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.
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
Life expectancy of people with hemophila increased from 1.5 years to 65
years (19002000) 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)
A = mutant allele
a = WT allele
X /Y = affected male
X /X and X /X = affected females
o Sons are unaffected
o Daughters are affected
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