Question

Alleles of the gene that determines seed coat patterns in lentils can be organized in a dominance series: marbled > spotted = dotted (codominant alleles) > clear. A lentil plant homozygous for the marbled seed coat pattern allele was crossed to one homozygous for the spotted pattern allele. In another cross, a homozygous dotted lentil plant was crossed to one homozygous for clear. An F1 plant from the first cross was then mated to an F1 plant from the second cross. a. What phenotypes in what proportions are expected from this mating between the two F1 types? b. What are the expected phenotypes of the F1 plants from the two original parental crosses?

Answer 1

Answer:

• two types of cross are given,

1. marbled and spotted

here, marbled is dominant (MM) ; spotted is co-dominant (Ss)

in F1 generation → MS (marbled spotted coat)

    2. dotted and clear

here, dotted is co-dominant (Dd) ; clear is recessive (dd)

in F1 generation → Dd (clear background with dotted coat)

if     MS × Dd , then, it will give,

25% spotted and dotted ( as both are co-dominant {Ss=Dd}) : 50% marbled (as marbled is dominant{ MM}) : 25% spotted ( as spotted {Dd} is co-dominant and clear {dd} is recessive)

a. 25% spotted dotted: 50% marbled: 25% spotted

• expected phenotypes from F1 is  →

MS (marbled)- as marbled is the most dominant among all, it won't let spotted to be expressed.

and Dd - as clear is recessive only dotted will be expressed.

b.marbled and dotted.