An individual with (naturally) curly hair and an individual with (naturally) straight hair mate; all of their offspring have (naturally) wavy hair. if an individual with wavy hair mates with an individual with straight hair, what is the probability that their child will have curly hair?

I believe the correct answer is 0

The parents who had children had wavy hair and straight hair. With the wavyhair parent having a dominant heterozygous H gene for curly hair from the first parent and a recessive h gene from the secod parent, having children with a mating partner who has homozygous hh for straight hair meant that half of the offsprings will have heteroygous wavy hair gene while the other half will have the homozygous straight hair gene.

Let Curly hair be: HH

Let Straight hair be: hh

Parental gametes = HH(curly hair) x hh(straight hair)

These 2 parents had offsprings as represented in the Punnet square below:

HH

h HhHh

h HhHh

Genotypic ratio of offsprings: 4Hh

Phenotypic ratio of offsprings: 4 Wavy hair.

One of the offsprings with wavy hair went ahead and had offsprings with an individual with straight hair. It is represented in the Punnet square below:

Let Straight hair be: hh

Let wavy hair be: Hh

Parental gametes = Hh(Wavy hair) x hh(straight hair)

Hh

h Hhhh

h Hhhh

Genotypic ratio of offsprings: 2Hh:2hh

Phenotypic ratio of offsprings: 2 Wavy hair: 2 straight hair

NOTE: None of the children had curly hair (HH)

The probability that the child will have curly hair (HH) = 0/4 hence the proalility is 0. None of the children were born with curly hair