Question

In Antirrhinum, when a cross is made between red and white flowers all resultant progenies are
(a) Red
(b) Pink
(C) White
(d) Red and white in equal numbers

Answer 1

Hint: Antirrhinum majus exhibits a special type of inheritance phenomenon where neither of the alleles for a particular trait is completely dominant over each other. A special effect of blending can be observed in the offsprings.

Complete answer:
Antirrhinum is a flowering plant species that is locally known as Snapdragon. This is due to the resemblance of the fruit from the flower to the mouth of a dragon. Normally, two types of flowers are borne by the plant- pure red and pure white though an intermediate version of the flower i.s. pink has also been observed. The color of the flower is controlled by a combination of two alleles. When a cross is made between two purebreds i.e dominant red flower-bearing plant with recessive white-bearing plant, all the progeny are hybrids i.e they all bear pink-colored flowers. Neither of the flowers resembles that of their parents.

Additional Information: -When the hybrids or the $F_1$ generation are self-pollinated, their offsprings in $F_2$ generation plants show the presence of red flowers, pink flowers, and white flowers in the ratio 1:2:1 i.e. RR:Rr:rr.
-Such type of inheritance is identified as incomplete dominance, wherein, neither of the alleles is expressed fully, and the blending of characters occurs, producing an intermediate end product.
-The homozygotes i.e RR or rr produce distinct red and white flowers respectively while the heterozygotes i.e Rr will produce pink flowers.
-As neither of the alleles i.e R or r is dominant over each other, masking of dominant allele over recessive allele doesn’t take place.
So, the correct answer is ‘Pink.’

Note: Incomplete dominance is different from the traditional phenomenon of complete dominance wherein in a heterozygous condition, the dominant allele completely masks the expression of the recessive allele. Thus, a recessive allele can only be expressed when it exists in a homozygous condition.
-Incomplete dominance is also observed in Mirabilis jalapa as shown in the diagram.