3. The pedigree chart right shows the inheritance of the allele B in a mammal th

Question

3. The pedigree chart right shows the inheritance of the allele B in a mammal that can have a coat color of black or white. Answer the questions below (a) Which color is produced by the dominant allele (black or white)? (b) Explain how you know this: 4. Autosomal recessive tralts Albinos lack pigment in the hair, skin and eyes. This trait is inherited as an autosomal recessive allele (i.e. it is not carried on the sex chromosome). Albinism in humans (a) Write the genotype for each of the individuals on the chart using the following letter codes: PP normal skin color; P- normal, but unknown if homozygous; Pp carrier; pp albino. (b) Why must the parents (I-3) and (1-4) be carriers of a recessive allele:

Explanation / Answer

3a. The dominant allele is responsible for white color.

b. This is because II-4 and II-5 are unaffected but one of their progeny is affected. So, they must be carriers.

4. I1 = PP

I2 = pp

I3 = pp

I4 = PP

II1 = Pp

II2 = Pp

II3 = Pp

II4 = Pp

II5 = Pp

III1 = PP/Pp

III2 = pp

III3 = PP/Pp

III4 = PP/Pp

b. A recessive allele can not exert its effect if it is in a heterozygous condition. If any of the progeny of II-3 and II-4 have to show mutant phenotype, both the parents must contain at least one recessive allele.

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