Why are males affected by recessive sex-linked traits more often than females?

Answer 1

Males more frequently express sex-linked traits because they only have one X chromosome. Since most of the genes on the sex chromosomes are on the X chromosome and very few are on the Y, so any recessive gene on the X chromosome will be expressed.

Answer 2

a male's chromosomes are XY, whereas a girls are XX. With a female, hes sex-linked traits can be dominated by her other X chromosome. Whereas with boys, their Y is what they get, there's no changing it.

Answer 3

Males have only one X chromosome, so a recessive X-linked trait will be displayed in the phenotype [visible on the outside]. Females have two X chromosomes, so both of the chromosomes must have the trait for it to be displayed on the phenotype.

Answer 4

{ Short Answer } - Because females have only one X chromosome.

Males are more likely than females to have sex-linked traits controlled by a recessive allele because they only need one recessive allele to have the sex-linked trait. In contrast, females need two recessive alleles to have the sex-linked trait, so they have a lower probability of having it.

This is best viewed with a Punnet square. Say the recessive allele that controls the sex-linked trait is Xa. XA is the dominant allele and Y is the male chromosome.

Scenario #1

If the mom is XA XA and marries a man with the sex-linked trait Xa Y, then none of the sons will have the sex-linked trait. All the daughters will have the mutant allele, but they will all be carriers with normal phenotypes since they only have one mutant allele.

Xa

Y

XA

XA Xa

Xa Y

XA

XA Xa

Xa Y

Scenario #2

If the mom is XA Xa and marries a man with the sex-linked trait Xa Y, then there is a 50% chance that each child will have the sex-linked trait, regardless of sex.

Xa

Y

XA

XA Xa

XA Y

Xa

Xa Xa

Xa Y

Scenario #3

If the mom is a carrier XA Xa and marries a normal man XA Y, then there is a 50% chance each son will have the sex-linked trait. The daughters may be carriers, but none of them will have the sex-linked trait.

XA

Y

XA

XA XA

XA Y

Xa

XA Xa

Xa Y

Scenario #4

If the mom has the sex-linked trait Xa Xa and marries a normal man XA Y, then all of the sons will have the sex-linked trait. The daughters will be carriers, but none of them will have the sex-linked trait.

XA

Y

Xa

XA Xa

Xa Y

Xa

XA Xa

Xa Y

Scenario #5

If the mom has the sex-linked trait Xa Xa and marries a man who also has the sex-linked trait Xa Y, then all of their children will have the sex-linked trait.

Xa

Y

Xa

Xa Xa

Xa Y

Xa

Xa Xa

Xa Y

As you can see, there are many more strikethrough outcomes (8) where the male has the sex-linked trait controlled by a recessive allele than bold outcomes (3) where the female has the sex-linked trait. Thus, males are more likely than females to have sex-linked traits controlled by a recessive allele.

Answer 5

Females have two X chromosomes, whereas males only have one.

This means that if a female has one normal allele and one affected allele, the trait will not be expressed (because it is recessive, the normal trait will be expressed instead).

However, because males only have one X chromosome, if they have the affected trait, there is no normal trait on the other chromosome to cancel it out - so the trait will be expressed.

Answer 6

Because in heterozygous conditions the female is XX, which offers statistical protection against a recessive condition traveling with the X chromosome. Males, being XY, have no such protection against receiving a recessive allele on the X chromosome.

Answer 7

Because they olny have one X chromosome.