Practice question

Fruit shape in Cucurbita pepo controlled by two non-allelic genes with cumulative duplicate effect produces modified ratio 9:6:1. Genotype A-B- with both dominant alleles yields disc shape due to combined action; genotypes A-bb and aaB- each carrying single dominant allele produce same intermediate spherical phenotype because either dominant alone gives spherical; genotype aabb double recessive yields long fruit. Combining two spherical classes 3+3 gives 6, resulting in 9 disc :6 spherical :1 long. This duplicate genes with cumulative effect illustrates non-epistatic interaction where dominants partially redundant but together novel.