Examples Sickle cell disease is caused by a recessive allele (s) causing abnorma

Question

Examples Sickle cell disease is caused by a recessive allele (s) causing abnormal hemoglobin to be made.This cells to become "sickle" shaped, making them clog blood vessels and preventing them from with sickle cell disease have severe anemia and weakness. S represents the Heterozygotes are carriers for sickle cell trait and do exhibit some symptoms. dominant allele for normal hemoglobin. Analyze genotypes and phenotypes of children from the following matings using Punnett squares. 1. Cross: SS xss Phenotypic ratio Genotypic ratio 2. Cross: Ss x Ss Genotypic ratio Phenotyoic ratio 3. Cross: ss x ss Genotypic ratio Phenotypic ratio Cross: SS x ss S x Genotypic ratio Phenotypic ratio If you were genetic counselor what would you tell prospective parents who were both carriers for sickle cell trai (i.e. "There is a carrier for sickle cell disease.) % chance your child will have sickle cell disease and a 96 chance they same analysis for Huntington's disease (see above). If you were a genetic counselor what would you te o the spective parents, one of whom had Huntington's disease?

Explanation / Answer

S

S

s

Ss

Ss

s

Ss

Ss

1. Genotype: All Ss. Phenotype: All carriers

S

s

S

SS

Ss

s

Ss

ss

2. Genotype: SS : Ss : ss :: 1:2:1. Phenotype: Normal : carrier : diseased :: 1:2:1.

s

s

s

ss

ss

s

ss

ss

3. Genotype: All ss. Phenotype: All diseased

S

s

s

Ss

ss

s

Ss

ss

4. Genotype: Ss : ss :: 1:1. Phenotype: Carrier : diseased :: 1:1

If both parents are carriers, the ratio will be SS : Ss : ss :: 1:2:1, as shown in answer 2 above. Thus, there will be 25% chances that they are diseased and 50% chances that they are carriers.

Huntington’s disease is an autosomal dominant disorder. If one of the parents is diseased, the chances of the progeny having the disease are 50%.

H

h

h

Hh (disease)

hh (normal)

h

Hh (disease)

hh (normal)

S

S

s

Ss

Ss

s

Ss

Ss

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