Which of the following is the correct definition of a recessive allele?

• A. An allele expressed only if two copies are present in the phenotype.
• B. An allele expressed even if only one copy is present in the phenotype.
• C. An allele that is only inherited on the Y chromosome.
• D. An allele that prevents a dominant allele from being expressed.

A man who is heterozygous for a widow’s peak ($Ww$) and a woman with a straight hairline ($ww$) have a child. Determine the probability that the child will have a straight hairline.

Calculate the probability that their next child will be a boy with a straight hairline. Use the relation: $probability\; of\; a\; boy\; with\; a\; straight\; hairline=probability\; of\; straight\; hairline\times probability\; of\; being\; a\; boy$