The gene causing Coffin–Lowry syndrome (OMIM 303600) was...

Question

The gene causing Coffin–Lowry syndrome (OMIM 303600) was recently identified and mapped on the human X chromosome. Coffin–Lowry syndrome is a rare disorder affecting brain morphology and development. It also produces skeletal and growth abnormalities, as well as abnormalities of motor control. Coffin–Lowry syndrome affects males who inherit a mutation of the X-linked gene. Most carrier females show no symptoms of the disease but a few carriers do. These carrier females are always less severely affected than males. Offer an explanation for this finding.

Accepted Answer

Hi, everyone. Let's look at our next question. It says if a female with Coffin Lowry syndrome has Children with an unaffected male, what is the probability that a daughter will be affected? So let's think through our bits of information presented here. Coffin Lowry Syndrome is an ex linked recessive treat. And in this case, we have a female with a syndrome since it's a recessive trait on the X chromosome, that means that this female must have two copies of the alley for this, for this syndrome since she is affected and she has two X chromosomes. So we'll just use the letter C for Coffin Lowry and her genotype must therefore be X superscript CX superscript C. And we know that she had Children with an unaffected male. So unaffected mail, who has only one X chromosome, obviously without the mutation causing the syndrome since he only has one X chromosome, even though it's a recessive condition. Uh since he only has the one X, if he had this alley, he would be affected by the condition. So we know that he must be just XY. So we're looking at in terms of their offspring, what is the probability that a daughter will be affected. While daughters of course inherit one X chromosome from each parent. The father well, always pass on an unaffected but the mother because she is homozygous recessive will always pass on an affected X superscript C. So since each parent can only pass on one type of all the daughter's genotypes must always be X XC. They'll be heterozygous carriers for the condition. But there are questions asking us, what is the probability they will be affected? Well, since the father has the unaffected, they will never be affected by the by the disease by the syndrome, since they will always only inherit one copy from their mother. And therefore, there's a 0% chance that they will be affected. So we look at our answer choices. Uh choice A is 0%. So that is our answer. Uh One thing to note is that in the case of sons who would inherit their single X chromosome from their mother. Since the mother can only pass on uh the affected X chromosome, sons have a 100% chance of being affected because they will inherit the mother can only pass on X superscript C and sons only have a single X chromosome. So therefore 100% of the time they will inherit that and express the condition. But daughters probability of being affected choice, a 0%. See you in the next video.

Key Concepts

X-Linked Inheritance

Dosage Compensation

Variable Expressivity

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