Question

Why is the answer c? I thought since Sam and Emily are children of Dan and Sara, there would be a 1/2 chance that they could get the rare deletion. Therefore, I thought that if Sam and Emily have children with someone else, there would be a 1/4 chance their children could have the disease. Please provide an explanation.

Dan has a disease that is caused by a rare deletion of a paternally imprinted gene. Dan has children with Sara, who does not have the disease. Dan and Sara’s son Sam and daughter Emily don’t have the disease. Sam then has a child with a woman named Jolie and Emily has a child with a man named Jordan. What’s the probability for Sam’s or Emily’s children have the disease?

a. Sam’s child: 0; Emily’s child: 0
b. Sam’s child: 0.25; Emily’s child: 0.25 c. Sam’s child: 0; Emily’s child: 0.25
d. Sam’s child: 0.25; Emily’s child 0
e. Sam’s child: 0.5; Emily’s child: 0.5

Answer 1

Solution:

option C is correct.

As this question is related genomic imprinting.

• Paternal imprinting means the allele of a particular gene inherited from father is silent and the maternally inherited allele is active.

For a paternally-imprinted gene:

Egg: ----(+)---- X Sperm :   ----(+)---- imprinted

girl progeny:  ----(+)----m Son progeny:  ----(+)---- m

  ----(+)----p imprinted ----(+)----p imprinted

After oogenesis and spermatogenesis :

Gametes: (Egg) ----(+)----    Sperm :   ----(+)---- imprinted

Explanation:

• Dan and Sara’s son Sam and daughter Emily are normal as alleles inherited from father are silent. They inherit an active allele from their mother.
• Emily can produces gamete with rare deletion allele get from her father is 25% which can be expressed in her child as it will be active now.
• While Sam can also produces gamete with rare deletion allele from father is 25%, but it will remain silent due to imprintin . Hence it will not expressed in his child.