(Chapter – 8) (How Do Organisms Reproduce?)
(Class – X)
Question 1:
What is the importance of DNA copying in reproduction?
Answer
1:
DNA
(Deoxyribonucleic acid) is the genetic
material found
in the chromosomes, which
are present in the nucleus of a cell. The DNA is the information site for making proteins and each specific type of protein
leads to a specific type of body design.
Thus,
it is the DNA molecule
that determines the body design of an individual. Therefore, it can be concluded that it is the DNA that gets transferred from parents
to offsprings and makes them look similar.
Question
2:
Why is variation beneficial to the species but not necessarily for the individual?
Answer 2:
Variations are beneficial to the species than individual because sometimes
for a species, the environmental conditions
change so drastically that their survival
becomes difficult. For example, if the temperature of water increases
suddenly, then most of the bacteria living in that water would die. Only few variants that are resistant
to heat would be able to survive.
However, if these variants were not there, then the entire
species of bacteria would have been destroyed.
Thus, these variants help in the survival
of the species. However, all variations are not necessarily beneficial for the individual organisms.
Question 1:
How does binary fission differ from multiple
fission?
Answer 1:
In binary fission,
a single cell divides into two equal halves. Amoeba and Bacteria divide by binary
fission.
Binary fission in Amoeba
In multiple fission,
a single cell divides
into many daughter
cells simultaneously. Amoeba
and Plasmodium
divide by multiple
fission.
Multiple fission in Plasmodium
Question 2:
How will an organism be benefited if it reproduces through
spores?
Answer 2:
There are many advantages, if an organism reproduces through
spores.
Advantages of spore formation:
Ø Large numbers of spores
are produced in one sporangium.
Ø Spores are distributed easily by air to far-off places to avoid competition at one place.
Ø Spores are covered by thick walls to prevent
dehydration under unfavourable conditions.
Question
3:
Can you think
of reasons why more complex organisms cannot give rise to new individuals through regeneration?
Answer 3:
Simple organisms such as Hydra and Planaria are capable
of producing new individuals through the process of regeneration. The
process of regeneration involves
the formation of new organisms
from its body parts.
Simple organisms can utilize
this method of reproduction as their entire body is made of similar kind of cells in which any part of their body can be formed by growth
and development.
However, complex organisms have organ-system level of organization. All the organ systems of their body work together as an interconnected unit. They can regenerate their lost body parts such as skin, muscles, blood, etc. However, they cannot give rise
to new individuals through regeneration.
Question 4:
Which of the following is a plant hormone?
(a)
Insulin
(b)
Thyroxin
(c)
Oestrogen
(d)
Cytokinin
Answer 4:
(d)
Cytokinin is a plant hormone.
Question
5:
Why is DNA copying
an essential part of the process of reproduction?
Answer 5:
DNA (Deoxyribonucleic acid) copying is an essential
part of reproduction as it passes genetic information
from parents to offspring. It determines the body design
of an individual. The reproducing cells produce a copy of their DNA through some chemical reactions and result in two copies of DNA. The copying of DNA always takes place along with the creation of additional cellular structure. This process
is then followed by division of a cell to form two cells.
Question 1:
How is the process of pollination different from fertilization?
Answer
1:
Pollination is the process of transfer of pollens from anther to stigma. It occurs with the help of certain
pollinators such as air, water,
birds, or some insects.
Fertilization, on the other hand, is the fusion of the male and female gametes. It occurs inside the ovule and leads to the formation of zygote.
Question
2:
What is the role of the seminal
vesicles and the prostate
gland?
Answer
2:
The secretions from seminal
vesicles and prostate
glands lubricate the sperms and provide a fluid medium for easy transport of sperms. Their secretion
also provides nutrient in the form of fructose, calcium,
and some enzymes.
Question
3:
What are the changes
seen in girls at the time of puberty?
Answer
3:
Secondary sexual characteristics in girls:
•
Increase in breast size and darkening
of skin of the nipples
present at the tips of the breasts.
•
Appearance of hair in the genital
area.
•
Appearance of hair in other areas
of skin like underarms, face, hands, and legs.
•
Increase in the size of uterus
and ovary.
•
Beginning of menstrual
cycle.
•
More secretion of oil from the skin, which results in the appearance of pimples.
Question 4:
How does the embryo get nourishment inside
the mother’s body?
Answer 4:
The embryo
develops inside the mother’s body for about
nine months. Inside the uterus, the outer tissue surrounding the embryo develops finger-like projections called villi.
