CBSE Class 10 Biology Heredity And Evolution Worksheet Set D

Objective Questions

Case Study Question

In some animals, the temperature at which fertilised eggs are kept determines whether the animal developing in the egg will be male or female. In other animals, such as snails, individuals can change sex, that is sex is not genetically determined. In human beings, sex of individuals is largely genetically determined. All chromosomes in human beings are not paired. We have 22 pairs and one pair of sex chromosomes which is odd and not always a perfect pair.

Question : Which pair of chromosomes are present in Male
(a) XX
(b) YY
(c) XY
(d) XXY
Answer : C

Question : How many pairs of chromosomes are called autosomes?
(a) 23
(b) 22
(c) 21
(d) 20
Answer : B

Question : Who is responsible for birth of male child?
(a) Father
(b) Mother
(c) Father only in first pregnancy.
(d) Mother only in first pregnancy
Answer : A

Question : Which pair of chromosomes are present in female?
(a) XX
(b) YY
(c) XY
(d) XXY
Answer : A

Question : Which of the following statement is true?
(a) Men have short sized X chromosome
(b) Men have one long sized Y chromosome
(c) Men have normal sized Y chromosome
(d) Men have one short sized Y chromosome
Answer : D

Very Short Answer Questions

Question : Define speciation.
Answer : Speciation means origin of new species from the existing one.

Question : How are characters or traits controlled?
Answer : Characters or traits of an organism are controlled by the genes /DNA.

Question : In a beetle population, the number of green beetles is more than blue and red beetles. Give a reason behind this situation.
Answer :  Variation/Natural selection.

Question : What is genetic drift?
Answer :  The change in the frequency of certain genes in a population over generations.

Question : What is heredity?
Answer : Transmission of characters and traits from one generation to the next.

Question : How many pairs of chromosomes are present in human beings?
Answer :  23 pairs.

Question : Name the term used for the traits that are exhibited externally.
Answer : Phenotype.

Question : An organism which is a worm, has very simple ‘eyes’, that are really eye spots which detect light. Name that organism.
Answer :  Planaria.

Question : Why is the progeny always tall when a tall pea plant is crossed with a short pea plant?
Answer : The trait which represents the tallness in a pea plant is dominant over the another trait, shortness (dwarf).

Question : Human have evolved from chimpanzee. Is it true? 
Answer :  No, the two species have evolved in separate ways from a common ancestor.

Question : Why is it that asexual reproduction produces exact copies but sometimes minor variations are also seen in next progeny?
Answer :  Since no biochemical reaction is reliable, therefore, in copying of DNA, it may cause slight difference which causes these variations.

Question : How can the chromosomes be identified?
Answer :  In human beings, the individual chromosomes are identified by their lengths, position of centromere and banding pattern on staining.

Question : No two individuals are absolutely alike in a population. Why?
Answer :  All individuals have different kind of DNA. So all individuals are not alike to each other.

Question : What is a gene?
Answer :  It is a functional piece of DNA that is responsible for expression of a trait in the organisms.

Question : What indication do we get by reappearance of dwarf plant in F₂ generation?
Answer :  After obtaining progeny in F₂ generation in a dihybrid cross, Mendel concluded that when two pairs of traits are combined in a hybrid, one pair of character segregates independently of the other pair of character.

Question : Mendel observed a contrasting trait in relation to position of flowers. Mention the trait.
Answer : Axial flower position (dominant), terminal flower position (recessive).

Question : Write the sex of the baby that inherits Y-chromosomes from the father.
Answer :   Male.

Question : What is the phenotypic ratio of a dihybrid cross in F₂ generation?
Answer :  9 : 3 : 3 : 1.

Question : What is the effect of DNA copying which is not perfectly accurate on the reproduction process?
Answer :  It will result in less variations which may further lead to less adaptation to changing environment, thus, giving less chances of survival.

Question : What are the basic events in evolution?
Answer :  The changes in DNA during reproduction are the basic events in evolution.

Question : All the variations in a species do not have equal chances of survival. Why?
Answer : Some variations are caused by environmental changes and they do not bring out any change in DNA.Therefore, all the variations do not have equal chances of survival.

