Heredity & Evolution
NCERT Exemplar Problems
Question 13: Select the correct statement
- Tendril of a pea plant and phylloclade of Opuntia are homologous
- Tendril of a pea plant and phylloclade of Opuntia are analogous
- Wings of birds and limbs of lizards are analogous
- Wings of birds and wings of bat are homologous
Answer: (a) Tendril of a pea plant and phylloclade of Opuntia are homologous
Explanation: They are modified stems but serve different functions in different plants. We know that organs with similar origin/design are called homologous structures.
Question 14: If the fossil of an organism is found in the deeper layers of earth, then we can predict that
- the extinction of organism has occurred recently
- the extinction of organism has occurred thousands of years ago
- the fossil position in the layers of earth is not related to its time of extinction
- time of extinction cannot be determined
Answer: (b) the extinction of organism has occurred thousands of years ago
Explanation: Newer fossils are deposited in layers above older fossils.
Question 15: Which of the following statements is not true with respect to variation?
- All variations in a species have equal chance of survival
- Change in genetic composition results in variation
- Selection of variants by environmental factors forms the basis of evolutionary processes.
- Variation is minimum in asexual reproduction
Answer: (a) All variations in a species have equal chance of survival
Explanation: Useful variations stand a chance of survival because nature selects only the useful variations.
Question 16: A trait in an organism is influenced by
- paternal DNA only
- maternal DNA only
- both maternal and paternal DNA
- neither by paternal nor by maternal DNA
Answer: (c) both maternal and paternal DNA
Explanation: Both parents equally contribute to the DNA of an individual.
Question 17: Select the group which shares maximum number of common characters
- two individuals of a species
- two species of a genus
- two genera of a family
- two genera of two families
Answer: (a) two individuals of a species
Explanation: The lowest taxon shows the maximum number of common characters. Species is the lowest taxon.
Question 18: According to the evolutionary theory, formation of a new species is generally due to
- sudden creation by nature
- accumulation of variations over several generations
- clones formed during asexual reproduction
- movement of individuals from one habitat to another
Answer: (b) accumulation of variations over several generations
Explanation: Theory of sudden creation has long been disproved by scientists. It is the accumulation of variations over successive generations which results in origin of a new species.
Question 19: From the list given below, select the character which can be acquired but not inherited
- colour of eye
- colour of skin
- size of body
- nature of hair
Answer: (c) size of body
Explanation: Traits in other options are always inheritable traits.
Question 20: The two versions of a trait (character) which are brought in by the male and female gametes are situated on
- copies of the same chromosome
- two different chromosomes
- sex chromosomes
- any chromosome
Answer: (b) Two different chromosomes
Explanation: This obeys Mendel’s First Law of Inheritance.
Question 21: Select the statements that describe characteristics of genes
- genes are specific sequence of bases in a DNA molecule
- a gene does not code for proteins
- in individuals of a given species, a specific gene is located on a particular chromosome
- each chromosome has only one gene
- (i) and (ii)
- (i) and (iii)
- (i) and (iv)
- (ii) and (iv)
Answer: (b) (i) and (iii)
Explanation: A gene codes for a protein, and a chromosome can have many genes. So, statements (ii) and (iv) are incorrect.
Question 22: In peas, a pure tall plant (TT) is crossed with a short plant (tt). The ratio of pure tall plants to short plants in F2 is
- 1 : 3
- 3 : 1
- 1 : 1
- 2 : 1
Answer: (c) 1 : 1
Explanation: Following combinations of genotype emerge in F2 generation: TT (1), tt(1) and Tt (2). This shows that ratio of pure tall (TT) to pure short (tt) is 1:1.
Question 23: The number of pair (s) of sex chromosomes in the zygote of humans is
Answer: (a) One
Explanation: The sex chromosomes are in the 23rd pair.
Question 24: The theory of evolution of species by natural selection was given by
Answer: (b) Darwin
Question 25: Some dinosaurs had feathers although they could not fly but birds have feathers that help them to fly. In the context of evolution this means that
- reptiles have evolved from birds
- there is no evolutionary connection between reptiles and birds
- feathers are homologous structures in both the organisms
- birds have evolved from reptiles
Answer: (d) Birds have evolved from reptiles