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    BMAT 2009 S2

    BMAT 2009 S2

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    This section is Section 2 of 3.

    Speed as well as accuracy is important in this section. Work quickly, or you might not finish the paper. There are no penalties for incorrect responses, only marks for correct answers, so you should attempt all 27 questions. Each question is worth one mark.

    You must complete the answers within the time limit. Calculators are NOT permitted.

    Good Luck!

    Individual A in the family pedigree below is homozygous dominant and individual B is homozygous recessive for a particular feature.

    1. What is the percentage probability that individual F is homozygous recessive if:
    • 1
    0

    Explanation

    The correct answer is C.

    Let dominant allele = P, recessive allele = p.

    A: homozygous dominant = PP; B: homozygous recessive = pp

    P P
    P Pp

    Pp

    p

    		 Pp

    Pp

    C and D are 100% heterozygous dominant. For F homozygous recessive:

    1. i) E is homozygous recessive:

    E alleles = pp

    P p
    p Pp

    pp

    p

    		 Pp

    pp

    Ratio = 1 (PP) : 1 (pp)

    Hence, there is a 50% probability that F is homozygous recessive

    1. ii) E heterozygous:

    E alleles = Pp

    P p
    P PP

    Pp

    p

    		 Pp

    pp

    Ratio = 1 (PP) : 2 (Pp) : 1 (pp) – 1+2+1=4. pp = 1⁄4

    Hence, there is a 25% probability that F is homozygous recessive

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