Linkages Flashcards
How many chromosomes do humans have
46 chromosomes
23 pairs
What are 22 pairs of chromosomes
Autosomes
What are the autosomes like for male and female
Both the same (although alleles differ)
What is pair 23
The sex chromosomes X and Y
What is pair 23 of a female like
XX
What is pair 23 of a male like
XY
What is any gene found on theX/Y chromosome
Why
Sex- linked
As the chance of inheriting the gene will be dependent on whether you’re a boy/girl
What chromosome is a sex linked gene mostly found on
Why
The X chromosome
It’s bigger than Y (more alleles) so for most of its length there is no homologous section on the Y
If phenotypes are controlled by recessive alleles on this part of X, they will be more commonly expressed in males as there will be no dominant allele on Y chromosome to compensate
E.g in humans of sex linkage
Haemophilia
What’s haemophilia
Genetic condition that means individuals don’t have proteins needed to make blood clots
What can haemophilia be caused by
A recessive allele on the X chromosome that codes for non-functional protein involved in clotting
Who is haemophilia more common in
Why
Men
Historically women’s wouldn’t survive (periods)
Who can boys and girls only inherit haemophilia from
Why
Their mother
As the defective recessive allele is only found on the X chromosome
How can a mother not express the phenotype but still pass on the genotype to her children
As she may be a carrier of the recessive allele
Another e.g of sex linkage
Colour blindness
Also been linked to recessive allele on the X so is more common in males than females
