This indicates that the expression of genes depends partly on environment.
Explanation:
The case shown in the question is showing a situation where there was a genetic interaction with the environment, resulting that gene expression depends in part on the environment.
Gene and environmental interactions are revealed by penetrance and expressiveness. Penetrance is the percentage of individuals with a given gene that have a phenotype linked to this gene, such as children and parents who have the same height. In cases of penetrance, a genotype may not express the expected phenotype due to gene influences and environmental effects, as happened to the couples' children shown in the question.
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