Biology - Inheritance of X-linked recessive characteristics
Inheritance of X-linked recessive characteristics
* A father with the characteristic cannot pass the defective allele (on
an X chromosome) to his sons as he only passes on the Y chromosome to sons
* More males than females are likely to show the characteristic (a female
needs two X chromosomes with the defective allele for her to show the
condition; a male only needs one)
* A carrier female (heterozygous for that allele) does not show
the characteristic but may pass the allele concerned to some of her sons
who will therefore show the characteristic. Sons get their X chromosome
from their mother.
If a characteristic or trait is passed down only from father to sons and
never to daughters, then the characteristic shows a Y-linked pattern of
inheritance, for example, hairy ears in males. The inheritance pattern in a
family could differ from that expected because of random mutations.
Sometimes individuals in a family are adopted and this can complicate
interpretation of pedigrees if the adoption is not known by the individual
concerned.
Practise working out inheritance patterns for a variety of pedigrees. Next
to each individual in the pedigree, write the symbols for the genotype.
Work from the known genotype to the unknown.
