2: Risk Assessment

what is the main purpose of a Punnet square in genetics?

to determine carrier risk and recurrence risk

what is an individual who is known to carry a specific mutant allele called?

obligate carrier

in the context of autosomal recessive disorders, who are considered obligate carriers?

the parents of the affected individual

what kind of risk is the chance that a future pregnancy will result in an affected child?

recurrence risk

for a couple with an affected child, what is the recurrence risk for future pregnancies in an autosomal recessive disorder?

1/4

what is the chance that an unaffected child of carrier parents will be a carrier for an autosomal recessive disorder?

2/3

how is risk assessed in an autosomal recessive disorder?

(each parent’s risk of being a carrier) x (each parent’s risk of passing on the mutant allele)

what is the key assumption regarding unaffected spouses from outside the family in autosomal recessive disorders

they are not carriers unless otherwise indicated

who are considered obligate carriers in X-linked recessive disorders?

the mothers of affected males and daughters of affected males

what is a key assumption about male genotypes in X-linked recessive disorders?

male genotypes can be determined by their phenotypes

how is risk assessed for an X-linked recessive disorder when the father is unaffected?

(mother’s risk of being a carrier) x (risk of passing on the mutant allele) x (risk the baby will be male)

what is the key assumption for affected individuals in autosomal dominant disorders?

affected individuals are heterogenous

how is mitochondrial DNA inherited?

mother

what are the two main rules for inheritance in mitochondrial DNA disorders?

• all children of affected females will be affected

• no children of affected males will be affected