Question

An autosomal dominant condition causes deafness in people. However, 40% of people who are known to have at least one copy of the dominant allele have normal hearing (no deafness). Additionally, the severity of deafness varies between individuals with the condition. Some people have complete deafness, some people moderate deafness, and some people only have mild deafness.

The occurrence or not of deafness in people who have at least one dominant allele is an example of:

Codominance

Epistasis

Expressivity

Penetrance

Phenocopy

The severity of deafness in individuals with this condition is an example of:

Codominance

Epistasis

Expressivity

Penetrance

Rett Syndrome is a very rare X-linked dominant disorder thought to be caused by mutations in a gene on the X chromosome. The dominant allele (X^R) causes brain deformation, seizures, and multiple other issues. The recessive allele (X^r) is associated with the non-diseased phenotype:

1) A father that has Rett Syndrome and a mother that is non-diseased have 8 children, 4 sons and 4 daughters.

How many of the daughters would you expect to have Rett Syndrome?

0

1

2

3

4

How many of the sons would you expect to have Rett Syndrome?

0

1

2

3

4

2) A father that is non-diseased and a mother that has Rett Syndrome have 8 children, 4 sons and 4 daughters. It is known that the mother is heterozygous for the Rett alleles

How many of the sons would you expect to have Rett Syndrome?

0

1

2

3

4

How many of the daughters would you expect to have Rett Syndrome?

0

1

2

3

4

3) A couple has 2 sons and 2 daughters. 1 son is non-diseased and 1 son has Rett syndrome. 1 daughter is non-diseased and 1 daughter has Rett syndrome. What are the genotypes of the parents?

Dad is X^RY and mom is X^rX^r

Dad is X^RY and mom is X^RX^r

Dad is X^RY and mom is X^RX^R

Dad is X^rY and mom is X^rX^r

Dad is X^rY and mom is X^RX^r

Dad is X^rY and mom is X^RX^R

Answer 1

1). d. Penetrance

Penetration is the degree of expression of an inherited trait in an individual. Of all the people who inherit the trait express the trait means, the penetrance is 100%. If only 70% of the people who inherit the trait express the gene means, the penetrance is 70%, this is known as reduced penetrance or incomplete penetrance. In the given case, some of the people with the dominant allele are not become deaf due to the incomplete penetrance of the gene.