These villi are surrounded by uterine tissue and maternal
blood. They provide a large surface area for exchange of oxygen
and nutrients. Also, there is a special
tissue called placenta, which is embedded in the uterine wall. The embryo receives
the oxygen and nutrients from the mother’s blood via the placenta.
The waste materials
produced by the embryo are also removed through
the placenta.
Question 5:
If a woman is using a copper−T, will it help in protecting her from sexually transmitted
diseases?
Answer 5:
No. Using a copper-T
will not provide a protection from sexually transmitted diseases,
as it does not prevent the entry of semen. It only prevents
the implantation of the embryo in the uterus.
Question 1:
Asexual reproduction takes place through budding
in
(a) amoeba.
(b) yeast.
(c)
plasmodium.
(d) leishmania.
Answer 1:
(b) Asexual
reproduction takes place through
budding in yeast.
Question 2:
Which of the following
is not a part of the female reproductive system in human beings?
(a) Ovary
(b) Uterus
(c) Vas deferens
(d) Fallopian tube
Answer 2:
(c) Vas deferens is not a part of the female reproductive system in human beings.
Question 3:
The anther contains
(a) sepals.
(b) ovules.
(c) carpel.
(d) pollen grains.
Answer 3:
(d) The anther contains
pollen grains.
Question
4:
What are the advantages of sexual
reproduction over asexual reproduction?
Answer 4:
Advantages of sexual reproduction:
Ø
In sexual reproduction, more variations are produced.
Thus, it ensures
survival of species in a population.
Ø The new formed individual has characteristics of both the parents.
Ø
Variations are more viable
in sexual mode than in asexual
one. This is because
in asexual reproduction,
DNA has to function
inside the inherited cellular apparatus.
Question 5:
What are the functions
performed by the testis
in human beings?
Answer 5:
The testes are the male reproductive organs that are located outside
the abdominal cavity within a pouch called
scrotum.
Functions of testes:
Ø Produce sperms
Ø
Produce a hormone
called testosterone, which brings about secondary
sexual characters in boys.
Question 6:
Why does menstruation occur?
Answer 6:
Menstruation is a process
in which blood and mucous flows out
every month through the vagina. This process occurs
every month because one egg is released
from the ovary
every month and at the same time, the uterus (womb) prepares itself to receive
the fertilized egg. Thus, the inner lining
of the uterus gets thickened
and is supplied
with blood to nourish the embryo.
If the egg does not get fertilised, then the lining of the uterus breaks down slowly and gets released
in the form of blood and mucous from the vagina.
Question 7:
Draw a labelled
diagram of the longitudinal section of a flower.
Answer 7:
Question 8:
What are the different methods of contraception?
Answer 8:
The contraceptive methods can be broadly
divided into the following
types:
Ø
Natural method: It involves avoiding
the chances of meeting of sperms
and ovum. In this method, the sexual act is avoided from day 10th to 17th of the menstrual cycle because
during this period, ovulation is expected and therefore, the chances of fertilization
are very high.
Ø
Barrier method: In this method,
the fertilization of ovum and sperm is prevented with the help of barriers. Barriers are available
for both males and females. Condoms are barriers made of thin rubber that are used to cover penis in males and vagina in females.
Ø
Oral contraceptives: In this method, tablets
or drugs are taken
orally. These contain small doses of hormones that prevent the release
of eggs and thus fertilization cannot occur.
Ø
Implants and surgical
methods: Contraceptive devices such as the loop or Copper-T are placed in uterus to prevent pregnancy. Some surgical methods can also be used to block the gamete transfer.
It includes the blocking
of vas deferens to prevent the transfer of sperms known as vasectomy. Similarly,
fallopian tubes of the female can be blocked so that the egg will not reach the uterus known as tubectomy.
Question
9:
How are the modes for reproduction different in unicellular and multicellular organisms?
Answer 9:
In unicellular organisms, reproduction occurs by the division
of the entire
cell. The modes of reproduction
in unicellular organisms
can be fission, budding, etc. whereas in multicellular organisms, specialised reproductive organs are present. Therefore, they can reproduce by complex reproductive methods
such as vegetative propagation, spore formation, etc. In more
complex multicellular organisms such as human beings
and plants, the mode of reproduction is sexual reproduction.
Question 10:
How does reproduction help in providing stability to populations of species?
Answer 10:
Living organisms reproduce for the continuation of a particular species.
It helps in providing stability to the population of species
by producing a new individual that resembles the parents.
