CBSE Class 10 Science Heredity and Evolution Assignment Set C

Question. State whether the following statement is true or false : Human beings have evolved from chimpanzees.
Answer : False

Question. Write the names of at least three inorganic molecules which helped in the origin of life on the earth.
Answer : Methane, ammonia and hydrogen sulphide are three inorganic molecules, which helped in the origin of life on the earth.

Question. Name the famous book written by Charles Robert Darwin.
Answer : The Origin of Species

Question. The forelimbs of a frog, a bird and a man show the same basic design (or basic structure) of bones. What name is given to such organs ?
Answer : Homologous organs

Question. Name two organisms which are now extinct and studied from their fossils.
Answer : Trilobites (marine arthropods) and dinosaurs

Question. Out of the wing of a bird, wing of an insect and the wing of a bat :
(a) which two are homologous organs ?
(b) which two are analogous organs ? 
Answer : (a) Wings of bird and wings of bat (b) Wings of birds and wings of insect

Question. State one characteristic which shows that the birds are very closely related to dinosaurs.
Answer : The presence of feathers on birds

Question. Name an animal having rudimentary eyes.
Answer : Planaria has rudimentary eyes.

Question. Name the ancestor of the following : Broccoli, Kohlrabi, Kale
Answer : Wild cabbage

Question. Where did life originate on the earth ?
Answer : the ocean

Question. Why are human beings who look so different from each other in terms of size, colour and looks said to belong to the same species ?
Answer : Human beings apart from these variations are said to belong to the same species because humans had descended from a common ancestor and also they have a lot of similarities in their DNA patterns. The variations present in size, colour, and looks are due to the expression of genetic traits at different levels.

Question. Name five varieties of vegetables which have been produced from ‘wild cabbage’ by the process of artificial selection.
Answer : Broccoli, cabbage, cauliflower, kohlrabi and kale are five varieties of vegetables, which have been produced from 'wild cabbage' by the process of artificial selection.

Question. Choose the one term from the following which includes the other three : broccoli, wild cabbage, cauliflower, cabbage
Answer : Wild cabbage

Question. What name is given to the sequence of gradual changes over millions of years in which new species are produced ?
Answer : Evolution

Question. Name the scientist who gave the theory of evolution.
Answer : Charles Darwin

Question. (a) What is meant by ‘heredity’ ? What are the units of heredity.
(b) State Mendel’s first law of inheritance.
Answer : (a) The transmission of characters from parents to the offspring's is called heredity. The units of heredity are genes. (b) According to Mendel's first law of inheritance: The characteristics (or traits) of an organism are determined by internal 'factors' which occur in pairs.

Question. (a) Why did Mendel choose pea plants for conducting his experiments on inheritance ?
(b) State Mendel’s second law of inheritance.
Answer : (a) Mendel selected garden pea plant for his experiments because of the following characteristics:
(i) The flowers of this plant are bisexual.
(ii) They are self-pollinating, and thus, self and cross pollination can easily be performed.
(iii) The different physical characteristics were easy to recognise and study.
(iv) They have a shorter life span and are the plants are easier to maintain.
(b) According to Mendel's law of independent assortment, during the inheritance of two or more characters, the assortment of individual traits takes place independently during gamete formation. Thus each allele of a pair segregates independently and each gamete formed contains one allele of that trait. This law is inapplicable for linked genes. 

Question. (a) What do you understand by the term ‘variation’ ?
(b) Name two human traits which show variation.
(c) How does the creation of variation in a species ensure its survival ?
Answer : (a) The differences in the characters (or traits) among the individuals of a species is called variation.
(b) Human height and skin colour are two traits which show variation.
(c) The great advantage of variation to a species is that it increases their chances of survival in a changing environment.

Question. (a) What are genes ? Where are they located in our body ?
(b) What is meant by dominant genes and recessive genes ? Give one example of each.
(c) Explain how, characteristics (or traits) are inherited through genes.
Answer : (a) Genes are the units of heredity which transfer characteristic from parents to their offspring’s during reproduction. Genes are located on the chromosomes inside the nucleus of our cells in the body. .
(b) The gene which decides the appearance of an organism even in the presence of an alternative gene is known as dominant gene. The gene which can decide the appearance of an organism only in the presence of another identical gene is called a recessive gene. The dominant gene is represented by a capital letter and the corresponding recessive gene is represented by the corresponding small letter. For example, in pea plants, the dominant gene for tallness is T and the recessive gene for dwarfness is t.
(c) There are a pair of genes for each characteristic of an organism, while one is dominant gene and the other is recessive gene. Each parent passes only one of the two genes of the pair for each characteristic to its progeny through gametes. Thus, the male gamete and the female gamete carry one gene for each characteristic from the gene pairs of the parents. When a male gamete fuses with a female gamete during fertilisation they make a new cell called zygote which grows and develops to form a new organism having characteristics from both the parents which it has inherited through genes.

