Start One to one sex chart no email

One to one sex chart no email

In ZW sex-determination system used by birds the opposite is true: the male is the homogametic sex (ZZ), and the female is heterogametic (ZW).

For example, an X-linked recessive allele in humans causes haemophilia, which is much more common in males than females because they are hemizygous (see zygosity) and therefore express the trait when they inherit one mutant allele.

In contrast, a female must inherit two mutant alleles, a less frequent event since the mutant allele is rare in the population.

All offspring of a carrier female have a 25% chance of inheriting the mutation if the father does not carry the recessive allele.

All female children of an affected father will be carriers (assuming the mother is not affected or a carrier), as daughters possess their father's X-chromosome.

Females possessing one X-linked recessive mutation are considered carriers and will generally not manifest clinical symptoms of the disorder.

All males possessing an X-linked recessive mutation will be affected, since males have only a single X-chromosome and therefore have only one copy of X-linked genes.

The incidence of recessive X-linked phenotypes in females is the square of that in males (squaring a proportion less than one gives an outcome closer to 0 than the original).

If 1 in 20 males in a human population are red-green color blind, then 1 in 400 females in the population are expected to be color-blind ().

If the mother is not a carrier, no male children of an affected father will be affected, as males only inherit their father's Y-chromosome. They may be caused by genes on either autosomal or sex chromosomes.

Even in a homozygous dominant or recessive female the condition may not be expressed fully. Examples: female sterility in Drosophila; and many polymorphic characters in insects, especially in relation to mimicry.

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