Pedigree Charts and Sex-linked Traits
Pg 61
• Polygenic traits –
Traits that are controlled by
more than 1 gene
Ex: height, weight, skin color,
intelligence, behavior, etc.
Carrier – a person who
carries a recessive gene for a
disease, but does not show
it. (heterozygous)
Pg 60
Listen to the song, and try to draw the pedigree
chart that goes with it 
Pg 60
• Copy this pedigree chart, and use it to figure
out the family’s genotypes.
Notes pg 61
• Sex-linked traits – carried on the X
chromosome.
• It is easier for a male to have an X-linked
trait than for a female
Sex-linked Key
• X X – normal Female
• X Y – normal Male
• X Xa – Carrier Female
• Xa Xa – Female with the trait (disease)
• Xa Y – Male with the trait (disease)
(males can NOT be carriers)
• In flies, red eyes( R) is dominant over
white eyes (r).
• X RXr
• X RXR
• XRY
• XrY
What would you get if you crossed a
heterozygous red-eyed female with a redeyed male?
• If a female who is a carrier for color-blindness
marries a normal male, what is the probability
their children will be color-blind?