Final answer:
The likelihood of a couple producing children with thick, separate eyebrows is 0%, as both parents lack the separate eyebrows allele (S) necessary to express separated eyebrows.
Step-by-step explanation:
To determine the likelihood that two individuals will produce children with thick, separate eyebrows, we apply our understanding of Mendelian genetics. Broad thick eyebrows (B) are dominant to smaller slender eyebrows (b), and separated eyebrows (S) are dominant to joined eyebrows (s). The male with slender unibrow can be represented as bbss, being homozygous for both recessive traits, while the female with thick unibrow can be represented as Bbss, being heterozygous for the eyebrow thickness trait and homozygous for the joined eyebrow trait.
To find the likelihood that they will produce children with thick, separate eyebrows, we must look at the possible combinations of alleles. All offspring will inherit a b allele for eyebrow thickness from the father and either a B or b allele from the mother, resulting in 50% of the offspring (Bb) with thick eyebrows and 50% (bb) with slender eyebrows. Since both parents have at least one s allele for joined eyebrows, all offspring are guaranteed to inherit two s alleles (ss), resulting in 100% with a unibrow. Therefore, the likelihood of producing children with both thick and separate eyebrows is 0%, as neither parent has the separate eyebrows allele (S) to pass on.