A severe form of tooth loss tooth agenesis defined as missin

A severe form of tooth loss (tooth agenesis), defined as missing six or more teeth, is a rare inherited condition. A research group has been studying tooth agenesis in a Finnish family (see diagram below).

A) List the outsiders in the family tree below.

B) Based on the allele frequency for this trait in the population, what assumptions would you make about the genotype of each outsider in this family tree if you were expecting it to be a recessive trait? Explain your reasoning.

C) You collect phenotypic data from the living family member and determine that the following family members have tooth agenesis

Affected member of this family are: II2, II4, II7, II8, III2, III4, III5, III7, III8, IV1, IV2

Which, if any, modes of inheritance may be ruled out for this family? Briefly explain your reasoning for each mode you rule out (see table on next page).

(part C continued)

Rule out?

Yes or No

Rationale

autosomal dominant

autosomal recessive

X-linked dominant

X-linked recessive

D) Are the two sets of twins in this family identical or fraternal twins? What is the basis of your answer?

E) If III-2 and III-7 married and had a child, what is the probability that their child would have tooth agenesis? State the mode of inheritance that you think is most likely for this tree. Show your calculations based on that mode of inheritance.

Mode of Inheritance:

Probability:

Solution

Ans A:

Self-evident from the given family-tree, 3,5,6,9 in generation II and 1 in generation III are the outsiders in the family tree.