IB Biology SL D3.2 Inheritance questions

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Question 1

Paper 2Hard16 marks

A family has several members diagnosed with phenylketonuria (PKU). Figure 1 shows their pedigree. No other family members are shown.

IIIIIII-1I-2II-1II-2II-3III-1III-2malefemalediagnosed with PKUnot diagnosed with PKU

Use P for the allele not associated with PKU and p for the PKU-associated allele.

(a)

Using Figure 1, state two observations that support PKU having an autosomal recessive inheritance pattern in this family.

[2]
(b)

Deduce the genotypes of I-1, I-2, II-2 and II-3.

[3]
(c)

Show the genetic cross for a child of II-2 and II-3, and state the probability that this child has PKU.

[3]
(d)

III-2 does not have PKU. Determine the probability that III-2 is a carrier of the p allele. Show your reasoning.

[3]
(e)

Suppose III-2 has a child with a person known to be a Pp carrier. Determine the probability that their child will have PKU. Use your answer to part (d).

[2]
(f)

Explain how inheritance of the p allele can result in PKU and affect the conversion of phenylalanine to tyrosine.

[3]

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