means of reproduction Meiosis = Sexual Reproduction Results in genetic diversity Offspring are not identical to parents or each other 2 parents each contributes 1 gamete to each offspring Asexual reproduction = efficient way to use resources Sexual reproduction requires large expenditure of energy Energy required for mating , Detracts from other useful activities such as feeding and caring for existing offspring. Requires that resources be used to maintain a large population of males that do not bear offspring Genetic variation allows natural selection and evolution Meiosis and Sexual Reproduction - The Cellular Basis of Mendelian Genetics Most eukaryotic organisms have 2 complete sets of genes one set donated by the mother, the second set donated by the father The two chromosomes of a pair contain the same genes The pair are called homologs, or homologous chromosomes Human cells have 23 pairs of chromosomes, 46 total Karyotype of a Human Female, Aligned by Chromosome Size Females have two X chromosomes, males have one X and one Y chromosome Karyotype of a Female, Aligned by Chromosome Size 23 pairs of chromosomes 46 chromosomes 92 chromatids Each chromosome actually has 2 chromatids Meiosis and Sexual Reproduction - The Cellular Basis of Mendelian Genetics Most cells in the body are diploid and contain 2 sets of genes (termed 2 n ) During formation of eggs and sperm, only one set is retained, one set is lost (eggs and sperm are haploid or 1 n ) The process of reducing the number of chromosomes to the haploid state is called meiosis The diploid state (2n) is regained when an egg cell is fertilized by a sperm cell The Basis of Genetic Diversity Asexual Reproduction With asexual reproduction as occurs in bacteria, protists, and certain plants, cells divide by Fssion Each daughter cell receives the exact same genes as the parent Genetic diversity occurs through random mutation The Basis of Genetic Diversity Sexual Reproduction Gene re-assortment occurs during meiosis when the egg cells and sperm cells are produced and when egg cells and sperm cells combine to form the fertilized egg Meiosis In meiosis there are 2 cytoplasmic divisions in a row without an intervening S phase A human diploid cell begins meiosis after DNA synthesis, with 46 chromosomes (92 chromatids) In each Fnal gamete only one homolog of each pair is retained (the haploid state), and each chromosome has only 1 chromatid Meiosis movie http://www.csun.edu/~klb27749/saugus_classes/biology/movies/meiosis.html The frst division is called Meiosis I , the second is called Meiosis II The phases oF Meiosis I and Meiosis II, like the stages oF Mitosis, are called 1) prophase 2) prometaphase 3) metaphase 4) anaphase and 5) telophase but there are important diFFerences between Mitosis and Meiosis Meiosis I...
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CellBio7 - Meiosis The basis of Mendelian Genetics Mitosis...

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