Final answer:
Yes, it is possible for all children to have brown eyes if Teddy's mother is heterozygous for the eye color gene. The most likely scenario for brown-eyed parents producing a green-eyed child is that both are heterozygous, carrying an allele that can result in green eyes.
Step-by-step explanation:
In humans, eye color is a complex trait that involves multiple genes, and brown eyes are a dominant trait over blue eyes. Given that Teddy has brown eyes, with a mother with brown eyes and a father with blue eyes, a Punnett square can help predict the possible genotypes of their offspring. Since Teddy's father must have two recessive alleles (bb) because blue eyes are recessive, and all children have brown eyes, the mother must carry at least one dominant allele. Since all four children have brown eyes, the mother must be heterozygous (Bb), carrying one brown allele (dominant) and one blue allele (recessive), making it genetically possible for all children to have the phenotype of brown eyes.
If a couple with brown eyes produces a green-eyed child, it means the parents could be heterozygous and carry alleles that can produce green eyes in their children. The most likely answer is (b) both parents are heterozygous, having the green trait on the green-blue eye gene. This indicates that each parent carries one allele for brown eyes and one allele potentially contributing to green eyes, and when combined, there is a possibility for the phenotype of green eyes.