Sex-Linkage Flashcards
What are the sex chromosomes for males and females
Male - XY
Female - XX
How many chromosomes do humans have
46
23 pairs
What gametes do males and females produce
As females have two X chromosomes, all the gametes are the same in that they contain a single X chromosome
As males have one X chromosome and one Y chromosome, they produce two different types of gamete - half an X chromosome and half a Y chromosome
What is a sex linked gene
Any gene that is carried on either the X or Y chromosome
The X chromosome is much longer then the Y chromosome. What does this mean for males
That for most of the length of the X chromosome, there is no equivalent homologous portion of the Y chromosome. So therefore characteristics that are controlled by the recessive alleles on this non homologous portion of the X chromosome will appear more frequently in males
Why will the recessive allele appears more frequently in males
As there is no homologous portion of the Y chromosome that might have the dominant allele, in the presence of which the recessive allele does not express itself
What is an X linked genetic disorder
It’s a disorder caused by a defective gene on the X chromosome
How does a male inherit haemophilia from a carrier female
As males only obtain their Y chromosome from their father, it follow that their X chromosome comes from their mother. As the defective alleles that does not code for the clotting protein is linked the X chromosome, males always inherit the disease from their mother. If their mother does not suffer from the disease she may be heterozygous and just be a carrier. So therefore she produces one dominant allele that doesn’t lead to the disease and carries the other
Why can males not pass the disease to a son but can to a daughter
As males pass the Y chromosome to their son. But they can pass the disease via there X chromosome to their daughter, who would then become a carrier
