Heredity and Evolution

NCERT Exercise Solution

Question:1 .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 suggests that the genetic make- up of tall parent can be depicted as:

(a) TTWW

(b) TTww

(c) TtWw

(d) TTWw

Answer: ( c)TtWW

Question: 2. An example of homologous organ is

(a) our arm and a dog?s foreleg

(b) our teeth and an elephant?s tusks

( c) Potato and runner of grass

(d) all of the above

Answer: (d) all of the above

Question: 3 .In evolutionary terms, we have more in common with

(a) a Chinese school boy

(b) a chimpanzee

(c ) a spider

(d) a bacterium

Answer: (a )a Chinese school boy

Question: 4. 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: Light- coloured eye is a dominant trait because children born from the parents having light-Coloured eyes also had light- coloured eyes.

Question: 5. How are the areas of study ? evolution and classification- interlinked?

Answer: The two species having many common characteristics are considered to be closely related and have originated from common ancestor. The modern classification is bassed on the phylogenetic resemblances between the species. Systematic is the branch of taxonomy which deals with the classification of living beings on the basis of evolution.

Question:6 . Explain the terms analogous and homologous organs with example.

Answer: The organs having similar functions but different structures and origin are said to be analogous organs, like the wings of a bird, an insect and a bat.

The organs having similar structure and origin but different functions are said to be homologous organs, like the hand of man, wing of a bird and forelimb of a house.

Question: 7 . Outline a project which aims to find the dominant coat colour in dogs.

Answer: (a) Select two varieties of dogs one with white coat colour, the other with black coat colour.

(b) Crossbreed them taking male dog from one variety and birth (female dog) from the other variety.

( c) Observe the colour of offspring of F¹ generation.

(d) Now, bring about the breeding among the organisms of F¹ generation.

(e) Observe the coat colour of organisms (pups) of F² generation and note their coat colour variations.

(f) Draw conclusions on the basis of your study.

One of the probable inheritance pattern may be as under.

Black coat colour: white coat colour, Phenotypic ratio=3:1

Question:8. Explain the importance of fossils in deciding evolutionary relationship.

Answer: fossil play an important role is deciding evolutionary relationships as follows:

(a) The fossils present in the bottom rocks are simple while the most recent fossils found in the upper strata are highly complex. This geographical succession completely agrees with the concept of evolution.

(b)Some fossils provide a connecting link between two groups, e.g., study of fossils o bird Archeopteryx indicates that birds have evolved from reptile- like ancestors.

(c)Fossil records of certain mammals (horse, elephant, camel, man, etc.)if arranged era-wise would present a complete series indicating how their evolution occurred.

Fossils of the bodies of dinosaurs with feathers have been found in the rocks which were not used for flying by dinosaurs but they were meant for giving warmth to the body .They must have evolved into wings later meant for flying as seen in birds. This shows a close relationship between birds and reptiles.

Question:9. What evidence do we have for the origin of life from inanimate matter?

Answer: Experimental evidence provided by miler and Urey proves the origin of life from inanimate matter. They designed an apparatus with glass tube and flasks. In the apparatus, they circulated a mixture of methane, ammonia, hydrogen in the ratio of 2:2:1 and water vapour. These gases were believed to be present in the ancient atmosphere. Energy was provided by electric spark in the gas flask. The mixture was maintained at a temperature just below 100₀ C. The experiment was kept working continuously for 18 days and then the condensed material was chemically analysed. A large number of organic substances including amino acids (glycine, ananine and aspartic acid) urea, lactic acid simple sugar, purine, pyrimidine, etc. were found in the condensed mixture which proved the abiotic synthesis of organic molecules in the process of origin of life.

Question: 10. Explain how sexual reproduction gives rise to more viable variation than asexual reproduction. How does this affect the evolution of those organisms that reproduce sexually?

Answer: During sexual reproduction at the time of gamete formation, meiotic cell division takes place. During meiosis crossing over between fragments of homologous chromosomes occurs which brings about new gene combinations to be transferred to new generation. Crossing over is the fundamental cause of origin of variation in sexually reproducing organisms. Asexual reproduction does not involve meiosis and crossing over because of one parent lineage. Hence, only minute variations may occur in them due to mutation.

The variations caused by crossing over in sexually reproducing organisms are subjected to the selection process. Natural selection selects those variations which have more adaptive value and guide them towards evolution of new form. In this way, sexual reproduction gives rise to more viable variations for evolution.

Question:11 . How is the equal genetic contribution of male and female parents ensured in the progeny?

Answer: A zygote is formed by the fusion of sperm and ova. During the formation of gametes as a result of redctional division (meiosis), sperm and eggs receive only single genome of a parent i.e., half of the genetic material of parent cell. When fertilization occurs, one genome each from sperm and egg reaches the zygote, thus the zygote becomes diploid (2n). In this way, both male and female parents contribute exactly equal amount of genetic material to the offspring.

Question: 12. 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: It is not always true. The variations that confer an advantage to an individual organism are definitely of more survival value because natural selection prefers these variations. But there are several other variations which, though do not provide advantage to the organism in the present condition, survive and are inherited to the next generations Such non advantgeous variations may become advantageous in future when the condition of environment changes.