Read the following passage carefully.
MONOHYBRID CROSS
The inheritance of flower color in the dog flower (Snapdragon or Antirrhinum sp.) can be understood by crossbreeding between true-breeding red-flowered (RR) and true-breeding white-flowered plants (rr). When they were crossed, $F_1$ (Rr) was pink. When $F_1$ was self-pollinated, the $F_2$ results were Red, Pink and White. Here the genotype ratios were exactly as expected, but the phenotype ratios have been changed. What happened was that R was not completely dominant over r and this made it possible to distinguish Rr as pink from RR (Red) and rr (White).
What will be the percentage of progeny in $F_1$ generation when RR (red flowered plant) is crossed with rr (white flowered plant) in the above passage?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → 100% Rr
Parent plants:
We are crossing:
- RR (red-flowered, because R = dominant allele)
- rr (white-flowered, because r = recessive allele
Gamete formation :
- The RR parent can produce only R gametes (since both alleles are R).
- The rr parent can produce only r gametes (since both alleles are r).
Fertilization :
During fertilization:
-
R × r = Rr
Since this is the only possible combination, all offspring will be Rr
F1 generation result :
-
Genotype of F₁: 100% Rr
-
Phenotype of F₁: 100% Red flowers (because R is dominant).
Therefore, in the F₁ generation, 100% progeny will be Rr.