Unattached earlobes is dominant to attached earlobes. Two parents, both with unattached earlobes, had a child with attached earlobes. What are the chances that their next child will have attached earlobes?

The correct option is B. 25%

It is given that unattached earlobes are dominant over attached earlobes. Let us consider the allele for unattached earlobe as E and the allele for attached earlobe as e.

If both the parents with unattached earlobes had a child with attached earlobes, that means both the parents must have the heterozygous genotype (Ee) for the character. It is the only reason, why the offspring can have attached earlobes getting recessive alleles (e) from both the parents.

Parents Ee X Ee

Gametes E/e E/e

F1 generation can be given in the form of a Punnett square:

Gametes	E	e
E	EE	Ee
e	Ee	ee

Therefore only one of the possible offspring has the genotype 'ee' specific for the recessive character of attached earlobes. One out of four possible offspring can have the character, which means a 25% chance is there for the offspring to have attached earlobes.

Final answer: There is a 25% chance that the next child will have attached earlobes.