Question

In Antirrhinum, two plants with pink flowers were hybridized. The F1 plants produced red, pink and white flowers in the proportion of 1 red,2 pink and 1 white. What could be the genotype of the two plants used for hybridization. Red flower colour is determined by RR, and white by rr genes?
A. rr
B. RR
C. Rr
D. rrrR

Answer 1

Hint: Mendel conducted artificial pollination or cross-pollination experiments using several true-breeding pea lines A true breeding line is one that having undergone continuous self-pollination, shows the stable trait inheritance and expression for several generations.

Complete Answer:
Mendel selected a total of 14 true-breeding pea plant varieties, such as the height of the stem whether tall or dwarf as pairs which were similar except for one character with contrasting traits. It means, Mendel selected 7 characters that are seed shape, seed colour, pod colour in pea plant for carrying out hybridization experiments and to study inheritance
Mendel crossed pea plants say for example stem height and cross tall and dwarf plants and got ration
3:1 but some inheritance differs from this ratio as:-
- After the law given by Mendel , a few cases were observed and seen where F1 phenotype is intermediate between dominant and recessive phenotype, it means F1 did not resemble either of the two parents and was in between the two.
- A most popular example of incomplete dominance is that of flower colour in Snapdragon (dog flower or Antirrhinum majus). True-breeding red-flowered plant (RR) was crossed with true breeding white flowered plants (rr). F1 offspring (Rr) had pink flowers.
- Here one allele is incompletely dominant over another so that intermediate phenotype is produced by F1 hybrid with respect to the parents. If the F1 is made to undergo self-pollination , the plants of F1 generation are of three types red (RR), pink (Rr) and white flowered (rr) in the ratio of 1: 2: 1. In heterozygous condition (Rr), the phenotypic effect of one allele is more pronounced than that of the other and mixing of both colours (red & white) results in the development of pink colour.

Hence, the required option is C that is Rr.

Note: Genes usually function or express themselves singly or individually. But many cases are known where two genes of the same allelic pair or genes of two or more different allelic pairs influence one another. This is called gene interaction and exception to mendelian arises due to this.