CBSE Class 10 Biology Heredity and Evolution MCQs Set 24

Answer: (d) Not applicable when the genes are on the same chromosome

Explanation:
1. Independent assortment holds for genes on different chromosomes.
2. Genes on the same chromosome are linked and tend to be inherited together.

Teacher's Note:
1. This is why it does not hold for linked genes.
2. Mendel's pea traits were on different chromosomes.

Answer: (c) Law of segregation

Explanation:
1. The recessive allele hidden in the F1 reappears in F2 because the alleles separate during gamete formation.
2. This is the law of segregation.

Teacher's Note:
1. The ratio is 3 tall : 1 dwarf.
2. The alleles do not blend.

Answer: (a) 50% will be tall with red fruit

Explanation:
1. RR x rr gives all Rr (red fruit).
2. Tt x tt gives 50% Tt (tall) and 50% tt (short).
3. So 50% are tall with red fruit.

Teacher's Note:
1. Work out each gene separately and then combine.
2. A cross with a double recessive is a test cross.

Answer: (a) A recessive trait can be expressed only in the homozygous condition

Explanation:
1. A recessive allele is masked by a dominant allele in the heterozygote.
2. It shows only when both alleles are recessive.

Teacher's Note:
1. A dominant allele shows in both homozygous and heterozygous condition.
2. Example: dwarfness appears only in tt.

Answer: (b) Independent assortment

Explanation:
1. A dihybrid cross studies two traits together.
2. It showed that the two pairs of alleles assort independently.

Teacher's Note:
1. The F2 phenotypic ratio is 9 : 3 : 3 : 1.
2. Mendel crossed round yellow and wrinkled green seeds.

Answer: (d) 50 : 50

Explanation:
1. Yy x yy gives 1 Yy (yellow) : 1 yy (green).
2. So the ratio is 50 : 50.

Teacher's Note:
1. This is a test cross.
2. A 3 : 1 ratio comes from Yy x Yy.

Answer: (d) They occupy different loci on the same chromosome

Explanation:
1. Alleles are alternative forms of a gene and occupy the same locus on homologous chromosomes.
2. They do not occupy different loci.

Teacher's Note:
1. Multiple alleles exist, as in blood groups.
2. Incomplete dominance gives an intermediate trait.

Answer: (a) Alleles

Explanation:
1. Alternative forms of a gene are called alleles.
2. Example: T and t for height.

Teacher's Note:
1. An individual with two different alleles is a heterozygote.
2. The alleles are at the same position on homologous chromosomes.

Answer: (a) Two X chromosomes

Explanation:
1. A zygote with XX develops into a female.
2. XY develops into a male.

Teacher's Note:
1. The father's sperm decides the sex of the child.
2. The mother always gives an X chromosome.

Answer: (d) Haeckel

Explanation:
1. Ernst Haeckel proposed the biogenetic law that the development of an individual repeats the evolutionary history of its race.
2. It is called the recapitulation theory.

Teacher's Note:
1. Ontogeny is development of the individual.
2. Phylogeny is evolutionary history.

Answer: (c) Lamarck

Explanation:
1. Lamarck proposed the theory of use and disuse of organs.
2. He also said that acquired characters are inherited.

Teacher's Note:
1. Example: his giraffe stretching its neck.
2. Weismann disproved it by cutting mouse tails.

Answer: (d) Darwinism

Explanation:
1. These ideas are part of Darwin's theory of natural selection.
2. Organisms better suited to the environment survive and reproduce.

Teacher's Note:
1. Variation is the raw material of selection.
2. Wallace also proposed natural selection.

Answer: (b) (i)-P, (ii)-M, (iii)-N, (iv)-O

Explanation:
1. Darwin proposed natural selection, Oparin the chemical origin of life (abiogenesis), Lamarck use and disuse, and Wegener continental drift.
2. This gives the second pairing.

Teacher's Note:
1. Oparin and Haldane gave the origin-of-life theory.
2. Alfred Wegener proposed continental drift.

Answer: (b) Small populations

Explanation:
1. Genetic drift is the random change in gene frequency, and its effect is strong in small populations.
2. In large populations, chance effects average out.

Teacher's Note:
1. Chance events can remove an allele completely.
2. It is a cause of evolution besides selection.

Answer: (d) All of the above

Explanation:
1. Mutations are sudden changes in the DNA, genes or chromosomes.
2. All of these can be called causes of mutation.

