Sex-linked traits are carried on the X or Y chromosome and therefore tend to be inherited by one sex more than the other.

Males are more likely than females to have red-green color blindness or hemophilia, for example, because the allele for each is recessive and located on the X chromosome (X-linked).

Females have two X chromosomes. If a female inherits the recessive color-blindness allele (c) on one X chromosome,

there is still a good chance that her other X chromosome will carry a dominant allele (C) for normal color vision.

Males, on the other hand, have only one X chromosome and normally express any allele found there (fig. 4.20). Ironically, even though color blindness is far more common among males, it can be inherited only from their mothers.

Why? Because only the mother contributes an X chromosome. If a male child inherits c on his mother's X chromosome, he will be color-blind. He has no "second chance" to inherit a normal allele on a second X chromosome.

A female would have to inherit it from both parents in order for her to have a trait such as red-green color blindness.

That happens, but is relatively rare.

The X chromosome carries about 900 genes, most of which have nothing to do with determining an individual's sex.

There are so few functional genes (55) on the Y chromosome-concerned mainly with development of the testes-that all proven sex-linked traits are associated with the X chromosome.

Even though males don't inherit an X chromosome from their fathers, it is possible-indeed not uncommon-for them to inherit some genes from the father's X chromosome.

This happens because, in the male parent, X and Y chromosomes often exchange a few genes in the pseudoautosomal regions at their tips

. Conversely, in rare cases, a daughter can inherit her father's male-determining SRY gene because it has transferred to the X chromosome he passes on to her. Thus, an XY male could inherit a Y chromosome without that “male-determining” gene,

and an XX female could inherit an X chromosome with the "male- determining" SRY gene. This is one reason why a person's gender isn't always rigidly determined by inheritance of an X versus a Y chromosome.

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Question	Answer
Sex-linked traits are carried on the X or Y chromosome and therefore tend to be inherited by one sex more than the other.	Males are more likely than females to have red-green color blindness or hemophilia, for example, because the allele for each is recessive and located on the X chromosome (X-linked).
Females have two X chromosomes. If a female inherits the recessive color-blindness allele (c) on one X chromosome,	there is still a good chance that her other X chromosome will carry a dominant allele (C) for normal color vision.
Males, on the other hand, have only one X chromosome and normally express any allele found there (fig. 4.20). Ironically, even though color blindness is far more common among males, it can be inherited only from their mothers.	Why? Because only the mother contributes an X chromosome. If a male child inherits c on his mother's X chromosome, he will be color-blind. He has no "second chance" to inherit a normal allele on a second X chromosome.
A female would have to inherit it from both parents in order for her to have a trait such as red-green color blindness.	That happens, but is relatively rare.
The X chromosome carries about 900 genes, most of which have nothing to do with determining an individual's sex.	There are so few functional genes (55) on the Y chromosome-concerned mainly with development of the testes-that all proven sex-linked traits are associated with the X chromosome.
Even though males don't inherit an X chromosome from their fathers, it is possible-indeed not uncommon-for them to inherit some genes from the father's X chromosome.	This happens because, in the male parent, X and Y chromosomes often exchange a few genes in the pseudoautosomal regions at their tips
. Conversely, in rare cases, a daughter can inherit her father's male-determining SRY gene because it has transferred to the X chromosome he passes on to her. Thus, an XY male could inherit a Y chromosome without that “male-determining” gene,	and an XX female could inherit an X chromosome with the "male- determining" SRY gene. This is one reason why a person's gender isn't always rigidly determined by inheritance of an X versus a Y chromosome.

Created by: Russells3709

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