Question. (a) How do Mendel’s experiments show that traits may be dominant or recessive ?
(b) How do Mendel’s experiments show that traits are inherited independently ?
Answer : (a)Mendel selected true breeding tall (TT) and dwarf (tt) pea plants. When a tall pea plant is crossed with a short (dwarf) pea plant, all the F1 hybrids are tall. (i.e., in this case, the gene causing tallness is dominant while the gene causing dwarfness is recessive.).The trait expressing itself in the hybrid is the dominant one. Mendel’s first law of inheritance states that when a pair of contrasting factors is brought in a hybrid, one factor inhibits the appearance of the other. The one which inhibits is the dominant one and which is inhibited is recessive.
(b)Mendel performed an experiments in which he took a tall plant with round seeds and a short plant with wrinkled-seeds. In F1, They were all tall and had round seeds. Tallness and round seeds were thus dominant traits. When, he used these F1 progeny to generate F2 progeny by self-pollination, he found that some F2 progeny were tall plants with round seeds, and some were short plants with wrinkled seeds. At the same time there tall plants, but had wrinkled seeds, while others were short, but had round seeds. Thus, Mendel’s experiments show that the tall/short trait and the round seed/wrinkled seed trait are independently inherited.

Question. Pure-bred pea plants A are crossed with pure-bred pea plants B. It is found that the plants which look like A do not appear in F1 generation but re-emerge in F2 generation. Which of the plants A and B are : (i) tall, and (ii) dwarf ? Give reason for your answer.
Answer : (i) B (ii) A ; Dwarf pea plants do not appear in F1 generation

Question. Pure-bred tall pea plants are first crossed with pure-bred dwarf pea plants. The pea plants obtained in F1 generation are then cross-bred to produce F2 generation of pea plants.
(a) What do the plants of F1 generation look like ?
(b) What is the ratio of tall plants to dwarf plants in F2 generation ?
(c) Which type of plants were missing in F1 generation but reappeared in F2 generation ?
Answer : (a) All tall plants (b) 3 : 1 (c) Dwarf plants

Question. A plant has two varieties, one with red petals and the other with white petals. When these two varieties are cross-pollinated, all the offsprings have red petals ?
(a) Which gene is dominant ?
(b) Choose suitable letters to represent the two genes.
Answer : (a) Red colour (b) Rr

Question. A red-haired woman marries a brown-haired man, and all the children are brown haired. Explain this genetically.
Answer : The brown hair colour genes are dominant to the red hair colour genes ; The genotype of brown hair can be represented as BB and that of red hair as bb

Question. A black mouse mates with a brown mouse, and all the offsprings are black.
(a) Why are no brown offsprings produced ?
(b) If two of the black offpsrings mate with each other what kind of offspring would you expect and in what proportions ? Give reason for your answer.
Answer : (a) Because black colour genes are dominant over brown colour genes (b) Three black mice and one brown mouse will be obtained in F2 generation ; It is a monohybrid cross

Question. (a) E is the gene for brown eye colour and and e is the gene for blue eye colour. Which gene is (i) recessive, and (ii) dominant ?
(b) Both father and mother have the genes Ee in their cells. What colour are their eyes ?
(c) Which combination of genes in the zygote will produce children with blue eyes ?
(d) Which combinations of genes in the zygote will produce children with brown eyes ?
Answer : (a) (i) e (blue colour) (ii) E (brown colour) (b) Brown eyes (c) ee (d) EE and Ee

Question. What are the possible blood groups likely to be inherited by children born to a group A mother and a group B father ? Explain your reasoning.
Answer : Possible genotypes are IA IB, IA IO, IB IO and IO IO. So, the possible phenotypes or blood groups are : AB, A, B and O

Question. A couple with a newborn baby is troubled that the child does not resemble either of them. Suspecting that a mixup occurred at the hospital, they check the blood type of the infant. It is type O. Because the father is type A and the mother type B, they conclude that a mixup has definitely occurred. Are they correct ? Give reason for your answer.
Answer : No, the parents are not correct. The baby born to father having blood groups A and mother having blood group B can have any one of the four possible blood groups : A, B , AB and O.

