CBSE Class 10 Science Heredity and Evolution MCQs Set 09

Answer: (d) Variation

Explanation:
1. Differences between the offspring and their parents (and among the offspring) are called variations.
2. Inheritance is the passing of traits, and genetics is the study of heredity; neither names the differences. Hence the answer is variation.

Teacher's Note:
1. Heredity explains the similarities between parents and offspring.
2. Variation explains the differences, and both are studied together in this chapter.

Answer: (c) Variation

Explanation:
1. Differences in the characteristics of individuals of the same species are called variations.
2. Adaptation and evolution are different ideas, so variation is the answer.

Teacher's Note:
1. Variations arise from errors in DNA copying and from sexual reproduction.
2. They are the raw material for survival of a species in a changing environment.

Answer: (d) All of the above

Explanation:
1. Statement (a) is correct: traits are carried by genes on chromosomes.
2. Statement (b) is correct: the gene that expresses itself is dominant and the masked one is recessive.
3. Statement (c) is correct: one gene for each trait comes from each parent and the dominant one is expressed.
4. Hence all of the above are true.

Teacher's Note:
1. Each trait is controlled by a pair of genes, one from each parent.
2. The dominant gene decides the visible trait in a hybrid.

Answer: (d) None of the above

Explanation:
1. Eye colour, height and hair colour are all controlled by genes and can be inherited.
2. So there is no trait in (a), (b) or (c) that is free of gene control, and the answer is none of the above.

Teacher's Note:
1. Height is also influenced by nutrition, but its basic control is genetic.
2. In such questions check whether each option can be wrong before choosing 'none'.

Answer: (c) Size of body

Explanation:
1. Eye colour, skin colour and nature of hair are controlled by genes and inherited.
2. Body size depends on nutrition and environment during life, so it can be acquired but not inherited.

Teacher's Note:
1. Acquired traits are not passed to offspring.
2. Body size is an example because it can change with food and exercise.

Answer: (c) Brown eye colour

Explanation:
1. Hair colouring, acquired skills and scars are changes made during life and do not change the DNA of germ cells.
2. Brown eye colour is controlled by genes, so it is most likely to be inherited.

Teacher's Note:
1. Only genetic (inherited) traits pass to the next generation.
2. Acquired traits are not inherited.

Answer: (a) Mendel

Explanation:
1. Gregor Johann Mendel worked on garden pea plants and discovered the basic laws of inheritance.
2. He is therefore called the Father of Genetics.

Teacher's Note:
1. Robert Hooke discovered cells, Faraday worked in electricity and Newton in motion and gravitation.
2. Mendel's work was published in 1866.

Answer: (c) both maternal and paternal DNA

Explanation:
1. A child receives half of its genetic material from the father and half from the mother.
2. So each trait can be influenced by both maternal and paternal DNA.

Teacher's Note:
1. Each parent contributes one allele for every gene.
2. This is why children resemble both parents.

Answer: (c) allele

Explanation:
1. Contrasting forms of a character, such as tall and dwarf, are carried by alternative forms of a gene.
2. These alternative forms of a gene are called alleles.

Teacher's Note:
1. Phenotype is the visible trait and genotype is the gene make-up.
2. Alleles are written as T and t for tall and dwarf.

Answer: (c) If all plants are tall after self-pollination

Explanation:
1. A pure (homozygous) tall plant TT gives only tall plants on self-pollination.
2. A hybrid tall plant Tt gives both tall and dwarf plants.
3. So it is pure if all plants are tall after self-pollination.

Teacher's Note:
1. The two plants look the same, so selfing is needed to tell them apart.
2. Pure plants breed true.

Answer: (a) resemblances and differences between the parents and offsprings.

Explanation:
1. Heredity and variation are studied together.
2. So the subject deals with resemblances and differences between parents and offspring.

Teacher's Note:
1. Resemblances arise from heredity and differences from variation.
2. Genetics covers both.

Answer: (d) gene.

Explanation:
1. A gene is a segment of DNA that carries the information for making a particular protein.
2. The protein produced controls the trait.

