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Lecture 15

BIOL 207 (10/18/13) Lecture 15 and 16: Human Pedigree Analysis - Part 1 and 2

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Biology (Biological Sciences)
Mike Harrington

BIOL 207 (October 18, 2013) Lecture 15: Human Pedigree – Part 1 (con’t)  I-Clicker Question: A husband and wife both have achondroplasia. What is the probability that their first child will also have this condition? o Answer: 0.67 o Why not 0.5?? Because we are assuming that this child is viable. Being homozygous for the mutant AND dominant allele results in non-viable offspring. Diagram below: Representative XR Pedigree Chart  If father is affected: o Sons will not be affected o Daughters will be carriers  If mother is a carrier: o Sons may or may not be affected o Daughters may or may not be carriers  Example: Hemophilia A o F8 gene @ Xq28 encodes for a blood clotting factor (called VIIIC)  A mutation on this gene results in inability for body to clot blood.  Internal and external bleeding will not stop! o There is a recombinant human factor VIIIC on the market that allows for blood coagulation.  Life expectancy of people with hemophila increased from 1.5 years to 65 years (19002000) because of this. o Mutation is recessive because the heterozygous genotype in females still allows for “generally” normal blood coagulation (maybe easy to bruise, takes a while for cuts to stop bleeding) X-Linked Dominant  A = mutant allele  a = WT allele A  X /Y = affected male  X /X and X /X = affected females  Affected father? o Sons are unaffected o Daughters are affected  Affected Mother o Sons may or may not be affected o Daughters may or may not be affected  Example: Fragile X Syndrome (aka FMR = fragile mental retardation) o FMR1 gene @ Xq27 (no need to remember gene names and locations for exams as they will be provided)  Encodes for a protein needed for neuron development  FMR1 (WT allele)  (CGG) nases are repeated < 200 times -  FMR1 (mutant allele
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