Question

An Ss x Ss mating is performed. If the phenotypic ratio of the progeny is 3 S- (_ indicates that the other allele is unknown) is 1 ss, then

- the S allele is dominant to the s allele
- The s allele is dominant to the S allele
- neither allele is dominant
- the relationship between the allele s cannot be determined

Answer 1

The S allele is dominant to the s allele. Individuals with both S and s alleles (Ss) will express the dominant phenotype, while individuals with two copies of the recessive s allele (ss) will exhibit the recessive phenotype.

Step-by-step explanation:

The phenotypic ratio of 3 S- to 1 ss in the progeny suggests that the S allele is dominant to the s allele. This means that individuals with both S and s alleles (Ss) will express the dominant phenotype, while individuals with two copies of the recessive s allele (ss) will exhibit the recessive phenotype.

For example, if we assume that the S allele codes for long stems and the s allele codes for short stems in pea plants, then 75% of the offspring from an Ss x ss mating would be expected to have long stems, while 25% would have short stems.

This conclusion is based on the principles of Mendelian genetics, where trait expression is determined by the interaction between alleles, and dominant alleles mask the expression of recessive alleles.