In chickens the dominant allele cr produces the creeper phenotype (having extremely short legs). however, the creeper allele is lethal in the homozygous condition. the homozygous recessive genotype results in a normal individual. if two creepers are mated, what will be the phenotypic ratio among the living offspring?

Let us denote the dominant cr allele with 'C' and the recessive cr with 'c'. The heterozygous creeper allele will be Cc. When two creepers mate the cross gets denoted by Cc x Cc. The resultant progeny will have the genotypes CC, 2 x Cc and cc . The cc are homozygous recessive for cr, they will be normal individuals and Cc are the creepers with short legs. The homozygous dominant allele CC will be of the lethal kind. Therefore, the phenotypic ratio will be 1:2:1 where 3 will survive (colored green) and 1 will die (colored red).