Teacher's Note:
1. Chromosomes are made of DNA and carry many genes.
2. A gene is the unit of inheritance.

Answer: (d) All of these

Explanation:
1. Changes in non-reproductive (body) tissues are acquired traits.
2. They do not alter the DNA of the germ cells, so they cannot be passed on and cannot direct evolution.
3. All the given statements are true.

Teacher's Note:
1. Only changes in germ cell DNA are inherited.
2. Acquired traits like muscle gain are lost with the individual.

Answer: (d) Reduction in weight of the organism due to starvation is genetically controlled

Explanation:
1. Loss of weight due to starvation is a change caused by the environment during the lifetime of an individual.
2. It is an acquired trait and is not genetically controlled, so statement (d) is incorrect.

Teacher's Note:
1. Acquired changes do not alter the DNA of germ cells.
2. Parents of low weight can have heavy children because of genes or nutrition.

Answer: (a) Gene

Explanation:
1. Characters are passed from parents to offspring through genes, which are the units of heredity.
2. So the physical basis of heredity is the gene, while its chemical basis is DNA.

Teacher's Note:
1. Genes are segments of DNA on chromosomes.
2. Physical basis = gene, chemical basis = DNA.

Answer: (c) Both (A) & (B)

Explanation:
1. The second generation inherits the traits of the first generation through DNA copying.
2. Small errors in DNA copying and sexual reproduction also add new differences.
3. So it has both inherited traits and newly created differences.

Teacher's Note:
1. Variations accumulate over generations.
2. This is the 'accumulation of variation' in the chapter.

Answer: (c) similar but may have minor differences

Explanation:
1. Bacteria divide asexually, so the offspring are copies of the parent.
2. DNA copying is not perfectly accurate, so the four bacteria are similar but may have minor differences.

Teacher's Note:
1. Asexual reproduction gives very little variation.
2. The small differences come from copying errors.

Answer: (a) yes, as they are responsible for expression of character or trait

Explanation:
1. A gene carries the information for making a protein, which controls a trait.
2. So genes are responsible for the expression of characters or traits.

Teacher's Note:
1. For example, a gene for tallness makes an efficient enzyme that gives a plant-growth hormone.
2. A changed gene gives less hormone and a dwarf plant.

Answer: (b) DNA

Explanation:
1. Genes are made of DNA.
2. The chemical substance that carries hereditary information is DNA.

Teacher's Note:
1. Physical basis is the gene.
2. Chemical basis is DNA.

Answer: (d) Alleles

Explanation:
1. The alternative forms of a gene that decide a pair of contrasting characters are called alleles.

Teacher's Note:
1. Dominant and recessive describe how alleles behave.
2. Tall and dwarf are controlled by alleles T and t.

Answer: (c) Germinal variation

Explanation:
1. Variations in the germ cells are passed to the next generation and are called germinal variations.
2. Somatic or acquired variations occur in body cells and are not inherited.

Teacher's Note:
1. Only changes in the DNA of germ cells are inherited.
2. Learn heritable = germinal.

Answer: (a) Phenotype

Explanation:
1. The visible or observable characteristics make up the phenotype.
2. The genetic make-up is the genotype.

Teacher's Note:
1. A phenotype can be seen, a genotype is written as letters.
2. Example: tall is a phenotype and Tt is a genotype.

Answer: (d) For every molecule of fat there is a gene

Explanation:
1. Genes carry the instructions for making proteins, including enzymes and protein hormones.
2. Fats are not made directly from genes, so there is no gene for every fat molecule.
3. Hence statement (d) is incorrect.

Teacher's Note:
1. A gene codes for a protein.
2. Fat is made by enzymes, which are coded by genes.

Answer: (b) Factors

Explanation:
1. Mendel proposed that traits are controlled by units that he called factors.
2. Later studies showed that these factors are genes.
3. So, according to Mendel, factors were responsible.

Teacher's Note:
1. Mendel knew nothing about genes or chromosomes.
2. The word gene was introduced later.

