*The gene is NOT on a sex chromosome, but SEX affects the phenotype

*Example-baldness-dominant in males, recessive in women

*If ‘B’ represents bald and ‘b’ is hairy then

Men must be bb to keep hair

Women can be Bb or bb to keep hair

*Caused by a gene that is located on a SEX chromosome (X or Y)

*Most sex-linked traits are found on the X chromosome

*Is the pedigree beside this like MOST sex-linked traits?

*Most are recessive*Examples-hemophilia, red-green colorblindness

*Males are more likely to have these because they cannot be carriers

*Why?

*Males are XY-if their ‘X’ has a bad gene, there is nothing on the ‘Y’ to dominate over it

*N

n

* XNXN=Normal *XNXn=CARRIER, but IS

NOT colorblind

*XNY=Normal

*XnY=HAS red-green colorblindess

*Carrier mom XNXn

*Normal Dad XNY

XN Xn

XN XNXN XNXn

Y XNY XnY

*Orange and Black Alleles are on the X chromosome in cats

*White is on another chromosome (autosome).

*Result-some cells make black fur, some orange

*Polygenic-more than one pair of alleles determines phenotype--eye color

*Female genotype?

*Male genotype?

*What percent of possible offspring are female?

*What percent of possible offspring are male?

What is the genotype of a woman who is a carrier of hemophilia?

What is the genotype of a man who does not have hemophilia?

Will any of their children potentially have hemophilia?

What sex will the child have to be?

Last vocabulary term of importance.

Purebred – Always breeds true to dominant trait. i.e. homozygous dominant individual