Test: Principles of Inheritance and Variation - NEET MCQ

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.

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 ture 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

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

heterozygous and recessive individuals are obtained in 1 : 1 ratio.

According to Mendelian inheritance, genes come in different varieties called alleles. Somatic cells contain 2 alleles with one allele provided by each parent of an organism.

Both the characters appear during the formation of F₂-generation, so no blending occurs.

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

genetic recombination. 8. (c) 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.

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.

Back cross is a cross of F₁ hybrid with either of the two parents. When F₁ offsprings are crossed with the dominant parents, all the F₂ generation offsprings develop dominant character. On the other hand, when F₁ hybrids are crossed with recessive parent, individuals with both the phenotypes appear in equal proportions. Crossing of F₁ individual with dominant phenotype with its homozygous recessive parent is called test cross. It is used to determine whether the individuals exhibiting dominant characters are homozygous or heterozygous

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.

F₂ phenotypic and genotypic ratio in monohybrid cross involving incomplete dominance is

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

In Mirabilis jalapa (four o'clock) have two types, of flower colour in pure state: red and white. When the two types of plants are crossed, the hybrid or plants of F₁ generation produce pink flowers. If the latter are selfed, the plants of F2 generation are of three types-red, pink and white flowered in the ratio of 1 : 2 : 1. Due to incomplete dominance of red (dominant) over white (recessive), the pink colour apparently appears. Thus, pink is differentiated from red and white.

In the ABO system, consists four blood groups A, B, AB and O. ABO blood groups are controlled by gene I. The gene has three alleles I^A, I^B and i. This phenomenon is known as multiple allelism. I^A and I^B are completely dominant over i. When I^A and I^B are present together, they both express themselves and produce AB blood group. This phenomenon is known as codominance.

The law of independent assortment states that two factors of each character separate or assort independent of the factors of other characters at the time of gamete formation and get randomly rearranged in the offspring producing both parental and traits of new combinations. The principle of law of independent assortment is applicable to only those factors or genes that are either located distantly on the same chromosome or occur on different chromosomes. Actually, a chromosome bears hundred of genes. All the genes of factors present on a chromosome are inherited together except when crossing over takes place.

Fruit colour of summer squash (Cucurbita pepo) is governed by a gene that produces yellow colour in dominant state (Y) and green colour in recessive state (YY). There is a non-pigment forming epistatic gene that in dominant state (W-_ produces white colour (W-Y-, W- yy) while in recessive state it allows the yellow (wwY-_ and green (wwyy) expression. This shows dominant epistasis where a dominant epistatic allele suppresses the expression of a non allellic gene whether the latter is dominant or recessive.

When two alleles for trait are equally expressed with neither being recessive or dominant, is known as codominance. As for example– A person with type AB blood, that means both A and B alleles are equally expressed.

In ABO blood group system, the classification of human blood is based on the inherited properties of red blood cells (erythrocytes) as determined by the presence or absence of the antigens A and B, which are carried on the surface of the red cells. One parent with A and another with B can produce a child with A, B, AB or O blood types.

During Anaphase of meiosis I, the two chromosome pairs can align at the metaphase plate independently of each other. Sutton and Boveri argued that the pairing and separation of a pair of chromosomes would lead to the segregation of a pair of factors they carried. Thus, both assertion and reason are true and reason is the correct explanation of assertion