Twenty-four years have passed. Your baby is now an adult and has married someone

Question

Twenty-four years have passed. Your baby is now an adult and has married someone who's heterozygous for freckles. What is the probability that they'll have a child with freckles?

The first step in calculating the probability of freckles is to determine the alleles carried by the sperm and eggs of this couple. As you know, alleles separate in meiosis, so each sperm and each egg has only one allele from each homologous pair.

Your child's genotype for the freckle trait ________ __________.

1. A Punnett Square is a convenient way to visualize the different combinations of alleles that might occur during fertilization.
2. The spouse's alleles have been entered on the top row of the Punnett Square. Enter the alleles for your child along the left side of the square.

3. Using the Punnett Square as a guide, fill in the boxes by carrying the alleles down from the top and across (from left to right). Each box in the Punnett Square represents a 25% probability of having a baby with that specific genotype. What's the probability that this couple will have a child with freckles? ___________

Explanation / Answer

Freckles is caused by an autosomal dominant inheritance. Means, the individuals with the genotype FF or Ff wxhibit the phenotype of freckles, and recessive(ff) are normal.

Suppose, if the child's genotype for Freckles is recessive (ff),

Cross between a normal male (ff) and heterozygous female (Ff) will have the offpsring with following genotypes.

Ff* ff = Ff, ff, fF, ff. (the probability that this couple will have a child with freckles is, 1/2)

If,  if the child's genotype for Freckles is heterozygous (Ff), cross between a normal male (Ff) and heterozygous female (Ff) will have the offpsring with following genotypes.

Ff* Ff = FF, Ff, fF, ff. (the probability that this couple will have a child with freckles is, 3/4)

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