Download Ch. 10.5 Sex-Linked Traits

Sex-linked Traits
Ch. 10.5
Sex chromosomes
• Humans- 23rd pair of chromosomes- X,Y
• Eggs- Have an X chromosome.
• Sperm- Half have an X chromosome, half have
a Y chromosome.
– Fathers determine gender(sex) of offspring.
• Males- XY
• Females- XX
• 50% chance of having a girl or boy offpring.
Sex-linked genes
• Any gene on a sex chromosome- X or Y.
• Majority are on X chromosome.
• Examples– Eye color in fruit flies- on the X chromosome
• Red color is Normal and Dominant, XR
• White color is Recessive. Xr
• Females must have 2 recessive alleles to have white
eyes. Xr Xr
• Males need just 1 recessive allele ( they have only 1 X
chromosome) Xr Y to have white eyes.
Eye Color in
Fruit flies
Human X-linked recessive traits.
• Hemophilia- bleeding disorder
• Red-green color blindness.
– more males with the disorder compared to females.
– Females can be carriers- have one recessive allele- do not have
the disorder, but can pass on the recessive allele to offspring.
– Mothers pass trait on to sons.
• Pedigree- Chart used to record and trace the occurrence of
a trait in a family.
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Squares- males
Circles- females.
Colored shapes- individuals that show the trait.
Parents are connected by horizontal lines(marriage line)
Children beneath them.
Generations – designated by Roman Numerals ( I, II, III etc)
Individuals are Numbered left to right in each generation.
Sex-linked recessive pedigree
skips generations , see more often in males.