Meiosislect - Meiosis and Sexual Reproduction Meiosis"to...

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Meiosis and Sexual Reproduction
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Meiosis - “to make smaller” Special type of cell division Used only for sexual reproduction Halves the chromosome number prior to fertilization (2n -> n) Parents diploid (2n) Meiosis produces haploid (n) gametes Gametes fuse in gertiliztion to form diploid zygote N (egg) + n (sperm) -> 2n zygote Becomes the next diploid generation
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Meiosis In diploid body cells chromosomes occur in pairs Humans have 23 different types of chromosomes Diploid cells have two of each type Chromosomes of the same type are said to be Homologous chromosomes (Homologues) They have the same length Their cnetromeres are positioned in the same place One came from the father (the paternal homolog) the other from the mother (the maternal homolog) When stained, they show similar banding patterns Because they have genes controlling th same traits at the same positions
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Homologous Chromosomes Human Karyotype Identified based on: 1) appearance 2) length 3) centromere position Alleles = alternate forms of a gene Homozygous Heterozygous Humans 22 pairs autosomes 1 pair sex chromosomes female: XX male: XY
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Homologous Chromosomes Homologous chromosomes have genes controlling the same trait at the same position Many genes exist in several variant forms in a large population Homologous copies of a gene may encode identical or differing genetic information The variants that exist for a gene are called alleles
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Mitosis Mitosis 46 46 46 46 Human Meiosis Meiosis 46 46 23 23 23 23 23 23 n + n zygote Egg Sperm 2n Unduplicated chromosomes Duplicated chromosomes Unduplicated chromosomes Unduplicated chromosomes Duplicated chromosomes Meiosis 1 reduction division Meiosis II equatorial division Gametes Spores
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Meiosislect - Meiosis and Sexual Reproduction Meiosis"to...

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