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MED1201 (4)


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University of Ottawa
Dr Kingswell

GENETICS TUTORIAL II Monday, September 24, 2012 Slide 2 - pedigree is very common on midterms/exams - hardy-weinberg eq’b question might be there Slide 4 - Another factor NOT included: diploid organism Slide 5 - Examples to look at: Cystic fibrosis - PKU = causes intellectual disability but is treatable - What if there’s more than one gene? – you’d have to use a different equation Slide 7 a) See loose leaf paper b) Autosomal recessive. Risk of having, it’s ¼ c) 2/3 (1/3 is AA, 2/3 is Aa, 1/3 is aa) d) It’s too damn high! But we need numbers! Answer is 1/22. Charles’ chances of being a carrier is ½ (many unaffected kids with Bob and Betty. Betty’s sister’s son + her own daughter have affected child, so she’s likely the carrier. Bob is likely not) For Charles’ wife, we assume the general population. 1/2000 for CF, so q^2 = 1/2000, q = 1/44. p = 1 – q = 43/44 ~1. So 2pq = (2)(1/44)(1) = 1/22. So Debby’s risk is ½*1/22*1/4. ½ is likelihood Charles is a carrier. 1/22 is how likely Charles’ wife is a carrier. ¼ is the likelihood that Debbie will have CF if both are carriers. - Likelihood that Debbie is a carrier = [(1/2)(1/2)(21/22)(1)] + [(1/22)(1/2)(1/2)(1)] + [(1/2)(1/22)(2/3)] e) Barbara, Calvin, Cathy, Betty f) It could be the same family mutation (same nucleotide) Slide 8 - Very likely dominant – autosomal dominant. It’s passed on to every generation - NOT X-LINKED RECESSIVE: not X because a male passed it onto his son - Not Y-linked because an affected male did not pass it on to a son - Disease = testicles don’t descend + urethra doesn’t position properly - THEREFORE – AUTOSOMAL DOMINANT, SEX-LIMITED - IF autosomal dominant – she has 50% chance (father Aa, mother aa) - IF AD sex-limited: she’s female – so she won’t be affected - Expressivity = the degree to which a phenotype is expressed. e.g. neurofibromitosis = kids over time will eventually develop bum
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