Pedigrees
Pedigree rules and tips
How do you recognize autosomal recessive traits in pedigrees.
Common for affected individuals to be born to unaffected parents.
Affected individuals will include both males and females equally.
If the condition is rare most people do not carry an abnormal allele and those that do, carry it in the heterozygous form.
If both parents are affected, then all children are affected.
Not seen in every generation.
How do you recognize autosomal dominant traits in pedigrees.
Affected individuals will have an affected parent.
Males and females will be affected equally.
Either sex transmits the allele.
If one parent is affected and other is not the expected frequency is approximately 50/50 in offspring of affected and unaffected.
Two unaffected parents will never have affected children.
Two affected parents can have an unaffected offspring. Often dominant traits occur in the heterozygous condition as two dominant (mutant) alleles can be fatal. This is not the case for all diseases though.
How do you recognize X-linked recessive traits in pedigrees.
More males are affected than females.
If a female is affected, then all males will be affected, and all females will be carriers assuming the biological father is normal.
If a male is affected all daughters will be carriers and no sons will be affected
If a male is unaffected, no female offspring will be affected
No male carriers
How do you recognize X-linked dominant traits in pedigrees.
An affected female passes the trait to 50% of offspring
An affected male passes the condition to 100% of daughters but never to sons
How do you recognize Y-linked traits in pedigrees.
100% of affected individuals are male.
If the father is affected, all sons are affected (This differentiates from x-linked recessive)
How to recognize mitochondrial inheritance patterns in pedigrees.
If a mother is affected, all offspring are effected.
If a father is effected NONE of his offspring are effected.