CBSE Class 10 Biology Heredity and Evolution MCQs Set 06

Answer: (a) an extra 21st chromosome

Explanation:
1. Down's syndrome is trisomy 21: the person has 47 chromosomes with three copies of chromosome 21.

Teacher's Note:
1. It is caused by non-disjunction during gamete formation.
2. Klinefelter's syndrome is XXY.

Answer: (b) recessive one

Explanation:
1. In F₁ the dominant allele masks the recessive one.
2. In F₂ the recessive trait reappears in one quarter of the offspring.

Teacher's Note:
1. Mendel's monohybrid cross gives 3 : 1 in F₂.
2. The recessive appears only when two recessive alleles are together.

Answer: (c) a and b antibodies and no antigens

Explanation:
1. Group O red cells have neither A nor B antigen.
2. The plasma contains both anti-A and anti-B antibodies.

Teacher's Note:
1. Group AB has both antigens and no antibodies.
2. Group O is the universal donor for red cells.

Answer: (d) on different chromosomes

Explanation:
1. Genes on different chromosomes separate independently during meiosis.
2. Genes on the same chromosome tend to be inherited together (linkage).

Teacher's Note:
1. Mendel's pea characters lie on different chromosomes.
2. Linked genes violate independent assortment.

Answer: (a) 1

Explanation:
1. The F₂ ratio is 9 : 3 : 3 : 1.
2. Only one in 16 shows both recessive characters.

Teacher's Note:
1. Double recessive means homozygous recessive for both genes, e.g. rryy.
2. Use a 4 × 4 Punnett square.

Answer: (b) mutation

Explanation:
1. A mutation is a sudden, heritable change in the DNA or chromosomes of an organism.

Teacher's Note:
1. Mutations are the source of new alleles.
2. Radiation and some chemicals increase their rate.

Answer: (c) euploidy

Explanation:
1. Euploidy means a change in whole sets of chromosomes, such as 3n or 4n.
2. Aneuploidy is a gain or loss of single chromosomes.

Teacher's Note:
1. Polyploidy is a kind of euploidy.
2. Seedless watermelon is triploid.

Answer: (d) animal husbandry

Explanation:
1. Animal husbandry deals with the care and breeding of domestic animals to improve their products.

Teacher's Note:
1. Selective breeding and cross-breeding are its tools.
2. Veterinary science deals with animal diseases.

Answer: (a) leukaemia

Explanation:
1. Leukaemia is the uncontrolled multiplication of white blood cells.
2. Leucopenia is a fall and leucocytosis a rise in white cell count without cancer.

Teacher's Note:
1. The name means 'white blood'.
2. It is a cancer of blood-forming tissue.

Answer: (b) special creation

Explanation:
1. Special creation holds that each species was created separately by a divine act.

Teacher's Note:
1. Biogenesis means life comes only from life.
2. Chemical evolution is Oparin's idea.

Answer: (c) demography

Explanation:
1. Demography is the study of the size, structure and changes of human populations.

Teacher's Note:
1. Natality and mortality are factors it studies.
2. Emigration and immigration are movements of people.

Answer: (d) biogenesis

Explanation:
1. Pasteur's swan-neck flask experiment showed that microbes come only from pre-existing microbes.
2. This supported biogenesis and disproved spontaneous generation.

Teacher's Note:
1. Abiogenesis is the old idea of life from non-living matter.
2. Pasteur also developed pasteurisation.

Answer: (a) the nictitating membrane

Explanation:
1. The nictitating membrane is a small fold at the inner corner of the eye, a remnant of the third eyelid of other vertebrates.
2. The gall bladder, iris and pancreas are functional.

Teacher's Note:
1. Other human vestiges: appendix, wisdom teeth, ear muscles.
2. Vestigial organs are evidence of evolution.

Answer: (b) Archaeopteryx

Explanation:
1. Archaeopteryx had feathers and wings like birds and teeth, a long bony tail and clawed fingers like reptiles.
2. It is a connecting link between reptiles and birds.

Teacher's Note:
1. Connecting links show how groups are related.
2. Lungfish links fishes and amphibians.

Answer: (c) Python

Explanation:
1. Pythons have small spur-like remnants of hind limbs.
2. Cobras, sharks and eels have no trace of hind limbs.

Teacher's Note:
1. Remnants of limbs show descent from four-legged ancestors.
2. Whales also have vestigial hind-limb bones.

Answer: (d) Weismann

Explanation:
1. August Weismann cut off the tails of mice for 22 generations and the young still had tails.
2. This showed that acquired characters are not inherited.

Teacher's Note:
1. Lamarck's idea was use and disuse.
2. Darwin proposed natural selection.

Answer: (a) water vapour, ammonia, hydrogen and methane

Explanation:
1. Miller and Urey passed electric sparks through water vapour, methane, ammonia and hydrogen.
2. Amino acids formed, supporting Oparin's idea of chemical evolution.

Teacher's Note:
1. The atmosphere was assumed to have no free oxygen.
2. The sparks imitated lightning.

Answer: (b) natality, mortality and migration (all of these)

Explanation:
1. Births (natality) and immigration add individuals.
2. Deaths (mortality) and emigration remove them.

Teacher's Note:
1. Population change = births − deaths + immigration − emigration.
2. Malthus linked growth to food supply.

Answer: (c) a better developed brain and a differently shaped jaw

Explanation:
1. Humans have a larger brain, more developed senses and a smaller, differently shaped jaw.
2. Neither humans nor apes have tails, and both have a backbone.

Teacher's Note:
1. Brain size is the key difference.
2. Man and apes share a common ancestor.