If two recessive lethal alleles come together, they will be expressed and lead to the offspring's death. Let the dominant allele be S and the recessive allele be s. Here, the two individuals are heterozygous for it. So when they mate:
S s
S SS Ss
s Ss ss
1/4 have homozygous fominant genotype (SS), 2/4 have heterozygous genotype (Ss) and 1/4 have homozygous recessive (ss) genotype. Since 1/4 offspring have ss genotype, they will die. Hence, the usual 1:2:1 ratio has been modified here to only 1:2:0
The green colour of the unripe fruit is due largely to the presence of chlorophylls, and the development of different colours during ripening is due to the disappearance of these pigments and the synthesis of carotenoids.
