Question

What is the ratio of one pair of contrasting characters in F2 of a dihybrid cross?
A. \[5:3\]
B. \[3:1\]
C. \[1:1\]
D. \[1:2:2:4:1:2:1:2:1\]

Answer 1

Hint: A dihybrid cross is a cross between two individuals who differ in two features controlled by two separate genes. If both parents are homozygous for both genes, the offspring of the \[F1\] generation will be uniformly heterozygous for both genes and will have the dominant phenotype for both qualities. In the \[F2\] generation, self-pollination or crossing of these \[F1\] individuals will result in predictable genotype and phenotypic ratios. Deviations from these expected ratios could indicate that the two qualities are connected, or that one or both traits have a non-Mendelian inheritance mechanism.

Complete answer:
Option A: The contrasting character ratio in \[F2\] is \[1:2:1\]. Explanation: The genotype ratio in the second filial generation is \[1:2:1\]. A dihybrid cross is one that is created after two generations of crossing.
So, option A is not correct
Option B: The ratio for two sets of opposing characteristics in \[F2\] of a dihybrid cross is
\[9:3:3:1\]
The ratio becomes \[3:1\] for one pair of contrasting characters (such as seed form, which can be spherical or wrinkled).
This can be stated as follows:
Total number of plants with round seeds \[ = 9 + 3 = 12\] based on the dihybrid cross ratio.
\[3 + 1 = 4 = \] total number of plants with wrinkled seeds
Round: wrinkled \[ = 12:4 = 3:1\] as a result.
So, option B is correct
Option C: The phenotypic ratio is \[1:1:1:1\], which is a classic Mendelian ratio for a test cross in which alleles from two genes independently assort into gametes. It's a test that's used to figure out a parent's genotype.
So, option C is not correct
Option D: In \[F2\], the character contrast ratio is \[1:2:1\]. Explanation: In the second filial generation, the genotype ratio is \[1:2:1\]. After two generations of crossing, a dihybrid cross is generated.
So, option D is not correct.

So, option B is the correct answer

Note:
Mendel’s laws of inheritance-
1. Law of Dominance- It's also known as Mendel's first law of inheritance. Recessive traits refer to the repressed alleles, whereas dormant traits refer to the alleles that determine the phenotype.
2. Law of Segregation- The law of segregation states that during gamete formation, two copies of each genetic component separate, resulting in offspring inheriting one element from each parent. In other words, allele pairs separate during gamete formation and re-unite at random during fertilisation.
3. Law of Independent Assortment- The law of independent assortment, sometimes known as Mendel's second law of heredity, states that a pair of characteristics segregates independently of another pair during gamete development. Because the many hereditary variables assort separately, different traits have an equal chance of happening together.