Genetic q

[MudPhud20XX]

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Anyone, who is good at this can you help me with this q?

A 27-year old G1P0 at 12 weeks gestation presents to her obstetrician for her first prenatal visit. She and her husband both have achondroplasia, and she is curious what are the chances that they will have a child of average height. What percent of children of two individuals with achondroplasia will be expected to be of average height?
1)25
2)50
3)33
4)75

 

[EazyE1907]

answer should be 33%. You have to know that achondroplasia is a autosomal dominant disorder. So if the two parents have the disease they would have to be heterozygous for the dominant allele, meaning Dad = Aa and mom = Aa. If you set up the punnet square, you would have one child Homozygous for the dominant allele, which would be incompatible with life. so you would be left with two children having the disease being Aa and the other child aa which would be of average height. so 1 out 3 would have average height. 33% should be the answer unless i am missing something.

 

[MudPhud20XX]

answer should be 33%. You have to know that achondroplasia is a autosomal dominant disorder. So if the two parents have the disease they would have to be heterozygous for the dominant allele, meaning Dad = Aa and mom = Aa. If you set up the punnet square, you would have one child Homozygous for the dominant allele, which would be incompatible with life. so you would be left with two children having the disease being Aa and the other child aa which would be of average height. so 1 out 3 would have average height. 33% should be the answer unless i am missing something.

Ah... that makes sense, so it's that 2/3 thing that my genetic prof was talking about! Thanks! Yes the answer is 33%!

 

[Distant]

Is there like a list of Autosomal Dominant Diseases where the patient with homozygous Diseased allele wont Survive? Or is it a general rule where most AD Disease are that way by deafult

 

[MudPhud20XX]

Is there like a list of Autosomal Dominant Diseases where the patient with homozygous Diseased allele wont Survive? Or is it a general rule where most AD Disease are that way by deafult

Good q. I am not sure since I haven't covered all the path yet. Has anyone seen any genetic question that was similar to achondroplasia?

 

[EazyE1907]

It is by default. Usually ppl who are Homozygous dominant for the disease dont live past a couple months.

Exception is being homozygous dominant for familial hypercholestrolemia. Homozygous individuals for this dis will live past infancy but will have symptoms that arise earlier in adulthood. Progression to atherosclerosis will be much faster when compared to heterozygous individuals. They will also have a risk of developing MI before age 20 and have tendon xanthomas and corneal arcus lipid accumulations (you won't see xanthoma's and such in heterozygous individuals, and that's very HY to know) . I remember there was a tricky kaplan genetic Q giving you familial hypercholestrolemia with a patient with xanthoma's and you had to remember that this person was homozygous dominant not heterozygous dominant or elese you would get the question wrong. Hope this helped.

 

[seminoma]

It is by default. Usually ppl who are Homozygous dominant for the disease dont live past a couple months.

Exception is being homozygous dominant for familial hypercholestrolemia. Homozygous individuals for this dis will live past infancy but will have symptoms that arise earlier in adulthood. Progression to atherosclerosis will be much faster when compared to heterozygous individuals. They will also have a risk of developing MI before age 20 and have tendon xanthomas and corneal arcus lipid accumulations (you won't see xanthoma's and such in heterozygous individuals, and that's very HY to know) . I remember there was a tricky kaplan genetic Q giving you familial hypercholestrolemia with a patient with xanthoma's and you had to remember that this person was homozygous dominant not heterozygous dominant or elese you would get the question wrong. Hope this helped.

Agree with this except for the part about tendon xanthomas in FH heterozygotes. You absolutely do see tendon xanthomas in heterozygotes.

 

[EazyE1907]

Agree with this except for the part about tendon xanthomas in FH heterozygotes. You absolutely do see tendon xanthomas in heterozygotes.

Yeah your right. I actually thought/knew the same. However, the kaplan explanation was saying that you won't see them in heterozygotes, maybe they meant fewer xanthomas But hetero's having them def makes more sense.

 

[seminoma]

Yeah your right. I actually thought/knew the same. However, the kaplan explanation was saying that you won't see them in heterozygotes, maybe they meant fewer xanthomas But hetero's having them def makes more sense.

Yeah Kaplan does that to me sometimes too.. They had me convinced of something really dumb recently.