Due to three different types of allele I_A, I_B, i in blood group, it shows multiple allelism.

Backcross is cro ss which is p e rfo rm ed between hybrid and one of its parents. In test cross, the individual is crossed with recessive parent. It is called a test cross, because it is used to test whether an individual is homozygous or heterozygous (hybrid).

In the monohybrid test cross progeny both heterozygous and recessive individuals are obtained in 1 : 1 ratio.

Complementary genes are those non-allelic genes which independently show a similar effect but produces a new trait when present together in the dominant form. W. Bateson and R.C. Punnett observed that, when two white flowered varieties of sweet pea, Lathyrus odoratus were crossed, F₁ progeny had coloured flowers. When F₂ progeny obtained from F₁ was classified, plants with coloured flowers and those with white flowers were obtained in 9 : 7 ratio. The two dominants are brought together in F₁ generation and therefore coloured flowers are produced.

Meiosis is the process by which gametes are formed and during this process only one variant of gene pass to the gamete.

According to Mendel's concept of inheritance, each gene had two alternative forms or allelomorphs, one being dominant and the other recessive. Practically, the wild form can mutate in several ways. The mutant form can also mutate once again to give rise to another mutant form. Therefore, a gene can have more than two allelomorphs. These allelomorphs make a series of multiple alleles.

An allele is an alternative form of a gene one member of a pair that is located at a specific position on a specific chromosome. Diploid organisms, for example, humans, have paired homologous chromosomes in their somatic cells, and these contain two copies of each gene.

Pure line is a strain of genetically pure true breeding individuals. Members of pure line are homozygous for one or more characters. In homozygous form both the factors express the same effect. These organisms are said to breed true. They are used for cross breeding in order to get the desired improvement in crops.

Correct option is D

Both Assertion and Reason are incorrect

A test cross is a cross involves the breeding of an individual with a phenotypically recessive individual, in order to determine the zygosity of the former by analyzing proportions of offspring phenotype and not the parent types. Back cross is the crossing of a hybrid with one of its parents or an individual genetically similar to its parent, in order to achieve offspring with a genetic identity which is closer to that of the parent. 

So, the correct answer is 'Both Assertion and Reason are incorrect'.

Mendel chose garden pea as plant material for his experiments, since it had the following advantages

(i) Well defined characters.

(ii) Bisexual flowers.

(iii) Predominantly self-fertilization.

(iv) Easy hybridization.

Besides these features, garden pea, being self-fertilized, had pure lines due to natural self-fertilization for a number of years. Therefore, any variety used was pure for the characters it carried. Mendel’s success was mainly based on the fact that he considered a single character at one time.

Both the parental traits of a character in F2 generation are expressed in the ratio of three dominant to one recessive. Whereas, in F1 generation only one of the parental traits is expressed and the other lies hidden or unexpressed. However, in the hybrid there is no mixing of two characters. At the time formation of gamete, two factors separate or segregate and passes into different gametes, that hence have one factor of a pair. During fertilization, gametes fuse randomly so that factors come together in new generation and freely express themselves.

On garden pea for many years mendel carried out hybridization experiments. He performed various types of cross breeding and then allowed the offspring for self breeding. He selected varieties and used pure lines of true breeding lines, i.e., they produce offspring resembling the parents. these lines show the stable trait inheritance and expression for several generations making them suitable for genetic studies.

Monohybrid cross is a cross between two organisms of a species which is made to study the inheritance of a single pair of alleles or factors of a character. Dominant character is one of a pair of alleles which can express itself whether present in homozygous or heterozygous state. In F1, generation, the generation of hybrids produced from a cross between the genetically different homozygous individuals called parents the progenies are heterozygous dominant.

True breeding lines have inheritance of pure characters for several generations.

Chromosomes carry gene that passes on the traits of parents to the offsprings during genetic recombination.