Quick genetics question

[AznSeal]

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It's for a test I have tomorrow.

The question I have is from the study guide on this: In children that express recessive genetic diseases, such as cystic fibrosis, it has been occasionally found that only one parent is heterozygous for the disease allele. In these cases, it has also been confirmed that the parents are the true biological parents of the affected child. Offer a genetic explanation for this observation.

My initial explanation was that the other parent could simply be homozygous for the disease and the child inherited a copy of the recessive allele from each parent but I feel like it's too simple.

Does it have something to do with X-linkage and the child having Turner Syndrome (or something else of that nature) or 2 nondisjunctions happened during meiosis so the child ended up with 2 copies of the recessive allele from one parent and 0 copies of the allele from the other?

Thanks

 

[chillaxbro]

Spontaneous mutation of the good allele?
Deletion/inversion of one of the arms of the good chromosome?

 

[113]

It's for a test I have tomorrow.

The question I have is from the study guide on this: In children that express recessive genetic diseases, such as cystic fibrosis, it has been occasionally found that only one parent is heterozygous for the disease allele. In these cases, it has also been confirmed that the parents are the true biological parents of the affected child. Offer a genetic explanation for this observation.

My initial explanation was that the other parent could simply be homozygous for the disease and the child inherited a copy of the recessive allele from each parent but I feel like it's too simple.

Does it have something to do with X-linkage and the child having Turner Syndrome (or something else of that nature) or 2 nondisjunctions happened during meiosis so the child ended up with 2 copies of the recessive allele from one parent and 0 copies of the allele from the other?

Thanks

The most likely (in fact, for cystic fibrosis, confirmed) explanation for these observations is an uncommon condition called uniparental disomy in which both of one of the chromosomes are inherited from the same parent. Uniparental disomy is thought to originate from trisomic embryos that lose one of their chromosomes early during development and retain the two remaining chromosomes from the same parent.

Good luck with your test.

 

[AznSeal]

The most likely (in fact, for cystic fibrosis, confirmed) explanation for these observations is an uncommon condition called uniparental disomy in which both of one of the chromosomes are inherited from the same parent. Uniparental disomy is thought to originate from trisomic embryos that lose one of their chromosomes early during development and retain the two remaining chromosomes from the same parent.

Good luck with your test.

Thank you so much!

Someone else explained it to me like that as well so I appreciate the help. My other question is can UPD be caused by nondisjunction?

 

[113]

Thank you so much!

Someone else explained it to me like that as well so I appreciate the help. My other question is can UPD be caused by nondisjunction?

Yes.

 

[yehhhboiii]

Another possibility is gene silencing (epigenetics) where the gene from only one chromosome is expressed because post translational modifications (ubiquitination of histones) turns off gene expression in the other.

 

[mmmcdowe]

SDN is not the place for HW help, closing thread.