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Determine the genotype of the albino child.

Biology

ScanSolve AI Answer

Answer

b

56\frac{5}{6}

Step-by-step solution

7 steps

Part a· 3 steps

Let 'A' represent the dominant allele for normal skin colour and 'a' represent the recessive allele for albinism.

  1. Determine the genotype of the albino child.

    Since albinism is a recessive trait, an albino individual must have two copies of the recessive allele.
    Albino child genotype: aaaa

  2. Determine the probable genotypes of the parents.

    Both parents have normal skin colour (dominant phenotype) but produced an albino child (aa). This means each parent must have contributed an 'a' allele to the albino child. Therefore, both parents must be heterozygous carriers.
    Man's genotype: AaAa
    Woman's genotype: AaAa

  3. Determine the probable genotypes of the other children.

    When two heterozygous parents (Aa x Aa) cross, the possible genotypes of their offspring are:

    1/4AA:1/2Aa:1/4aa1/4 AA : 1/2 Aa : 1/4 aa

    The two children with normal skin colour could have genotypes AA or Aa.

    Probable genotypes:

    • Parents: Man (Aa), Woman (Aa)
    • Children: One albino (aa), two normal skin (AA or Aa)

    Pedigree Diagram (text description):
    Generation I:
    Male (normal skin, carrier) -- Female (normal skin, carrier)
    Genotypes: Aa -- Aa

    Generation II:
    Offspring:

    1. Child (normal skin): Genotype AA or Aa
    2. Child (normal skin): Genotype AA or Aa
    3. Child (albino): Genotype aa

Part b

56\frac{5}{6}

  1. Determine the possible genotypes of a boy with normal skin colour from the parents (Aa x Aa).

    The cross Aa x Aa produces offspring with genotypes: 1 AA : 2 Aa : 1 aa.
    Among the offspring with normal skin colour (AA and Aa), the ratio is 1 AA : 2 Aa.
    So, the probability that a normal-skinned boy is AA is 13\frac{1}{3}.
    The probability that a normal-skinned boy is Aa is 23\frac{2}{3}.

  2. Identify the genotype of the girl.

    The girl is a carrier for the albino gene, so her genotype is AaAa.

  3. Calculate the probability that their first child will have normal skin colour.

    We consider two scenarios for the boy's genotype:

    Scenario 1: The boy is AA (probability 13\frac{1}{3}).
    Cross: AA×AaAA \times Aa
    Offspring genotypes: 1/2AA,1/2Aa1/2 AA, 1/2 Aa
    All offspring (100%) will have normal skin colour.
    Probability of normal skin in this scenario = 1.
    Contribution to total probability = 13×1=13\frac{1}{3} \times 1 = \frac{1}{3}.

    Scenario 2: The boy is Aa (probability 23\frac{2}{3}).
    Cross: Aa×AaAa \times Aa
    Offspring genotypes: 1/4AA,1/2Aa,1/4aa1/4 AA, 1/2 Aa, 1/4 aa
    Offspring with normal skin colour (AA or Aa) = 14+12=34\frac{1}{4} + \frac{1}{2} = \frac{3}{4}.
    Probability of normal skin in this scenario = 34\frac{3}{4}.
    Contribution to total probability = 23×34=612=12\frac{2}{3} \times \frac{3}{4} = \frac{6}{12} = \frac{1}{2}.

  4. Add the probabilities from both scenarios.

    Total probability of the first child having normal skin colour = 13+12=26+36=56\frac{1}{3} + \frac{1}{2} = \frac{2}{6} + \frac{3}{6} = \frac{5}{6}.

    The probability that their first child will have normal skin colour is 56\boxed{\frac{5}{6}}.

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