Two parents who can see well and have wavy hair had their first child – blind and with straight hair.

Two parents who can see well and have wavy hair had their first child – blind and with straight hair. The second child saw well and had even hair. What is the likelihood that this family will have a blind child with wavy hair?

Since the parents have a child with traits that are not present in either of them, it should be concluded that these traits are recessive and that both parents carry recessive genes that cause them.

Let’s designate the gene for blindness as s, then the gene for normal vision will be S.

Let’s designate the gene for straight hair as p, then the gene for wavy hair will be P.

A blind child with straight hair is an sspp.

The heterozygous parents will be SsPp, they will both produce SP, sp, Sp and sP germ cells.

The offspring options possible for a given married couple will look like this:

children with normal vision and wavy hair (SSPP, 4 SsPp, 2 SsPP, 2 SSPp);

blind children with straight hair (sspp);

blind children with wavy hair (2 ssPp, ssPP);

children with smooth hair and normal vision (2 SSpp, Sspp).

The odds of having a blind baby with wavy hair would be 3 in 16, or 18.75%.

Answer: 18.75%.