A program to help you understand sex-linked inheritance
The Sexlink program will start with a pedigree like the one shown here.
It will include one or more shaded individuals who have a recessive genetic condition,
caused by the X-linked allele a. Your task is to fill in genotypes
to explain all phenotypes in the pedigree.
The allele/chromosome template
The red template box contains X chromosomes with A and a alleles,
plus a Y chromosome. The ? symbol should be used where you cannot predict one or both alleles
of an inherited genotype.
The pedigree has three founder individuals, who have no parents shown.
They are marked here with the letter F. Their genes come from the template box.
The other individuals in the pedigree must inherit their genes from their parents.
The recessive allele is rare
This exercise assumes that we are dealing with a rare recessive condition.
When assigning alleles in the founder individuals, we should therefore try to minimise
the number of copies of the rare a allele.
In fact the pedigrees shown, can all be solved by putting in just ONE such allele.
This is provided to let you change your chosen allele/chromosome. Note that
if an allele has already been passed on to offspring, inherited copies will also be binned at the same time.
Form of the pedigree
Females are shown to the left in a mating. Furthermore the chromosome/allele inherited
from the female parent is always shown as the left of the two chromosomes. Try it out.
To get the best understanding of sex-linked inheritance you should try to run a number of pedigrees.
Please start this exercise by putting chromosomes into the three founder individuals.
There are two founder males in this pedigree, and you should be able to fill in genotypes for them.
With the female there are two possible genotypes,
but because the a allele is rare, you can assume that there won't
be more than one a allele amongst the three founder individuals.
When you have done this, click the "Founders complete?" button