Autosomal recessive
- Need 2 copies of the allele to have the trait/disorder
- Males and females are affected equally, usually in equal proportions (if there are enough people in the pedigree)
- Trait tends to skip generations
- When both parents are heterozygous, ~¼ of offspring will be affected
- When both parents are homozygous, all children will be affected
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Autosomal dominant
- Need only 1 dominant allele to have the trait/disorder
- Males and females are affected equally
- Does not skip generations
- Affected offspring must have an affected parent (unless they have a new mutation)
- When 1 parent is affected (heterozygous) and the other is unaffected, ~ ½ of the offspring will be affected
- Unaffected parents do not transmit the trait
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X-linked recessive
(gene is on the X chromosome)
- Need 2 copies of the allele to have the trait/disorder
- ~½ of the carrier (heterozygous) mother’s sons are affected
- Trait can skip generations
- More males than females are affected
- 100% of daughters of affected fathers are carriers
- Never passed from father to son
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X-linked dominant
(gene is on the X chromosome)
- Need only 1 dominant allele to have the trait/disorder
- All daughters of an affected male will be affected
- Affected mothers (if heterozygous) will pass the trait on to ½ of both sons and daughters with each pregnancy
- Both males and females are affected; often more females than males are affected
- Less common inheritance pattern than the X-linked recessive
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