Answer: (c) TtWW

Explanation:
1. All progeny have violet flowers, so the tall parent must be homozygous violet (WW).
2. Half of the progeny are short (tt), so the tall parent must carry a t allele, i.e. Tt.
3. The tall parent is therefore TtWW.

Teacher's Note:
1. Work trait by trait: height and flower colour separately.
2. A 1 : 1 ratio in a cross with a recessive plant means the other parent is heterozygous.

Answer: (a) Round seeds were more abundant than wrinkled seeds.

Explanation:
1. Round seed shape is dominant over wrinkled.
2. A dominant phenotype is expressed in both RR and Rr plants, so it is more common.
3. Therefore round seeds were more abundant.

Teacher's Note:
1. Dominant traits are generally seen in a larger fraction of a population.
2. In a 3 : 1 ratio the dominant phenotype is three-fourths.

Answer: (b) seven

Explanation:
1. Mendel selected seven pairs of contrasting characters in the garden pea, such as tall/dwarf, round/wrinkled and yellow/green seeds.
2. The number is seven.

Teacher's Note:
1. Seven pairs of contrasting characters means 14 traits in all.
2. This is a frequently asked fact.

Answer: (a) Garden peas

Explanation:
1. Mendel carried out his experiments on the garden pea, Pisum sativum.

Teacher's Note:
1. Garden pea has many easily distinguishable contrasting traits.
2. It is easy to grow and has a short life cycle.

Answer: (d) Laws of inheritance

Explanation:
1. Mendel's laws describe how characters pass from parents to offspring.
2. They are known as the laws of inheritance.

Teacher's Note:
1. Mendel's laws are dominance, segregation and independent assortment.
2. The other options belong to different topics.

Answer: (b) Monohybrid cross

Explanation:
1. The law of segregation (purity of gametes) was formulated from experiments in which only one pair of contrasting characters was studied.
2. Such experiments are monohybrid crosses.

Teacher's Note:
1. Independent assortment was based on dihybrid crosses.
2. Segregation was based on monohybrid crosses.

Answer: (a) Both A and R are true, and R is the correct explanation of A.

Explanation:
1. Skills such as dance and music are learned during life, so they are acquired traits and A is true.
2. Acquired traits develop in an individual's lifetime and are not passed on, so R is true and it explains A.

Teacher's Note:
1. Acquired traits do not change the DNA of germ cells.
2. Examples are learned skills, loss of weight or loss of a body part.

Answer: (c) A is true, but R is false.

Explanation:
1. Eye colour and height are controlled by genes, so they are inherited traits and A is true.
2. Inherited traits are exactly the traits transferred from parents to young ones, so R is false.

Teacher's Note:
1. Inherited traits are passed through genes.
2. Acquired traits are the ones that are not passed on.

Answer: (d) A is false, but R is true.

Explanation:
1. Variations do not always help; some are harmful or neutral, so A is false.
2. Errors in DNA copying do produce variations, so R is true.

Teacher's Note:
1. A variation helps only if it suits the environment.
2. DNA copying errors and sexual reproduction are the sources of variation.

Answer: (c) A is true, but R is false.

Explanation:
1. Traits that come from parents through genes are inherited traits, so A is true.
2. Traits developed in the parents during their lifetime are acquired traits and are not passed on, so R is false.

Teacher's Note:
1. Inherited traits are controlled by genes.
2. Acquired traits change only body cells.

Answer: (a) Both A and R are true, and R is the correct explanation of A.

Explanation:
1. Tall (T) and dwarf (t) are alternative forms (alleles) of the same gene for height, so A is true.
2. R states this fact, so it explains A.

Teacher's Note:
1. Alleles occupy the same position on homologous chromosomes.
2. Different genes control different characters.

Answer: (a) Both A and R are true, and R is the correct explanation of A.

Explanation:
1. Garden pea has clearly contrasting characters, a short life cycle and easy self- and cross-pollination.
2. These features made it ideal, which explains Mendel's success.

Teacher's Note:
1. Mendel also counted large numbers of progeny.
2. A good choice of experimental material is important in any experiment.