Albinism (lack of pigment) is caused by a recessive allele in humans. If normal parents have an albino child, what is the probability that their next child will be normal for pigment?
N = normal gene, a = albino
Both parents must be Na. Use a Punnett square.
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To determine the probability of the next child being normal for pigment, we need to understand the genetic makeup of the parents. Since albinism is caused by a recessive allele, let's assume that the normal parents have the genotype Nn (N for the normal allele and n for the albino allele).
In this case, if the parents have an albino child, it means that both parents passed on their recessive albino allele (nn) to the child. Therefore, the genotype of the child must be nn.
To calculate the probability of the next child being normal for pigment (having the genotype Nn), we need to consider the possible genetic combinations the parents can produce:
The father's genotype: Nn (normal allele, albino allele)
The mother's genotype: Nn (normal allele, albino allele)
When these two parents mate, there are four possible combinations of the alleles they can pass on to their child:
1. Father: N (normal allele) + Mother: N (normal allele) = Child: NN (normal genotype)
2. Father: N (normal allele) + Mother: n (albino allele) = Child: Nn (normal genotype)
3. Father: n (albino allele) + Mother: N (normal allele) = Child: Nn (normal genotype)
4. Father: n (albino allele) + Mother: n (albino allele) = Child: nn (albino genotype)
From these combinations, we see that there are three out of four possibilities that result in a child with the normal genotype (NN or Nn).
Therefore, the probability of the next child being normal for pigment is 3/4 or 75%.