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Home Q & A Board Biology-Related Homework Help Genetics and Developmental Biology
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rld09009 rld09009
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11 years ago
Why do they specifically have to be both heterozygous, and not one heterozygous one homozygous recessive?
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wrote...
#1
11 years ago
say what?
wrote...
#2
11 years ago
If they had the disease, they wouldn't have reproduced.

If they didn't have one one copy of the gene, then the kid couldn't possibly get the two required (one from each parent).

Consequently, each parent must have one copy of the gene.
wrote...
#3
11 years ago
i don't know why. sorry i couldn't help you. but at least i get points.
wrote...
#4
11 years ago
One has to be heterozygous and the other can be either heterozygous or homozygous for the autosomal trait which is recessive

Heterozygous means that they have a trait for a normal allele and the autosomal allele but the normal allele is dominant so the autosomal disease allele is recessive so it doesn't show up.

If they were homozygous dominant with a normal allele there is no chance that any child has the condition since they cannot pass on an allele they do not have.
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#5
11 years ago
I think the underlying assumption in your question is that both parents are "healthy."  Assuming pure Mendelian principles, the parent who exhibits homozygous recessive alleles will have this disease.  So, frankly, it depends if your questions assumes that both parents are healthy.
wrote...
#6
11 years ago
You can have a child with an autosomal recessive disease if one parent is homozygous recessive  and the other is heterozygous.  I can't do a punnett square on this thing, but odds are 50%.  If the parents had two children you'd expect one to be heterozygous and the other to be homozygous recessive In a heterozygous x heterozygous match the odds of getting a homozygous recessive child would be 25%.  50% of the children would be expected to heterozygous and 25% would be homozygous dominant.
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