Question : What are fossils?
Answer :  Preserved traces of living organisms.

Question : How can the chromosomes be identified?
Answer : In human beings, the individual chromosomes are identified by their lengths, position of centromere and banding pattern on staining.

Question : What are analogous organs?
Answer :  The organs which have similar functions but different structures are called analogous organs.

Question : How is the age of fossil determined?
Answer :  The age of fossil fuels is determined through carbondating or time dating method.

Question :  A Mendelian experiment consisted of breeding pea plants bearing violet flowers with pea plants bearing white flowers. What will be the result in Fj progeny?
Answer :  All will bear violet flowers.

Question : What is evolution?
Answer : Gradual unfolding of organisms from pre-existing organisms through change is called evolution

Question : Name the plant on which Mendel performed his experiments.
Answer :  Garden pea (Pisum sativum).

Question : Give an example where sex determination is regulated by environmental factors.
Answer : In snail, sex is determined by environmental factors (temperature).

Question : When does the process of gene flow take place?
Answer : Gene flow or gene migration takes place in between the populations that are partly but not completely separated.

Question : What is speciation?
Answer : Speciation is the process of formation of a new species from the already existing species by accumulation of variations, natural selection, gene flow, genetic drift, etc.

Question : What is artificial selection?
Answer : It is the process of modification of a species by selective breeding. Animals and plants with desirable characters are selected and propagated. Artificial selection by farmers has resulted in the formation of cauliflowers, cabbage, broccoli and kohlrabi from the wild cabbage.

Question : What is a gene?
Answer : Gene is the unit of inheritance. It is a part of the chromosome which controls the appearance of a set of hereditary characteristics.

Question : Name two human traits that show variations.
Answer : Colours of eyes and shape of external ears.

Question : What is evolution?
Answer : Evolution is the sequence of gradual changes which take place in living organisms over millions of years to give rise to new species.

Question : What are fossils?
Answer : Fossils are preserved traces or remains of living organisms of geological past.

Question : Who is known as the ‘‘father of Genetics’’?
Answer : G.J. Mendel is called the ‘‘father of Genetics’’.

Question : Name the scientist who put forth the theory of natural selection.
Answer : Charles Darwin.

Short Answer Questions

Question : The chromosome number of the sexually reproducing parents and their
offspring is same."" Justify the statement.
Answer : In sexually reproducing organisms, male and female gametes /reproductive cells with only half the number of chromosomes (as in the parent cell) are produced. during fertilization, when male and female gametes fuse to give to a zygote, original number of chromosomes are restored.

Question : Genes controls traits ' . Explain this statement with an example.
Answer :  Genes controls traits by synthesizing the specific enzyme. Plant height depends on the amount of a particular plant hormone. The amount of plant hormone made will depends on enzyme. If enzyme work efficiently the plant will be tall. if the gene for that enzyme has an alteration that makes enzyme less efficient, the amount of hormone will be less and plant will be short.

Question : What is DNA copying? State its importance.
Answer : DNA copying is the process of producing two identical replicas from one original DNA molecule during cell division.
DNA is necessary to make all the RNA and proteins needed for cells to carry out necessary reactions and cellular processes in order to survive.

Question : Differentiate between phenotype and genotype?
Answer : Genotype – It is the complete heritable genetic identity of an organism. It is the set of alleles that are carried by the organism. It also includes non- expressed alleles.
Phenotype – It is the description of the actual physical characteristics of an organism or the expressed form of the genotype.

Question : A study found that children with light-coloured eyes are likely to have parents with light-coloured eyes. On this basis, can we say anything about whether the light eye colour
trait is dominant or recessive? Why or why not?
Answer :  No, we cannot say that the traits is recessive or dominant unless we know the nature of the two variants of a trait.

Question : Explain the terms analogous and homologous organs with examples.
Answer : Analogous organs—Organs with different structure and same function e.g., wings of bird, insects.
Homologous organs—Organs which have same structure but different functions are called homologous organ e.g., forearm of lizard, bird and human.

