Question

Fill-ins. Type the one BEST word or short phrase into the answer box.

Duchenne muscular dystrophy is caused by an X-linked recessive mutation in the DMD gene, which encodes the protein dystrophin. A female without the disease mates with a male with Duchenne muscular dystrophy; they have two sons and two daughters. The first son has the disease as does their first daughter. Based on this, the probability that the second son will have the disease is ____________. The probability that the second daughter will be a carrier is __________________.

Answer 1

Duchenne muscular dystrophy (DMD) is a progressive type of muscular dystrophy that occurs predominantly in males although it may affect females in rare cases. DMD causes skeletal and heart muscles to become weak and weaken (atrophic). DMD is caused by changes (mutations) in the gene DMD. The protein dystrophin DMD gene codes. Dystrophin is primarily developed in skeletal and heart muscle cells.

Muscular dystrophy is an X-Linked recessive disease that occurs primarily in males and rare in females.

	Xd	Y
X	XXd	XY
Xd	XdXd	XdY

XdY- Father

XdX- Mother

XY- Normal som

XdY- Son which has muscular dystrophy

XdXd- Affected daughter

XXd- Carrier daughter

In the question, a condition is mentioned that their one son and one daughter are affected which means the mother is a carrier because if the mother is normal without the carrier gene then it is not possible that no daughter will be affected. so the genotype of Father and Mother is XdY and XdX respectively.

So from the cross, we can see that half half of the progeny is normal and half of them is unaffected.

So there is 1/4 chance of every possible condition for the sons and daughters .

In the case of daughter one is affected and one is carrier same in case of sons in which one is normal and one is affected.

So, the probability of next sone to be affected is 1/4 and the next daughter to be a carrier is also 1/4 . Probability does not gets affected by the previous results