Biology 10 - Study Guide for Exam 3

 

Autosomal Recessive
•Males and females equally affected
•1/4 of offspring will be affected
•Trait typically found in siblings, not parents
•Parents of affected children may be related
•Trait may appear as isolated event in small families.

Autosomal Dominant

•Every affected individual should have at least 1 affected parent
•Affects males and females equally
•Affected individuals may have unaffected children (Aa x Aa produces 25% aa)
•Homozygous dominant condition is often fatal
•Difficult to determine with small families

X-linked Dominant

•The trait is never passed from father to son.
•All daughters of an affected male and a normal female are affected. All sons of an affected male and a normal female are normal.
•Matings of affected females and normal males produce 1/2 the sons affected and 1/2 the daughters affected.
•Males are usually more severely affected than females. The trait may be lethal in males.
•In the general population, females are more likely to be affected than males, even if the disease is not lethal in males.

X-linked Recessive

•As with any X-linked trait, the disease is never passed from father to son.
•Males are much more likely to be affected than females. If affected males cannot reproduce, only males will be affected.
•All affected males in a family are related through their mothers.
•Trait or disease is typically passed from an affected grandfather, through his carrier daughters, to half of his grandsons.

Y-linked

•Affects only males, carriers usually express the trait
•Passed directly from father to son

Mitochondrial

•Passed directly from an affected mother to all offspring
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•Only females pass trait on