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Human Biology
Course Code
Stephen Wright

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LECTURE 4: Mendelian traits in humans and human pedigree analysis
Mendels laws of inheritance, how applied to DNA level, dominance applied to DNA to
TODAYhow Mendels laws apply to humans, how inheritance in humans studied via
Drosophila cannot self-fertilize simply cross siblings for a number of generations
longer until homozygotes achieved
Using models to understand biology
Mammalian not as fast generation time as Drosophila or elegans, but closer to humans in
Cannot self-fertilize mice can look at large numbers of offspring
Humans are poor genetic organisms cannot do controlled crosses by deciding breeding
couples; not many offspring;
If two offspring, cannot determine 3:1 ratio
Cannot self-fertilize
Using model organisms to understand humans
oForward genetics start with phenotype and tyring to understand at
DNA level
Often involves analyzing mutant phenotypes
Follow pedigrees
oFew progeny too few to look at ratios, so focus on patterns instead
oDeceased not genetically relevant really
Parents not affected
Children do
Parents must have allele but not expressed therefore recessive
Diseased offspring is aa
Parents are Aa
The non-diseased offspring A- meaning it is unknown whether Aa
or AA
No need to worry about ratios
With small sample, easy to get departure from expected ratios
Why is one dominant over the other? They follow Mendelian traits
Autosomal diseases are rarely dominant so if severe effects, expressed immediately and
thus eliminated from the population recessive disease are fewer?
Post-reproduction typically when dominant diseases surface
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