Question

A woman (Tina) has a certain genetic condition (is affected). She goes to a genetic counselor to learn about the inheritance pattern of the condition and to ascertain the chance that she might pass it to her offspring. The following is the information she gives the Genetic Counselor. (assume that this condition displays 100% penetrance, results from a single genetic mutation and exhibits complete dominance)

1) Tina is the fourth born of seven children. Her oldest sibling is an affected sister followed by a brother then a sister, neither of whom is affected. Tina’s younger siblings include an unaffected brother and fraternal twins- one girl and one boy- the youngest of Tina’s siblings. The male twin is affected while the female is not.

2) Tina’s oldest sister has five children with an unaffected man who has no family history of the condition. The oldest is a male followed by identical twins (both girls) another daughter and a son (the youngest). None of these individuals is affected.

3) Tina’s affected brother has two children, a girl (the oldest) and a boy, with a woman who has no family history of the trait. Neither of these children is affected.

4) Neither of Tina’s parents are affected.

5) Tina’s mother is the youngest of five children in her family. Tina has two maternal aunts (first and fourth born) and two maternal uncles. None of Tina’s maternal aunts or uncles is affected.

6) Tina’s maternal grandmother is deceased while all of her other grandparents are living. Her maternal grandfather has the condition while her maternal grandmother did not.

7) Tina’s father is the oldest of five children, none of whom have the condition (is affected).

8) Tina’s paternal grandmother has the condition while her paternal grandfather does not.

Draw a pedigree using the information above to answer the following questions. You will not be submitting the pedigree itself.

1. (2 points) What is the most likely inheritance pattern for the trait. (i.e. whether the condition is dominant or recessive and if the gene responsible for it is located on an X chromosome or an autosome). Only one pattern is possible (consistent with all of the data given) you may want to use the process of elimination for part of this determination

2. (1 point) One inheritance pattern that is not the one represented in this pedigree is X-linked recessive. What is something about the pattern that shows that it cannot represent X-linked recessive inheritance?

Answer 1