Question : Explain the importance of fossils in deciding evolutionary relationships.
Answer :  Fossils help us to know the following:
(a) Fossils help to trace the racial history of organisms.
(b) They help to measure the geological time.
(c) Older fossils lie at the depth and young fossils are at the upper surface of the  earth. Complex organisms are present at top and simple organisms are present at the bottom.
(d) Fossil like—Archaeopteryx-show the link between two different types of species.

Question : Explain how sexual reproduction gives rise to more viable variations than asexual reproduction. How does this affect the evolution of those organisms that reproduce sexually?
Answer : Variations are seen more in sexual reproduction than asexual reproduction because variations occur due to change in DNA coding and due to sexual reproduction in which two genes from two different sexes i.e., male and female genes crossing over takes place and hence cause the variation.

Question : Only variations that confer an advantage to an individual organism will survive in a population. Do you agree with this statement? Why or why not?
Answer : No, depending on the nature of variations different individuals have different kinds of advantages. However, when a drastic change occurs in environment only those organism in the population will survive which have an advantageous variation in that population to survive in changed environment.

Question : Give the respective scientific terms used for studying:
a. the mechanism by which variations are created and inherited, and
b. the development of new type of organisms from the existing ones.
Answer : 
a. Heredity
b. Species

Question : What are fossils? What is their significance in the study of evolution?
Answer :  Fossils are impressions of the body/ body parts or the remains of organisms living in the past, which got preserved in sediments of earth.
a. Study of fossils helps in working out evolutionary relationships.
b. Fossils provide one of the most acceptable evidences in support of evolution, because we can study the evolutionary past of individuals in the form of their fossils.
c. Age of fossils can also be found by time dating using isotopes of carbon! carbon dating.
d. By studying fossils occurring in different strata of rocks, geologists are able to reconstruct the time course of evolutionary events.

Question : When a tall and dwarf pea plant were crossed, Fx showed only tall plants but in F2 generation, some plants were dwarf. What does it mean?
Answer : It means reappearance of the dwarf character, a recessive trait in B’2 generation shows that the dwarf trait/ character was present in individuals of F* but it did not express (due to the present of tallness, a dominant trait / character)

Question :  (a) On what rules inheritance is based?

(b) Is each trait influenced by both paternal and maternal DNA?
Answer : 
a. The rules of inheritance is based on the fact that the traits in the progeny are carried out by DNA’s of both the parents (mother and father). These rules are known s ‘Mendel’s Laws of Inheritance’.
The rules are:
(i) Law of dominance,
(ii) Law of segregation, and
(iii) Law of independent assortment.
b. Yes, it is true that each trait is influenced by both paternal and maternal DNA.

Answer : Determination of the sex of child. Sex chromosomes determine sex in human beings.

In males, there are 44 + XY chromosomes, whereas, in female there are 44 + XX chromosomes. Here X and Y chromosomes determine sex in human beings.

Two types of gametes are formed in male, one type is having 50%, X-chromosome, whereas, other type is having Y-chromosome. In female, gametes are of one type and contain X-chromosome.

The females are homogametic. If male gamete having Y-chromosome (endosperm) undergoes fusion with female gamete having X-chromosome the zygote will have X Y chromosomes and this gives rise to male child.

If male gamete having X-chromosome undergoes fusion with female gamete having Xchromosome, the zygote will be having XX-chromosome and this gives rise to female child.

More Question

Q1)Who is known as father of genetics?

Q2)Write the scientific name of the plant on which Mendel carried out his experiment.

Q3)How many chromosomes are present inhuman beings?

Q4)What is the genetic material?what is its importance?

Q5)What are recessive genes?

Q6)What are dominant genes?

Q7)Name the cells which possess half the number of chromosomes in human beings? (hint-germ or reproductive cells)

Q8)State the advantages of sexual reproduction?

Q9)Name any two contrasting characters noticed by Mendel in the garden pea plants.

Q10)State the ratio of plants produced in the monohybrid cross in the F1 and F2 generation?

Q11)Where are genes located? What is the chemicals nature of genes?

Q12)How is the sex of a newborn child determined inhumans?

Q13)Why did Mendel choose pea plant for his experiment?

14) Give reasons why acquired characters are not inherited.

Q15) What are the functions played by DNA?

Q16) What observations did Mendel make during his experiments?