Question:

When red and white flowered Mirabilis plants are crossed all pink flowers are seen in F generation. When F progeny is selfed, the expected phenotypic and genotypic ratios are

Updated On: Aug 1, 2022

1:2:1 and 3:1:1
3:1 and 1:2:1
1:2:1 and 1:2:1
1:1 and 1:1:1

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The Correct Option is C

Solution and Explanation

Sometimes two genes of allelomorphic pair do not show dominant-recessive relationship, but when present together, they show intermediate trait or incomplete dominance. Incomplete dominance is not blending inheritance because parental characters reappear in F generation. In Mirabilis jalapa, there are two types of pure breeding plants, red flowered and white flowered. On crossing them the F plants or hybrids possess pink flowers. On selfing them, F generation has plants in the ratio of 1 red : 2 pink : 1 white flowered plants with phenotypic ratio being same as genotypic ratio. Genotypic ratio = 1RR : 2Rr : 1rr Phenotypic ratio = 1 Red : 2 Pink : 1 White Both genotypic ratio and phenotypic ratio are same, i.e., 1 : 2 : 1.

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Concepts Used:

Principles of Inheritance and Variation - Mutation

A Mutation is a change in the sequence of our DNA base pairs caused by numerous environmental stimuli such as UV light or mistakes during DNA replication. Germline mutations take place in the eggs and sperm and can be passed onto offspring, whereas somatic mutations take place in body cells and are not passed on.

Types of Mutations

There are three types of mutations, which are as follows:

Silent mutation

It refers to any change in DNA sequence that has no effect on the amino acid sequence in a protein or the functions that a protein performs. There is no phenotypic indication that a mutation has occurred.

Nonsense mutation

When there is a change in the sequence of base pairs due to a point mutation, that results in a stop codon. This leads to a protein that is either shortened or non-functional.

Missense mutation

A missense mutation occurs when a point mutation causes a change in the codon, which then codes for another amino acid.

The mutation is caused by the following factors:

Internal Causes

When DNA copies incorrectly, the majority of mutations occur. Evolution occurs as a result of all of these mutations. DNA makes a copy of itself during cell division. When a copy of DNA isn't flawless, it's called a mutation since it differs somewhat from the original DNA.

External Causes

When certain chemicals or radiations are used to break down DNA, it causes the DNA to break down. The thymine dimers are broken by UV radiation, resulting in altered DNA.