NCERT Solutions for Class 10 Science
Chapter 9- “Heredity and Evolution”
by "Farrukh Asif"
Answer The Following Question.
1. If a trait A exists in 10% of a population of an asexually reproducing species and a trait B exists in 60% of the same population, which trait is likely to have arisen earlier?
Answer :
In asexual reproduction, the reproducing cells produce a copy of their DNA through some chemical reactions. However, this copying of DNA is not accurate and therefore, the newly formed DNA has some variations.
It can be easily observed in the above figure that in asexual reproduction, very few variations are allowed. Therefore, if a trait is present in only 10% of the population, it is more likely that the trait has arisen recently. Hence, it can be concluded that trait B that exists in 60% of the same population has arisen earlier than trait A.
2. How does the creation of variations in a species promote survival?
Answer :
Depending on the nature
of variations different individuals would have difference kinds of advantage to
adjust in particular habitat. Variation help the individual to have different
traits that may develop the organisms more tolerable.
Answer :
In Monohybrid cross of
Mendel between tall and dwarf pea plant, all progeny in F1 generation are tall
and in F2 generation, 75% of pea plants are tall but 25% are dwarf. This shows
that traits are dominant or recessive.
4. How do Mendel’s
experiments show that traits are inherited independently?
Answer :
When a pea plant having
round green seeds is crossed with a pea plant having wrinkled yellow seeds in
F1 generation all the plants have round yellow seeds. But in F2 generation two
new traits that is round yellow and wrinkled green appear. This shows that
traits are inherited independently.
Answer :
No, the information is
not enough because the blood group is determined by a pair of gene. One
inherited from mother and other from father. In this case, the child inherited
gene for O blood group from mother as well as father.
6. How is the sex of the child determined in human beings?
Answer :
A child which inherits X
chromosome from her father will be a girl and one who inherits Y chromosome
from him will be a boy.
7. What are the different ways in which individuals with a particular
trait may increase in a population?
Answer :
The different ways in
which individual with a particular trait may increase are:
(a) Natural selection-
Certain variations give survival advantage to individuals in a population in a
changed situation resulting in increase of their population.
(b) Genetic drift-
Accidents in small population even if they give no survival advantage also lead
to increase to certain individual in population.
8. Why are traits acquired during the life-time of an individual not
inherited?
Answer :
Any change in
nor-reproductive tissues cannot be passed on to the DNA of the germ cells. Therefore,
the traits acquired during life-time on an individual are not inherited.
9. Why are the small
numbers of surviving tigers a cause of worry from the point of view of
genetics?
Answer :
It will affect the
frequency of selection which is essential for survival. For effective
selection, the population must consist of an infinitely large number of
individual in population.
10. What factors could lead to the rise
of a new species?
Answer :
Following factors could
lead to the rise of new species:
(a) Changes in gene
frequency in small breeding isolated populations.
(b) Natural selection
(c) Changes in number of
chromosome.
11. Will geographical isolation be a major factor in the speciation of
self-
Answer :
No, because geographical
barrier do not allow breeding between such individuals of a population which
reproduce sexually. Moreover, asexually reproducing organism pass on the
parental DNA to offspring which gives no chance of speciation.
12. Will geographical isolation be a major factor in the speciation of
an organism that reproduces asexually? Why or why not?
Answer :
Yes, due to geographical
isolation, the two populations are separated. The levels of gene flow between
them will decrease. The isolated population will breed with local population
resulting in entry of isolated population into new population.
13. Give an example of characteristics being used to determine how
close two species are in evolutionary terms.
Answer :
Analysis of the organ
structure in fossils allows us to make estimates of how far evolutionary
relationships go. For example, presence of feather in some fossils dinosaurs
indicate the birds are closely related to reptiles.
14. Can the wing of a butterfly and the wing of the bat be considered
homologous organs?
Answer :
No, though the function
of wing in both the cases in same but their structural plan and origin in
different.
15. What are fossils?
What do they tell us about the process of evolution?
Answer :
Preserved traces if
living organisms are called fossils found closer to the surface of earth are
more recent in origin than the fossils we find in deeper layers. Fossils also
help us to find evolutionary relation between organisms.