Teacher's Note:
1. Mutations give new variations.
2. Radiation and chemicals can cause them.

Answer: (a) Similar in origin, with similar or dissimilar functions

Explanation:
1. Homologous organs have the same basic structure and origin but may perform different functions.
2. This points to a common ancestor.

Teacher's Note:
1. Analogous organs have different origin but the same function.
2. The forelimbs of vertebrates are an example.

Answer: (c) Nail of man and claw of cat

Explanation:
1. Human nails and cat claws have the same origin.
2. Ginger is a stem and sweet potato a root, so they are analogous.

Teacher's Note:
1. The wings of bird and butterfly have different origins.
2. Homology shows common ancestry.

Answer: (a) Divergent evolution

Explanation:
1. Divergent evolution produces different species from a common ancestor in different environments.
2. Homologous organs are its result.

Teacher's Note:
1. Convergent evolution gives similar traits in unrelated groups.
2. Darwin's finches are an example.

Answer: (b) Analogous organs

Explanation:
1. Insect wings are different in origin from the wings of birds and bats.
2. So the three wings are analogous.

Teacher's Note:
1. Only the bird and bat wings are homologous (modified forelimbs).
2. Analogy is based on function.

Answer: (c) Radish and carrot

Explanation:
1. Carrot and radish are both modified roots, so they have the same origin.
2. Potato is a stem and tomato is a fruit.

Teacher's Note:
1. Homologous means the same origin.
2. Carrot and radish both store food in roots.

Answer: (a) The tendril of a pea plant and the spine of a cactus are homologous

Explanation:
1. Both the pea tendril and the cactus spine are modified leaves, so they are homologous.
2. Bird and insect wings are analogous, and bird and bat wings are homologous.

Teacher's Note:
1. Different functions can arise from the same organ.
2. Check the origin, not the function.

Answer: (a) Coccyx and pinna muscles

Explanation:
1. The coccyx (tail bone) and the muscles that move the ear are reduced and useless in humans.
2. So they are vestigial.

Teacher's Note:
1. Vestigial organs were functional in ancestors.
2. The appendix is another example.

Answer: (d) Homologous organs

Explanation:
1. Both are modified stems and so have the same origin.
2. They are homologous organs with different functions.

Teacher's Note:
1. One protects and the other helps climbing.
2. This is divergent evolution.

Answer: (a) Sedimentary rocks

Explanation:
1. Sedimentary rocks form in layers from sediments that can bury dead organisms.
2. The heat of igneous and metamorphic rocks destroys fossils.

Teacher's Note:
1. Layers lower down are older.
2. Fossils give evidence of evolution.

Answer: (b) The extinction of the organism occurred thousands of years ago

Explanation:
1. Deeper layers are older.
2. So an organism found deep in the earth died out a long time ago.

Teacher's Note:
1. Upper layers hold more recent fossils.
2. Rock layers are like pages of a history book.

Answer: (b) Quantity of radioactive carbon compound

Explanation:
1. Radioactive carbon (C-14) decays at a known rate.
2. Measuring how much remains gives the age of the fossil.

Teacher's Note:
1. This is called carbon dating.
2. It is used for fairly recent fossils.

Answer: (a) All variations in a species have an equal chance of survival

Explanation:
1. Some variations help survival and others do not, so they do not have equal chances.
2. The other statements are true.

Teacher's Note:
1. Variation is greater in sexual reproduction.
2. Natural selection acts on useful variations.

Answer: (d) Birds have evolved from reptiles

Explanation:
1. Feathered dinosaurs are reptiles, and feathers first had another use like warmth.
2. Later they were used for flight, so birds evolved from reptiles.

Teacher's Note:
1. This is a link between reptiles and birds.
2. It shows that a structure can gain a new function.

Answer: (b) Anthropology

Explanation:
1. Anthropology is the study of humans, including human evolution.
2. Palaeontology deals with fossils in general.

Teacher's Note:
1. Fossil hominids are studied by palaeoanthropologists.
2. Mammalogy studies mammals.

Answer: (b) Africa

Explanation:
1. Fossil evidence shows that early humans arose in Africa.
2. They later spread to other continents.

Teacher's Note:
1. Homo sapiens originated about 300,000 years ago.
2. Many early hominid fossils were found in Africa.