Humans have 46 chromosomes in every cell 2 of these chromosomes make us male or female Female XX Male XY The Sex Chromosomes Has information for male traits Few other genes The Y chromosome ID: 242590
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Slide1
Sex-Linked TraitsSlide2
Humans have 46 chromosomes in every cell.2 of these chromosomes make us male or female.Female: XX Male: XY
The Sex Chromosomes:Slide3
Has information for male traits.Few other genes.
The Y chromosomeSlide4
Contains many genes, most of which are not on the Y chromosome.This means men only get 1 copy of the gene.
If they get a recessive allele, they show it.
Women need 2 recessive alleles to show disease
Less likely!So, men get “sex-linked” diseases more often.
The X chromosomeSlide5
Colourblindness: Can’t see the difference between certain colours (ex. red and green).Hemophilia: “Bleeders” – don’t produce scabs, so continue to bleed from cuts.
Muscular dystrophy: Muscles lose their ability to repair themselves.
Sex-Linked DisordersSlide6
1. Write a let statement!Let XN
= no disorder X
n
= disorder Y = male2. Determine the parent’s genotypes (letters).
3. Draw Punnett Square.4. Fill in Punnett Square.5. Answer question.
Punnett Squares for Sex-Linked Traits
Write as an Exponent!
No exponent! EVER!Slide7
Colourblindness is a recessive sex-linked trait.Ahmed, who has “normal” vision, marries Sue, who is a carrier (heterozygous) for normal vision.
What is the chance of one of their kids being colourblind?
Solution:
Let XN=not colourblind X
n=colourblind Y=maleAhmed: male not colourblind: XNYSue: female, heterozygous: XN
XnSample ProblemSlide8
X
N
X
n x
XNY
X
N
X
n
X
N
Y
X
N
X
N
X
n
X
n
X
N
X
N
Y
Y
All girls have normal vision, but one is a “carrier”.
Half of the boys will be
colourblind
.
25% of children will be
colourblind
.