Sex linkage

what is a sex linked gene

a gene located on a sex chromosomes (X or Y)

which chromosome is longer

X

characteristics controlled by recessive allele on non-homologous portion of X chromosome will appear more frequently in…

males

why is this?

there is no homologous portion on the Y chromosome that might have the dominant alelle

haemophilia

• slow blood clotting

• internal bleeding

what is the cause of haemophilia

• recessive allele with an altered base sequence that codes for a faulty protein, that can not function and clot blood.

why is there no allele on Y chromosome?

does not carry gene for producing blood clotting protein

males inherit disease from their

mother

heterozygous mother means she is a

carrier

what can be used to trace the inheritance of sex linked characters ?

pedigree chart

features of a pedigree chart

• circle for females

• square for males

• shading to indicate characters