Question. A man with blood group A marries a woman with blood group O and their daughter has blood group O. Is this information enough to tell you which of the traits—blood group A or O — is dominant ? Why or why not ?
Answer : No (Case I : If father’s blood group A is dominant trait, his genotypes will be IAIA and IAIO; and mother’s blood group O being recessive trait, her genotype will be IOIO.
So, daughter can receive one recessive allele IO from father and another recessive allele IO from mother to have genotype IOIO and hence blood group O. Case II : If father’s blood group A is recessive trait, his genotype will be IAIA; and mother’s blood group O being dominant trait, her genotypes will be IOIO and IOIA. In this case, daughter can receive a dominant allele IO from mother and a recessive allele IA from father to have genotype IOIA and hence blood group O).

Question. A Mendelian experiment consisted of breeding tall pea plants bearing violet flowers with short pea plants bearing white flowers. The progeny all bore violet flowers, but almost half of them were short. This suggested that the genetic make up (or genotype ) of the tall parent can be depicted as :
(a) TTWW (b) TTww (c) TtWW (d) TtWw
Give reason for your choice.
Answer : (c) TtWW (Hint. T is the gene form for tallness, t for dwarfness, W for violet colour and w for white colour. T and W are dominant genes whereas t and w are recessive genes)

Question. A person first crossed pure-bred pea plants having round-yellow seeds with pure-bred pea plants having wrinkled-green seeds and found that only A-B type of seeds were produced in the F1 generation. When F1 generation pea plants having A-B type of seeds were cross-bred by self-pollination, then in addition to the original round-yellow and wrinkled-green seeds, two new varieties A-D and C-B type of seeds were also obtained.
(a) What are A-B type of seeds ?
(b) State whether A and B are dominant traits or recessive traits.
(c) What are A-D type of seeds ?
(d) What are C-B type of seeds ?
(e) Out of A-B and A-D types of seeds, which one will be produced in (i) minimum numbers, and
(ii) maximum numbers, in the F2 generation ?
Answer : (a) Round yellow (b) A (round) and B (yellow) are dominant traits (c) Round-green (d) Wrinkled-yellow (e) (i) A–D (ii) A–B

Question. The person A has only B chromosomes in all its gametes. On the other hand, another person C has chromosome D in half of gametes and chromosome E in the other half of gametes. When chromosomes B and D combine during fertilisation, a female zygote results. On the other hand, combination of B and E chromosomes produces a male zygote.
(a) What are chromosomes (i) B (ii) D, and (iii) E ?
(b) Out of B, D and E, which two chromosomes are of the same type ?
(c) Which chromosome is smaller in size ?
(d) What is the general name of chromosomes such as B and E ?
(e) Out of the two persons A and C, which one is (i) male, and (ii) female ?
Answer : (a) (i) X chromosomes (ii) X chromosome (iii) Y chromosome (b) B and D (both are X chromosomes) (c) E (d) Sex chromosomes (e) (i) C (ii) A

Question. Mendel first crossed pure-bred pea plants having round-yellow seeds with pure-bred pea plants having wrinkled-green seeds and found that only round-yellow seeds were produced in the F1 generation. When F1 generation pea plants having round-yellow seeds were cross-bred by self pollination, then peas having roundyellow seeds, round green seeds, wrinkled-yellow seeds and wrinkled-green seeds were produced. Mendel collected a total of 2160 seeds.
(a) What will be the number of (i) round green seeds (ii) wrinkled green seeds (iii) round yellow seeds, and (iv) wrinkled-yellow seeds ?
(b) Which ‘ratio’ as established by Mendel have you made use of in answering the part (a) above ?
Answer : (a) (i) 405 (ii) 135 (iii) 1215 (iv) 405 (b) Dihybrid ratio

Question. Pure-bred round-yellow pea seeds have genotype RRYY and the pure-bred wrinkled-green pea seeds have genotype rryy. Keeping this in mind, write the phenotypes of the following genotypes of hybrid pea seeds :
(a) Rryy (b) rrYy (c) rrYY (d) RrYy (e) RRyy
Answer : (a) Round-green (b) Wrinkled-yellow (c) Wrinkled-yellow (d) Round-yellow (e) Round-green