BIO 101 Chromosmal Basis of Heredity.docx

BIO 101 Chromosmal Basis of Heredity.docx - BIO 101...

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BIO 101 Chromosomal Basis of Heredity How do we study Chromosomes? 1. Karyotyping: Examination of metaphase chromosomes. Karyotype Preparation: Stopping the Cycle 1. Cultured cells are arrested at metaphase by adding colchicine. 2. This is when cells are most condensed and easiest to identify. 3. Arrested cells are broken open. 4. Metaphase chromosomes are fixed and stained. 5. Chromosomes are photographed through microscopes. 6. Photograph of chromosomes is “cut up” and arranged to form karyotype diagram. Homologous Chromosomes 1. Homologous autosomes are identical in length, size, shape, and genes contained. 2. Sex chromosomes (X & Y) are not identical but still have regions of homology. 3. Homologous chromosomes recombine with each other, then segregate from one another during meiosis. Sex Chromosomes 1. Discovered in late 1800s. 2. In mammals & fruit flies male is dominant trait. a. XX is female XY is male. 3. In other groups, XX is male, XY is female. 4. In humans, female is the default state. The Y Chromosome 1. Fewer than two dozen genes identified. 2. One is the master gene for male sex determination.
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  • Summer '11
  • Y chromosome, Fragile X syndrome, Turner syndrome

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