Biology 1202B Lecture Notes - Lecture 18: Advanced Maternal Age, Aneuploidy, Genetic Counseling
21 Mar 2017
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Aneuploidy and disease: only 3 autosomal trisomies survival postnatal, 21, 18 and 13, fall below gene density, the phenotype of a trisomy depends on the genes on the extra chromosome. Less genes means less phenotypic effect: chromosme 21 is the most tolerable, viable, because of its size, 18 has less genes, chromosome with few genes may be tolerated, monosomies = lethal. Aneuploidy is due to meiotic nondisjunction: failure of a pair of chromosomes to disjoin during one of the meiotic divisions, different outcomes when the nondisjunction is in meiosis i or ii. Inversion - depends on location of breakpoint relative to genes/ regulatory sequences. Virtual clicker question: what happens to homologous chromosomes during meiosis when one has a large inversion, they pair as normal, ignoring the inverted region, an alternate structure is formed * Loop formed by inverted chromosome pairing with homolog in meiosis i: cross over event may occur in loop.
