Wednesday 16 December 2020

Chapter 9 Heredity and Evolution


Chapter 9 Heredity and Evolution

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 the tall parent can be depicted as:
(a) TTWW
(b) TTww
(c) TtWW
(d) TtWw

(c) TtWW

Question 2.
An example of homologous organs is :
(a) our arm and a dog’s fore-leg
(b) our teeth and an elephant’s tusks
(c) potato and runners of grass
(d) all of the above

(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

(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 ?

This information is not complete. On the basis of this, it cannot be decided light colour trait is dominant or recessive. So it cannot be said until one does not know the nature of this trait in the parents.

Question 5.
How are the areas of study-evolution and classification interlinked ?
‘Two areas of study namely ‘evolution’ and ‘classification’ are interlinked”. Justify this statement. [AICBSE 2016]

Classification of organisms is based on relative similarities and differences among organisms. Resemblances in organisms are because they have arisen from a common ancestor and differences in them are due to adaptations to different types of environment. Since the organisms can be graded in order of increasing complexity it indicates at the concept of evolution.

Question 6.
Explain the terms analogous and homologous organs with examples. [CBSE 2011,2013, 2014]

Analogous organs : Those organs which have different basic structure (or different basic design) but have similar appearance and perform similar functions are called analogous organs.
For example, The wings of an insect and a bird are analogous organs.

Homologous organs :  Those organs which have the same basic structure (or same basic design) but different functions are called homologous organs.
For example, The wing of a bat, flipper of a seal, front leg of a horse and arm of a man are homologous organs.

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

Suppose a black homozygous male is mated with a white homozygous female. If the progeny has all black dogs then the dominant coat colour is black.

Question 8.
Explain the importance of fossils in deciding evolutionary relationships.

Fossils play important role in providing evolutionary evidences because by knowning the age of fossils we can know about the evolution process of an organism.
For example, a fossil bird called archaeopteryx that looked like a bird had many other features of reptiles. It had feathered wings like those of birds, but teeth and tail like those of reptiles. Archaeopteryx is, therefore, a connecting link between the reptiles and birds, and hence suggests that the birds have evolved from the reptiles.

Question 9.
What evidence do we have for the origin of life from inanimate matter ? [CBSE 2011, 2014]

A British scientist J.B.S. Haldane at first in 1929 suggested that life is originated from inanimate matter. According to him life must have developed from the simple inorganic molecules which were present at that time. Later, Miller and Urey in 1953 presented its evidences. They assembled an apparatus to create an early earth atmosphere which was supposed to consist of gases like methane, ammonia and hydrogen sulphide, etc. over water. This was maintained at a temperature just below 100°C and electric sparks were then passed through the mixture of gases to stimulate lightning for about one week. At the end of one week, it was found that about 15 per cent of carbon (from methane) had been converted into simple compounds and amino acids which make up protein molecules formed in living organisms. This experiment provides the evidence that the life originated from inanimate matter (or lifeless matter) like inorganic molecules.

Question 10.
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 ? [CBSE 2011,2014]

During sexual reproduction there is ‘crossing over’ of chromosomes, that gives rise to variations. These variations are inherited and increase the chances of survival of an organism.

1.     In sexual reproduction variations may occur due to errors in DNA copying.

2.     There may be variations due to interchange of homologous chromosomes during crossing over of male and female.

3.     In sexual reproduction, it is not predetermined that which gamete would fuse with another gamete. It depends only on chance. It is also a reason of variation.
These variations enable the organisms to adapt themselves to the changing conditions and also help to give rise to new species.

Question 11.
How is the equal genetic contribution of male and female parents ensured in the progeny ? [CBSE 2011, 2013]

Genetic material in most organisms is present in pairs of chromosomes. Gametes in the sexually reproducing organisms are formed by the process of meiosis during which half of the genetic material goes into each gamete. When the gametes from male and female parents fuse with each other during sexual reproduction, the normal complement is restored. Half of the genetic material comes from the female and half from the male.

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?

Yes, variations that confer an advantage to an individual organism are inherited. The organism can survive longer in an environment and maintain its existence in the population.