Question

1)Rice yield is a quantitative trait. Imagine that rice yield is controlled by four additive allleles, A, B, C, and D.

Come up with an example cross of two different strains of rice that each produce an intermediate yield, and that when crossed, produce progeny that are also intermediate.

2) Rice yield is a quantitative trait. Imagine that rice yield is controlled by four additive allleles, A, B, C, and D.

Next, come up with an example cross of two different strains of rice that each produce an intermediate yield, but that when crossed, produce progeny that range from below average (but not lowest) yield to above average (but not highest) yield.

Answer 1

Given that the rice yield trait is controlled by four additive alleles namely, A , B, C, and D.

The genotype for maximum and minimum rice yield would be AABBCCDD and aabbccdd, respectively.

The genotype for intermediate yield would have 4 additive alleles, for example, AaBbCcDd, AABBccdd, AAbbCCdd, etc.

Part 1:

We need to cross two rice that each produce an intermediate yield, and that when crossed, produce progeny that are also intermediate. That is, both F1 and F2 should have 4 additive allels. We can design such a cross as follows:

Parents : AAbbccDD × AAbbccDD

Gametes from parents:

AbcD × AbcD

The cross can be shown as :

	AbcD
AbcD	AAbbccDD

F1: AAbbccDD ( has 4 additive alleles, and is thus intermediate).

F1 × F1 cross:

AAbbccDD × AAbbccDD

The cross would be similar to the parental cross, and thus,

F2 : AAbbccDD (intermediate).

Part 2:

We need to cross two different strains of rice that each produce an intermediate yield, but that when crossed, produce progeny that range from below average (but not lowest) yield to above average (but not highest) yield.

This means that F2 cannot be aabbccdd or AABBCCDD. It have have any other genotype.

One possible cross for the given condition :

Parents: AABBccDD × AAbbccdd

Gametes: ABcD × Abcd

F1: AABbccDd (intermediate, has 4 additive alleles).

F1 × F1: AABbccDd

Gametes from each F1 individual:

ABcD, ABcd, AbcD, and Abcd.

Note that in F2 the number of dominant alleles varies from 2 to 6 in an individual, as per required in the question.

(Apart from the crosses designed above, we can design more such crosses with different genotype as well.)