5. Blood-type is usually described with a positive/negative phenotype too (for e

Question

5. Blood-type is usually described with a positive/negative phenotype too (for example, AB+, or O-, etc.). The +/- part of the phenotype is due to an independent locus, the Rb locus, with two alleles, which we'll call D and d. Individuals with one or more D alleles are Rh positive, while individuals with two d alleles are Rh negative. The I locus and the Rb locus are totally independent, like seed color and shape for Mendel's peas Consider parents with the genotypes IT Dd and IT DD. a. What is the probability that their first child will have the phenotype AB+? b. What is the probability that their first child will have the phenotype B-? c. What is the probability that their first child will have the phenotype B+?

Explanation / Answer

Parent 1: IBIODd

Phenotype: B+, Since B and D are dominant.

Gamates: IBD, IBd, IOD, IOd

Parent 2: IBIBDD

Gamates: IBD

Phenotype: B+, Since B and D are dominant.

Parent 1    x    Parent 2

IBD

IBd

IOD

IOd

IBD

IBIBDD

IBIBDd

IBIODD

IBIODd

Where,

IBIBDD = B+ phenotype

IBIBDd = B+ phenotype

IBIODD = B+ phenotype

IBIODd = B+ phenotype

Thus, all offsprings will have B+ phenotype, therefore

a. Zero probability that their first child will have the phenotype AB+

b. Zero probability that their first child will have the phenotype B-

c. 100 percent that their first child will have the phenotype B+

IBD

IBd

IOD

IOd

IBD

IBIBDD

IBIBDd

IBIODD

IBIODd

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