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

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