Sex-linked Inheritance Flashcards
What are ‘sex-linked’ genes?
Where certain genes are carried on one of the sex chromosomes instead of the normal autosomal chromosomes, in humans - carried on the x chromosome.
What happens when ‘sex-linked’ genes occur?
Means that some conditions occur more in one sex.
What are 3 examples of ‘sex-linked’ conditions?
- Haemophilia.
- Red-green colour blindness.
- DMD.
How would you spot a condition is ‘sex-linked’?
When many offspring are studied, a condition will occur much more often in one sex than the other. Such patterns show up when studying family trees and pedigree charts.
What term is used to describe the sex genes of a female? Definition?
Homogametic sex: females produces all the same gametes, xx.
What term is used to describe the sex genes of a male? Definition?
Heterogametic sex: males have two types of gametes, x and y.
What gamete is the gene for haemophilia carried on? Recessive or dominant?
The haemophilia is carried on the x chromosome and is recessive so needs both alleles present to be expressed.
Why can haemophilia occur mostly in males?
Because the gene for haemophilia is carried on the x chromosome and is recessive so needs two alleles present to be expressed but males only have one x chromosome so only needs the one allele present but females needs both present.
How can females be carriers of haemophilia?
If they have one faulty allele and one normal allele, then can pass on the faulty allele to their offspring.
Why can a man with haemophilia not pass this condition onto his son?
A man passes a y chromosome onto his son as mum has no y chromosome so must pass on the x chromosome so will not get the faulty gene.
What does it mean when 2 alleles are ‘co-dominant’?
Both of the alleles have the same power to be expressed so compromise with one another, for example, if a white and red allele are co-dominant and present, the offspring will be pink.
In a question, fur colour gene is carried on the x chromosome, the allele for ginger fur and black fur are co-dominant so produce a tortoiseshell offspring, why can a male cat not have tortoiseshell fur?
Because they only have one x chromosome and as the gene for fur colour is carried on the x chromosome, the cat will either be ginger or black as cannot carry both of these alleles.
What is ‘dihybrid inheritance’? Example?
Inheritance involving 2 traits, for example, height and colour.
What would an example for a genotype be in dihybrid inheritance? Gametes?
RrBb:
- Gametes: RB, Rb, rB, rb.
How can we use pedigree charts in inheritance?
Helps us identify genes being passed on throughout the family.
