Question

The kernel color in wheat is a continuous trait determined by two additive genes, each with two alleles, that equally contribute to kernel color determination. The red kernels are determined by two genes and two dominant alleles (R1R1R2R2), and white kernels are determined by two recessive alleles at the same two genes (r1r1r2r2). The duplicate dominant alleles R1 and R2 contribute equally to kernel color and cumulatively control the intensity of the red kernel phenotype. Both these alleles are dominant over the recessive white alleles r1 and r2. A true breeding red plant and true breeding white plant are crossed, and the resulting F1 progeny are selfed.

What is the expected phenotypic ratio of the kernel progeny of the F2 offspring?
Draw out your Punnett square. Indicate the doses (of red color) of each genotype. This will be a 4 x 4 Punnett similar to what you've done in the past for a dihybrid cross (bonus up to 1.5 pts)
Create a frequency distribution (by hand or spreadsheet) showing dosage on the X axis and frequency on the Y axis (bonus up to 1.5 pts)

Answer 1

Phenotypic ratio: 1:4:6:4:1

Punnett square: Below in the explanation box

Frequency distribution: In the attached files

Step-by-step explanation:

Available data:

• The kernel color in wheat is a continuous trait determined by two additive diallelic genes
• The red kernels are determined by two genes and two dominant alleles (R1R1R2R2)
• The white kernels are determined by two recessive alleles at the same two genes (r1r1r2r2)
• R1 and R2 alleles are dominant over r1 and r2, respectively

1st Cross: a true-breeding red plant with a true-breeding white plant

Parentals) R1R1R2R2 x r1r1r2r2

Gametes) R1R2, R1R2, R1R2, R1R2

r1r2, r1r2, r1r2, r1r2

F1) 100% R1r1R2r2

2nd Cross: F1 progeny are selfed

Parentals) R1r1R2r2 x R1r1R2r2

Gametes) R1R2, R1r2, r1R2, r1r2

R1R2, R1r2, r1R2, r1r2

Punnett square) R1R2 R1r2 r1R2 r1r2

R1R2 R1R1R2R2 R1R1R2r2 R1r1R2R2 R1r1R2r2

R1r2 R1R1R2r2 R1R1r2r2 R1r1R2R2 R1r1R2r2

r1R2 R1r1R2R2 R1r1R2r2 r1r1R2R2 r1r1R2r2

r1r2 R1r1R2r2 R1r1r2r2 r1r1R2r2 r1r1r2r2

F2) Genotype:

• 1/16 R1R1R2R2 (dark red)
• 2/16 R1R1R2r2 (red)
• 1/16 R1R1r2r2 (light red)
• 2/16 R1r1R2R2 (red)
• 4/16 R1r1R2r2 (light red)
• 2/16 R1r1r2r2 (very light red)
• 1/16 r1r1R2R2 (light red)
• 2/16r1r1R2r2 (very light red)
• 1/16 r1r1r2r2 (white)

Phenotype:

• 1/16 R1 R1 R2R2, dark red phenotype
• 4/16 R1r1R2R2 + R1R1Rr2, red phenotype
• 6/16 R1r1 R2r2 + r1r1R2R2 + R1R1r2r2, light red phenotype
• 4/16 R1r1 r2r2 + r1r1R2r2, very light red phenotype
• 1/16 r1r1r2r2, White phenotype phenotype

Phenotypic ratio: 1:4:6:4:1

Frequency table:

DOSAGE FREQUENCY

Dark red 1/16

Red 4/16

Light red 6/16

Very light red 4/16

White 1/16