Question

A teacher wants his/her students to find the genotype of the Pea plants bearing purple coloured flowers in their school garden. Name and explain the cross that will make it possible.

Answer 1

Hint: The trait given to us is a single trait and the purple colour of flower is a character of the pea plant. The crosses which require two characters are known as dihybrid cross and the single character cross is called a monohybrid course.

Complete answer:
We all have studied about the crosses which were done by Mendel on the pea plants by taking in mind the seven different characters of the plant. One of them was the colour of the flower. We know that the purple colour of the flower was seen in most of the generations of the pea plant indicating that the purple colour is the dominant one and the recessive trait which was observed in the plant was white colour flowers. Now the question is teelin us to do the cross between one character of the plant and the cross which happens between one character is called a monohybrid cross. When Mendel crossed the pea plants, he also observed that there was a third colour of the flower which appeared in certain generations of the plant was the pink colour. He got the idea that this is an intermediate genotype where both the dominant and recessive traits allele were there leading to non expression of both the dominant and the recessive trait.
Now taking in mind the cross we can assume that the dominant trait which is purple colour can express itself only when the two dominant alleles are present in the gene. If both the alleles present in the gene are of recessive type then both the alleles are recessive ones. The third one which we talked about in the above paragraph was white colour and this was occurring only due to the presence of one dominant and one recessive allele. If we consider ‘w’ as recessive allele and ‘W’ as dominant allele then the genotype of purple colour flower is ‘WW’.

Note: We know that there are two types of crosses which are monohybrid and dihybrid cross, but there exist a third type of cross in which three different types of traits are taken into consideration and the cross is carried out having three different characters. The phenotype and the genotype ratio is also different in all the cases.