sex-linked traits
Sex chromosomes carry genes that code for traits other than gender.
Traits determined by genes on the X chromosome are called sex-linked traits.
(hemophilia and colour blindness)
A male has XY homologous chromosomes for sex determination.
A female has XX homologous chromosomes for sex determination.
• Receives sex-linked chromosome from mother (give the X)• Phenotype will show sex-linked gene because no other allele to mask it.
xy
• Can inherit sex-linked traits from either parent. • Must have two sex-linked alleles to
show recessive trait.• If receives one recessive sex-linked
allele, she will not show the trait, but she is a carrier.
xx
Father = XY
Mother = XX
XYXX
X
X
X
X
Y
Y
X
X
½ disorder free – 50%
¼ color-blind male – 25%
¼ female carrier – 25%
A pedigree is a diagram representing the phenotype history of a family.
Genotypes can be determined by analyzing the pedigree.
Symbols:Male – squareFemale – circle Dominant trait – blankRecessive trait – filled
A widow's peak hairline (W) is dominant over a straight hairline (w):
ww
W
ww ww ww
wwW W
W
W
WW
w
w
w w
w
?
?