lecture31

lecture31 - Lecture 31: Genetic Heterogeneity and Complex...

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Lecture 31: Genetic Heterogeneity and Complex Traits • Allelic heterogeneity • Nonallelic heterogeneity • r • Twin studies • Sib-pair analysis
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Each of the heritable human traits that we have discussed in recent weeks is monogenic Each of these traits was quite straightforward from a Mendelian perspective: invariably caused by mutation in the same gene. Sickle cell disease: autosomal recessive Phenylketonuria: autosomal recessive Huntington's disease: autosomal dominant genetic homogeneity all affected individuals have the same mutation in the same gene
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ALLELIC HETEROGENEITY cystic fibrosis (CF): • autosomal recessive disorder affecting 1/2500 newborns in populations of European origin • phenotype: sticky viscous secretions obstruction of pancreas and airways pancreatic insufficiency (treated with enzyme supplements) + lung infections • mapped to chromosome 7 by genetic linkage analysis in 1985 • gene identified at molecular level in 1989: encodes a chloride channel protein allelic heterogeneity Would such allelic heterogeneity affect the outcome of combining LOD scores from multiple families with affected children? No, because all such families would show linkage to the same chromosomal locus. • > 600 mutant alleles in the gene have been identified
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DUCHEYNNE BECKER TWO MUSCULAR DYSTROPHIES
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retinitis pigmentosa (RP): • degeneration of retina (accompanied by deposits of pigment in retina) progressive visual impairment blindness • population prevalence of 1/3,000 • one of most common causes of blindness among middle aged in developed countries • autosomal recessive inheritance in 84% of affected families • autosomal dominant inheritance in 10% of affected families • X-linked recessive inheritance in 6% of affected families • At least 66 different genetic loci implicated but RP appears to be result of a single gene mutation in any given family, at least in most cases NON-ALLELIC HETEROGENEITY
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lecture31 - Lecture 31: Genetic Heterogeneity and Complex...

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