destroyer bio 221

[d wannabe]

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Sickle cell anemia is an autosomal recessive trait.
If two individuals are heterozygotes, what is the risk of having an affected child from a single mating?

The answer is 25%

But shouldn't it be 50%?
50% normal child and 50% affected?

 

[Danny289]

Sickle cell anemia is an autosomal recessive trait.
If two individuals are heterozygotes, what is the risk of having an affected child from a single mating?

The answer is 25%

But shouldn't it be 50%?
50% normal child and 50% affected?

think about phenotype

 

[cougarblue84]

One one in four, statistically, will get both recessive genes with two people that are heterozygous for the trait. If you draw up a Punnet square with Aa X Aa you'll see that only one child has both recessive.

 

[Dotoday]

Person must be homozygous for the trait in order to get the disease since the trait is recessive. Therefore, if both parents are heterozygous, then each one has 0.5% chance of transmitting the diseased allele. You do 0.5* 0.5 = 0.25. 0.25*100 = 25%.

 

[Simiam]

---S---- s
S -SS-- Ss
s -Ss--- ss


1 Homozygotic Dominant
2 Heterozygotes
1 Homozygotic Recessive