Question:

A dihybrid test cross yielding a result of 1 : 1 : 1 : 1 ratio is indicative of

Updated On: Apr 18, 2024
  • Homozygous condition of the $F_1$ dihybrid
  • 4 different types of gametes produced by the $F_1$ dihybrid
  • 4 different types of gametes produced by the $P_1$ parent
  • 4 different types of $F_1$ generation dihybrids
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The Correct Option is B

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Answer (b) 4 different types of gametes produced by the $F_1$ dihybrid
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Explanation:

  • Gregor Johan Mendel developed a genetic tool known as test cross which is used to determine the genotype (homozygous or heterozygous) of dominant characters.
  • Individuals bearing identical alleles are called homozygous and those bearing different alleles are called heterozygous.
  • Another term known as ‘two-gene test cross’, is a type of testcross where two types of genes or phenotypic characters are studied.
  • Only two of the dominant characters among different characters of test individuals are considered. The phenotypic traits of the F1 generations are examined when a test person with two chosen dominant phenotypic traits is crossed with double recessive parents.
  • In a dihybrid test cross, if the test individual is heterozygous, a 1:1:1:1 phenotypic ratio is obtained.
  • For example, a red flower tall plant (dominant) is crossed with a yellow flower dwarf plant (recessive). In this case, the yellow flower dwarf plant is always homozygous (rrtt), but the red flower tall plant can be either homozygous (RRTT) or heterozygous (RrTt).
A dihybrid test cross yielding a result
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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.