Question

Assume that plant height and flower size in Four O'Clock plants display antogonistic phenotypes. Four O'Clock plants can be tall or short and the flowers can be large or small. Assume each trait is governed by alleles of a single gene and that each follows Mendel’s first and second laws. You start with two pure breeding strains, one that is tall with large flowers and a second that is short with small flowers. You cross these two strains to each other to generate F1 plants. You self-cross an F1 plant and grow 342 of the resulting seeds into plants. You find that 195 plants are short with large flowers, 62 plants are short with small flowers, 59 plants are tall with large flowers, and 26 plants are tall with small flowers.

Which of the following alleles are likely loss-of-function alleles? (Select 'Yes' or 'No' for each)

Yes No  The allele for tall plants
Yes No  The allele for short plants
Yes No  The allele for small flowers
Yes No  The allele for large flowers

Answer 1

Yes. The allele for tall plants

No. The allele for short plants

Yes. The allele for small flowers

No. The allele for large flowers.

This is because a loss of function allele will be inherited in a recessive manner and hence will be expressed in a homozygous state only. As a result the number of F2 progenies having a this particular phenotype will be the least (=26) and it corresponds to tall and small phenotype. Thus, these two would be loss of function alleles.