Biology MCQs for Class 12 with Answers Chapter 3 ( Inheritance and Variation )

Multiple choice questions.

1. Phenotypic ratio of incomplete
dominance in Mirabilis jalapa.
    a. 2 : 1 : 1.
    b. 1 : 2 : 1
    c. 3 : 1
    d. 2 : 2

Answer : b ( 1:2:1)
Explanation : In four o'clock plants (Mirabilis jalapa) we can Gross a plant with red flower petales with another with white petales, the offspring have pink flower petales. If these pink flowered F1 plants are crossed, the F2 plants appear in a ratio of 1:2:1, having red, pink or white petals, respectively.


2. In dihybrid cross, F2 generation offsprings show four different phenotypes while the genotypes are ................
    a. six
    b. nine
    c. eight
    d. sixteen

Answer : b ( nine )
Explanation : The two different phenotypes in the dihybrid cross are seed color and seed shape. One plant is homozygous for the dominant traits of yellow seed color (YY) and round seed shape (RR). The genotype can be expressed as (YYRR). ... The F2 progeny exhibits four different phenotypes and nine different genotypes.


3. A cross between an individual with unknown genotype for a trait with recessive plant for that trait is ..............
    a. back cross
    b. reciprocal cross
    c. monohybrid cross
    d. test cross

Answer : d ( Test cross )

Explanation : A cross between an individual with unknown genotype for a trait with recessive plant for that trait is test cross. - Test cross is cross between individual with unknown genotype and an individual with a phenotypically recessive individual.


4. When phenotypic and genotypic ratios are the same, then it is an example of ............
    a. incomplete dominance
    b. complete dominance
    c. Multiple alleles
    d. cytoplasmic inheritance

Answer : a ( Incomplete Dominance) Explanation : When phenotypic and genotypic ratio is the samethen it is an example of *incomplete dominance*. - Incomplete dominance is a form of intermediate inheritance in which one allele for a specific trait is not completely expressed over its paired allele.


5. If the centromere is situated near the end of the chromosome, the chromosome is called ................
    a. Metacentric
    b. Acrocentric
    c. Sub-Metacentric
    d. Telocentric

Answer: d (Telocentric)
Explanation: The centromere is situated at the tip of the chromosome it is called the telocentric chromosome.

The centromere is the position of a chromosome that joined a pair of sister chromatids. Position of the centromere in a chromosome classified the type chromosome.

6. Chromosomal theory of inheritance was proposed by ................
    a. Sutton and Boveri
    b. Watson and Crick
    c. Miller and Urey
    d. Oparin and Halden

Answer : a ( Sutton & Boveri ) 
Explanation : Theodor Boveri and Walter Sutton are the scientists credited with an extension of Mendel's laws, known as the chromosome theory of inheritance. In essence, this theory, which was developed in the early 1900s, explains what Mendel observed in his pea plants, otherwise known as the Boveri and Sutton chromosome theory.



7. If the genes are located in a chromosome as p-q-r-s-t, which of the following gene pairs will have least probability of being inherited together?
    a. p and q
    b. r and s
    c. s and t
    d. p and s
Answer : -

8. Find the mis match pair :
    a. Down’s syndrome = 44 + XY
    b. Turner’s syndrome = 44 + XO
    c. Klinefelter syndrome = 44 + XXY
    d. Super female = 44 + XXX

Answer : d (Super Female)


9. A colourblind man marries a woman, who is homozygous for normal colour vision ,the probability of their son being colourblind is
    a. 0%
    b. 25%
    c. 50%
    d. 100%

Answer : a (0)

Explanation : Colour blind man (XcY) with Normal homozygous woman (XX) → Son (XY) (normal vision) Son receives Y chromosome from father and X chromosomes from mother, hence he has zero probability of being colour-blind.