Question

A study found that children with light-coloured eyes are likely to have parents with light-coloured eyes. On this basis, can we say anything about whether the light eye colour trait is dominant or recessive? Why or why not?

Answer 1

Hint: Recessive traits are seen when they are present in homozygous condition. In heterozygous condition, the dominant trait is seen. For the identification of dominant traits, the genotype should be known.

Complete step by step answer:
-According to laws of inheritance, the law of dominance states that when two homozygous organisms are crossed with a single pair of contrasting characters, the trait which is expressed in the first generation is called dominant and the character which is not expressed is called recessive.
-Eye colour is also a polygenic trait which is altered by multiple genes. The phenotype expressed is the cumulative effect of dominant alleles present. When both, the children and parents, have light eye colour then there must have been no dominant genes or one of two might be present.
-The genotype of the children are also known yet so it's not confirmed with homozygous condition or heterozygous condition. Thus, at least three generations are required for determining the dominant trait or recessive trait.If It was heterozygous, one should have a darker eye color gene (3:1) which is passed to the next generation. If it was homozygous, then it can be recessive only as there are no pure lines obtained of dominant genes.
-So, the genotype of parents and also three generation data is needed to confirm while only two generation data is provided.

Note:
The eye colour is an example of polygenes. The additive or cumulative effect is seen in dominant alleles.