This set of Class 12 Biology Chapter 5 Multiple Choice Questions & Answers (MCQs) focuses on “Polygenic Inheritance”.
1. What kinds of traits were described by Mendel?
a) Contrasting traits
b) Alternative forms
c) Mixed forms
d) Opposite and recessive forms
Explanation: Through the experiments of pea conducted by Mendel, he described distinct contrasting traits such as flower colour which are either purple or white.
2. What are polygenic traits?
a) Traits controlled by a single gene
b) Traits not controlled by any genes
c) Traits controlled by two genes
d) Traits controlled by three or more genes
Explanation: Traits are the feature of a character by which we can distinguish organisms. Traits which are generally controlled by three or more genes are known as polygenic traits.
3. Which of the following is a classic example of polygenic inheritance?
a) Skin colour in humans
b) Blood groups
c) Flower colour in peas
d) Stem height in peas
Explanation: Skin colour in humans is a classic example of polygenic inheritance as this trait is controlled by three or more genes and we can see that this trait is not so distinct amongst the human population and is spread across a gradient.
4. In humans, only tall and short people exist.
Explanation: Height of humans is a polygenic trait and is therefore not limited to only tall and short people. Instead of two distinct alternative traits, a range of all the possible heights is present in a human population.
5. What are polygenes?
a) Genes involved in quantitative inheritance
b) Genes involved in the qualitative inheritance
c) Genes involved in multiple allelism
d) Multiple genes for a single trait
Explanation: Genes which are involved in quantitative inheritance are called as polygenes. In quantitative inheritance, each dominant allele expresses itself as a part of functional polypeptide and the full trait is shown when all the dominant alleles are present in an organism.
6. Which of the following scientists demonstrated the quantitative traits in wheat?
a) Ernst Haeckel
b) H. Nilsson-Ehle
d) Paul Vincent
Explanation: H. Nilsson-Ehle in 1908 and East in 1910 demonstrated the segregation and assortment of genes that controlled the quantitative traits, e.g., Kernel colour in wheat and corolla length in tobacco.
7. Which two varieties of wheat were crossed by H. Nilsson to study the kernel colour in wheat?
a) Red and black kernelled variety
b) Red and white kernelled variety
c) White and black kernelled variety
d) Black and blue kernelled variety
Explanation: In order to study the kernel colour of wheat, H. Nilsson crossed red kernelled variety with a white kernelled variety of wheat. He found out that the kernel colour in wheat is determined by AA and BB genes.
8. What was the ratio of F2 generation when red and white kernelled variety of wheat were crossed?
a) 1: 2: 1
b) 9: 3: 3: 1
c) 1: 4: 6: 4: 1
d) 3: 1
Explanation: The ratio of F2 generation when red and white kernelled wheat varieties were crossed was obtained as-1: 4: 6: 4: 1. Also, five different phenotypic classes were obtained.
9. Which of the following is not a phenotypic class of the F2 generation in wheat?
a) Extreme red
b) Deep red
Explanation: The five phenotypic classes obtained while crossing red and white kernelled wheat variety are: the extreme red, deep red, intermediate red, light red and white.
10. On which of the following factor, the degree of redness of progenies depend?
a) Number of dominant alleles
b) Number of recessive alleles
c) Number of contrasting traits
d) Number of phenotypic characters
Explanation: When we crossed a red and white kernelled variety of wheat, we saw that all the red kernels do not exhibit the same shade of redness. The degree of redness was found to depend upon the number of dominant alleles.
11. On how many loci the genes responsible for skin colour are present?
Explanation: The three pair of genes which determine the skin colour in humans are present at three different loci and each dominant allele of that gene is responsible for the amount of melanin pigment in the skin.
12. On which of the following factors, the amount of melanin produced depends?
a) Number of recessive alleles
b) Number of chromosomes present in an individual
c) Number of dominant genes
d) Number of loci present in DNA
Explanation: The amount of melanin produced in the skin of humans is always proportional to the number of dominant genes. The effect of all the genes that are responsible for the skin colour is additive.
13. Davenport showed that six pairs of genes are involved in controlling the skin colour in humans.
Explanation: Davenport was a scientist who demonstrated that six genes are involved in controlling the skin colour in human beings. He also showed that skin colour can only be studied in a population.
14. Which of the following curves can be a representation of the skin colour in a population?
a) Sigmoid curve
b) An ellipse
d) J-shaped curve
Explanation: We can study the frequency distribution of skin colour in the form of a bell-shaped normal distribution curve which is also represented by a Histogram.
15. Which of the following conclusions can be made by studying a histogram?
a) Extreme phenotypes are common
b) Intermediate phenotypes are more frequent
c) Intermediate phenotypes are rare
d) All phenotypes are present in equal amounts
Explanation: We can draw two conclusions by studying a histogram. These are that in a polygenic inheritance, the extreme phenotypes are rare and the intermediate ones are more frequent.
16. Which of the following is not an example of quantitative trait?
a) Cob length in maize
b) Height in humans
c) Human intelligence
d) Blood groups in humans
Explanation: Cob length in maize, height in humans, human intelligence, milk and meat production, height in humans and size, shape and number of seeds and fruits in plants are some of the common examples of quantitative traits.
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