Pedigree analysis

Autosomal recessive traits

• Appear with equal frequency in males and females.
• Appear when a person inherits two alleles for a trait, one from each parent.
• When both parents are heterozygotes, ¼ of the offspring express the trait.
• Appear more in consanguinious couples.
• Affected children are commonly born to unaffected parents (carrier)
• Tend to skip generation
• E.g., tay-sach

Autosomal dominant trait

• Doesn't skip generation
• Appear equally in both sexes
• Affected child has an affected parent
• If one parent is heterozygous for the trait and other is unaffected, ½ of the offspring will be affected.
• E.g., familial hypercholesterolemia

X-linked recessive trait

• Appear more frequently in males than female
• Affected males are born to unaffected mother
• Tend to skip generation
• Heterozygous mother gives ½ sons affected and ½ daughter as unaffected carriers.
• Not passed from father to son
• E.g. hemophilia A

X-linked dominant trait

• Appear equal in male and female but affect more female than male
• Must affected parents
• Do not skip generation
• Affected father pass trait to all daughters and none of the son.
• Affected mother pass to ½ sons and ½ daughters.
• E.g hypophosphatemia I or familial vitamin D resistant rickets.

Y-linked traits

• Only males are affected
• Trait is passed from father to son .
• Does not skip generation
• E.g. maleness