16. 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 :
All humans are a single
species Homo sapiens which originated in Africa. Some of our ancestors left
Africa, while others stayed on. Those who migrated slowly spread across the
planets.
17. In evolutionary terms, can we say which among bacteria, spiders,
fish and chimpanzees have a ‘better’ body design? Why or why not?
Answer :
Bacteria have better body
design because it has so much variation to adjust in different climatic
condition.
18. 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
Answer : (c)
TtWW
19. 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.
Answer : (d)
all of the above
20. 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.
21. 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, since two copies of
traits are inherited from parents, one from mother and the other form father.
Unless we know the nature of these two variants of traits we cannot tell which
is dominant and which is recessive. Recessive traits appear when both the
parents contribute recessive allele. From this statement we can only presume
are that both parents are contributing recessive allele.
22. How are the areas of study- evolution and classification
interlinked?
Answer :
When we classify organism
we look for similarities among organism which allows us to group them. Based on
these principles we can work out the evolutionary relationship to the species.
23. Explain the terms analogous and homologous organs with examples.
Answer :
Analogous organs: Such
organs which perform similar function but are different in structure and
origin. Example- Wings of birds and wings of insects. Homologous organs: Such
organs which may have different functions but similar structure and origin.
Example- fore arm of frog, lizard and bird.
24. Outline a project which aims to find the dominant coat colour in
dogs.
Answer :
Dogs have a variety of
genes that govern coat colour. There are at least eleven identified gene series
(A, B, C, D, E, F, G, M, P, S, T) that influence coat colour in dog.
A dog inherits one gene from each of its parents. The dominant gene gets expressed in the phenotype. For example, in the B series, a dog can be genetically black or brown.
Let us assume that one
parent is homozygous black (BB), while the other parent is homozygous brown
(bb)
In this case, all the offspring will be heterozygous (Bb).
All the offspring will be black since black (B) is dominant. However, they will have both B and
b alleles.
If such heterozygous pups
are crossed, they will produce 25% homozygous black (BB), 50% heterozygous
black (Bb), and 25% homozygous brown (bb) offspring.
25. Explain the importance of fossils in deciding evolutionary
relationship.
Answer :
An organism's remains
from its time on Earth are called fossils. They stand in for the ancestors of
modern-day vegetation and animals. They offer proof of evolution by exposing the traits of extinct organisms and the modifications made to them to create the current entities. This example will help us illustrate the significance of
fossils in determining evolutionary history. Some dead invertebrates were buried in the earth there about 100 million years ago. The sediment
turned into sedimentary rock as more sediment collected on top of it. The
bodies of some dinosaurs that perished there millions of years later were
interred on top of the sedimentary rock. Mud
26. What evidence do we have for the origin of life from inanimate
matter?
Answer :
J.B.S. Haldane, a British
scientist, proposed that basic inorganic molecules were the ancestors of life.
According to his theory, the planet was a heated gaseous mass that contained
components like carbon, hydrogen, nitrogen, and oxygen when it originated.
Water (H20), carbon dioxide (C02), methane (CH4),
ammonia (NH3), and other molecules were created by the combination
of these elements.
Simple organic molecules like sugars, fatty acids, amino acids, and others were
created as the earth's surface gradually cooled after water formed and
inorganic molecules interacted with one another. The energy for these reactions
was provided by solar radiations, lightning, volcanic eruptions, etc.
This was proved by the experiment of Stanley L. Miller and Harold C. Urey in
1953. They took a mixture of water (H20), methane (CH4),
27. 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 arise either
because of errors in DNA copying or as a result of sexual reproduction. Due to
sexual reproduction genetic variability increases in the population from one
generation to another. This happens due to the fact that sexually reproducing
organism inherits half the genes from each parent. These variations are very
important for the process of evolution.
28. 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 been different kinds of
advantages. However, when a drastic change occurs in environment only those
organisms in the population will survive which have an advantageous variation
in that population to survive in changed environment.
29. How is the equal genetic contribution of male and female parents
ensured in the progeny?
Answer :
Equal contribution of
male and female parents is ensured in progeny during sexual reproduction. Each
trait of progeny is determined by a pair of alleles and gametes of male and
female contain one allele. Each allele pairs during fertilisation combine together
to determine traits. Thus, the traits of progeny are determined by equal genes
from male and female.
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