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In humans, nearsightedness and phenylketonuria are both inherited as single-locu

ID: 22301 • Letter: I

Question

In humans, nearsightedness and phenylketonuria are both inherited as single-locus autosomal recessive traits that assort independently. Assume that a family has been identified in which both parents were phenotypically normal, but their first child was phenylketonuric and their second child developed nearsightedness.

a. What is the probability that their next child will show both defects? Show your work.

b. What is the probability that their next child will exhibit neither defect? Show your work.

Explanation / Answer

In humans, nearsightedness and phenylketonuria are both inherited as single-locus autosomal recessive traits that assort independently.

Assume that a family has been identified in which both parents were phenotypically normal, but their first child was phenylketonuric and their second child developed nearsightedness.

a. What is the probability that their next child will show both defects? Show your work.

b. What is the probability that their next child will exhibit neither defect? Show your work.

nearsightedness and phenylketonuria are both inherited as single-locus autosomal recessive traits

nearsightedness ---genotype—recessive homozygote ---nn

phenylketonuria ---genotype—recessive homozygote ---pp

parent---------------Nn Pp      x   parent---------------Nn Pp     

NP

Np

nP

np

NP

Np

nP

np

npnp

nearsightedness and phenylketonuria

Answer =1/16

Answer =9/16

NP

Np

nP

np

NP

NP NP

NP Np

NP nP

NP

Np

NP Np

Np Np

Np nP

Np

nP

NP nP

Np nP

nP nP

nP

np

NP np

Np np

nP np

npnp

nearsightedness and phenylketonuria

NP

Np

nP

np

NP

Np

nP

np

npnp

nearsightedness and phenylketonuria