Question #a5cdf
1 Answer
Oct 2, 2015
The easiest way to solve a pedigree question is to first look for the trait being dominant/recessive and then check for autosomal or X-linked inheritance
Explanation:
**
- Step 1:
Determine whether the disorder is dominant or recessive: **- If the disorder is dominant, one of the parents must have the disorder. - If the disorder is recessive, neither parent has to have the disorder because they can be heterozygous.
**
- Step 2:
** - *Determine if the pedigree chart shows an autosomal or Xlinked
disease:* *- If most of the males in the pedigree are affected, then the disorder is X-linked. - If it is a 50/50 ratio between men and women the disorder is autosomal.
* * Rules of Inheritance: * *
Autosomal Recessive:
- Appears in both sexes with equal frequency.
- Trait tend to skip generations.
- Affected offspring are usually born to unaffected parents.
- When both parents are heterozygous, approx. 1/4 of the progeny will be affected.
- Appears more frequently among the children of consanguinous marriages.
Autosomal Dominant:
- Appears in both sexes with equal frequency.
- Both sexes transmit the trait to their offspring.
- Does not skip generations.
- Affected offspring must have an affected parent unless they posses a new mutation.
X-Linked Dominant:
- Both males and females are affected; often more females than males are affected.
- Does not skip generations.
- Affected sons must have an affected mother; affected daughters must have either an affected mother or an affected father.
- Affected fathers will pass the trait on to all their daughters.
- Affected mothers if heterozygous will pass the trait on to 1/2 of their sons and 1/2 of their daughters.
X-Linked Recessive:
- More males than females are affected.
- Affected sons are usually born to unaffected mothers, thus the trait skips generations.
- Approximately 1/2 of carrier mothers’ sons are affected.
- It is never passed from father to son.
- All daughters of affected fathers are carriers.
Besides this one should check for Y-linked dominant and mitochondrial disease as well.