Inheritance of Sex-linked Characteristics Flashcards
Where is the genetic information for gender carried?
On 2 sex chromosomes.
Female chromosomes (mammals)
XX.
Male chromosomes (mammals)
XY.
What is the probability of parents having a boy and girl?
50%.
On a genetic diagram how are the gametes presented?
In a circle.
What does it mean when it says some characteristics are sex-linked?
Alleles that code for that characteristic are found on sex chromosomes.
What does the term X-linked genes mean?
Because the X chromosome is larger than the Y chromosome it carries more genes. So most genes on sec chromosomes are carried on the X chromosome.
Why do males show more recessive phenotypes?
Because they only have one X chromosome meaning they often only have one allele for a sex-linked gene.
This means even if they have one copy, they express this characteristic even if its recessive - they are more likely to have more recessive phenotype sex-linked genes than females.
Where are genetic disorders caused by faulty alleles located?
Sex chromosomes.
Examples include colout blindness and haemophilia.
Where are the faulty alleles for colour blindness located?
On the X chromosome.
They are called X-linked disorders.
(Y-liked disorders do occur, but less common)
EXAMPLE
For colour blindness what is the chromosome and allele represented by?
Xn (Capital X and small lower case n)
EXAMPLE.
What happens to the Y chromosome for colour blindness?
It doesn’t have an allele for colour vision so its just represented as Y.
EXAMPLE.
For a women to be colour blind, what does she need to have? What about men?
Women need 2 copies of the recessive allele to be colour blind.
Men only need 1 copy to be colour blind.
(colour blindness is more common in men)
EXAMPLE.
What happens if women have 1 copy of the recessive allele?
They are said to be carriers.
What is a carrier?
A person carries an allele which isn’t expressed in the phenotype, it can be passed on to offspring.
