Genetics problems X - Linked Inheritance
For a certain set of alleles males receive only one allele, not two. This is because males receive an X
and a Y chromosome, (not homologs) while females always receive two X’s. The X, being much
larger than the Y carries extra genes. Females will always receive two copies of each gene, while
males only receive one.
1)
In humans hemophilia (bleeders disease), is due to a recessive X linked allele. The normal
condition (your blood clots) is due to the dominant allele. Show the phenotypic ratios possible
in a cross between a heterozygous normal female and a normal male.
2)
For hemophilia show the phenotypic ratios possible in a cross between a homozygous normal
female and a hemophiliac male.
3)
In humans normal color vision is due to a dominant allele. Red-green color deficiency is due to
its recessive allele. Show the phenotypic ratios for the following crosses.
A) Homozygous normal female x color deficient male.
B) Heterozygous normal female x color deficient male.
C) Heterozygous normal female x normal male.
D) Color deficient female x normal male.
4)
In humans pseudohypertrophic muscular dystrophy is a condition in which the muscles
gradually waste away, ending in the death of the individual in their early teens. In some
families it has been shown that this condition is due to recessive X linked inheritance. This
type of muscular dystrophy has been observed in males but there has never been a recorded
case in females. Explain
5)
Explain why the allele for pseudohypertrophic muscular dystrophy does not become eliminated
from the human population, even though all males who exhibit this condition die before
reaching sexual maturity?