The flowers of Japanese morning glory may be either blue, scarlet, or purple. Wh
ID: 93763 • Letter: T
Question
The flowers of Japanese morning glory may be either blue, scarlet, or purple. When a true-breeding blue strain is crossed with a true-breeding scarlet strain the F_1 generation is all blue. When the F_1 generation is self-crossed, the F2 generation is: 9/16 blue 6/16 purple 1/16 scarlet Provide a genetic model to explanation these results. Create and define the necessary gene or genes and genetic symbols for your model and then, on the diagram of the cross below, label all of the groups with their genotype according to your model. Explain how the genes work to give the observed results.Explanation / Answer
Let us suppose,
The blue color is controlled by two dominant genes (A and B) and scarlet color is controlled by two recessive genes (a and b).
A cross between true-breeding blue and true-breeding scarlet strain, the F1 generation is all blue.
Parents: AABB (true-breeding blue) X aabb (true-breeding scarlet)
Gametes: AB ab
Offsprings: AaBb
F1 generation: ( blue color flowers as dominant allele A and B masks the effect of recessive allele a and b)
In F2 generation,
Parents: AaBb X AaBb
Gametes: AB, Ab, aB, ab AB, Ab, aB, ab
A Punnett square is drawn to find out the offsprings produced:
AaBB (blue)
AaBb (blue)
So, it has been cleared from the Punnett square that when dominant alleles are present at both gene pairs (A_B_), the flower color is blue. and when both are homozygous recessive (aabb), the color is scarlet. The purple flower color may be caused by dominant alleles at either one of two separate gene pairs, A_bb or aaB_.
Therefore, F2 progeny produced 9/16 blue, 6/16 purple and 1/16 scarlet and thus the phenotypic ratio is 9:6:1
It is an example of polymeric gene interaction, also called as duplicate genes with cumulative effect. In this interaction, when two independent dominant genes present individually in homozygous or heterozygous condition show similar phenotypic effect i.e purple color but when present together, they produce a cumulative effect i.e blue color.
AaBB (blue)
AaBb (blue)
Ab AABb (blue) AAbb (purple) AaBb (blue) Aabb (purple) aB AaBB (blue) AaBb (blue) aaBB (purple) aaBb (purple) ab AaBb (blue) Aabb (purple) aaBb (purple) aabb (scarlet)