This is the reason why cats give birth to only cats or dogs give birth to only dogs. Therefore, reproduction provides stability to populations of dogs or cats or any other species.
Question
11:
What could be the reasons
for adopting contraceptive methods?
Answer 11:
Contraceptive methods
are mainly adopted
because of the following reasons:
(i)
To prevent unwanted pregnancies.
(ii)
To control population rise or birth rate.
(iii)
To prevent the transfer of sexually
transmitted diseases.
(Chapter – 9) (Heredity
and Evolution)
(Class – X)
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 1:
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.
Question
2:
How does the creation
of variations in a species
promote survival?
Answer 2:
Sometimes for a species, the environmental conditions change so drastically that their survival becomes difficult.
For example, if the temperature of water increases
suddenly, most of the bacteria living in that water would die. Only few variants
resistant to heat would be able to survive.
If these variants were not there, then the entire
species of bacteria would have been destroyed. Thus, these variants
help in the survival of the species.
However, not all variations are useful. Therefore, these are not necessarily beneficial for the individual organisms.
Question 1:
How do Mendel’s experiments show that traits
may be dominant or recessive?
Answer 1:
Mendel selected true breeding tall
(TT) and dwarf (tt) pea plants.
Then, he crossed
these two plants. The seeds formed after fertilization were grown and these plants that were formed represent the first filial or F1 generation. All the F1 plants obtained were tall.
Then, Mendel self-pollinated the F1 plants and observed
that all plants obtained in the F2 generation were not tall. Instead,
one-fourth of the F2 plants
were short.
From this experiment, Mendel concluded
that the F1 tall plants were not true breeding. They were carrying
traits of both short height and tall height. They appeared tall only because the tall trait is dominant over the dwarf trait.
Question 2:
How do Mendel’s experiments show that traits
are inherited independently?
Answer
2:
Mendel crossed pea plants having round green seeds (RRyy) with pea plants having wrinkled yellow seeds (rrYY).
An example of dihybrid
crosses
Since the F1 plants
are formed after crossing
pea plants having green round seeds and pea plants having yellow wrinkled
seeds, F1 generation will have both these characters in them. However, as we know that yellow
seed colour and round seeds are dominant characters, therefore, the F1 plants will have yellow
round seeds.
Then this F1 progeny was self-pollinated and the F2 progeny was found to have yellow round seeds, green round seeds, yellow wrinkled seeds, and green wrinkled
seeds in the ratio of 9:3:3:1.
Independent inheritance of two different
traits
In the above cross,
more than two factors
are involved, and these are independently inherited.
Question 3:
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 3:
No. This information is not sufficient
to determine which of the traits − blood group A or O − is dominant. This is because
we do not know about the blood group of all the progeny. Blood group A can be genotypically AA or AO. Hence, the information is incomplete to draw any such conclusion.
Question 4:
How is the sex of the child determined in human beings?
Answer 4:
In human beings, the females have two X chromosomes and the males
have one X and one Y chromosome. Therefore, the females are XX and the males are XY.
The gametes, as we know, receive
half of the chromosomes. The male gametes
have 22 autosomes and either X or Y sex chromosome.
Type of male gametes:
22+X OR 22+ Y.
However, since the females
have XX sex chromosomes, their gametes
can only have X sex chromosome.
Type of female gamete:
22+X
Sex determination in humans
Thus, the mother provides
only X chromosomes. The sex of the baby is determined by the type of male gamete (X or Y) that fuses with the X chromosome of the female.
Question 1:
What are the different
ways in which individuals with a particular trait may increase in a population?
Answer 1:
Individuals with a particular trait
may increase in a population as a result
of the following:
(i) Natural selection: When that trait offers
some survival advantage.
(ii) Genetic drift: When some genes governing that trait become common
in a population.
(iii) When that trait gets acquired during
the individual’s lifetime.
Why are traits acquired
during the life-time
of an individual not inherited?
Answer 2:
This happens because an acquired trait involves
change in non-reproductive tissues (somatic cells)
which cannot be passed on to germ cells
or the progeny. Therefore, these traits cannot
be inherited.
Why are the
small numbers of surviving
tigers a cause
of worry from the point of view
of genetics?
Answer 3:
Small numbers
of tigers means that fewer variations in terms of genes are available. This means that when these tigers reproduce, there are less chances
of producing progeny
with some useful variations. Hence, it is a cause of worry from the point
of view of genetics.
Question 1:
What factors
could lead to the rise of a new species?
Answer 1:
Natural selection, genetic drift and acquisition of traits during the life time of an individual can give rise to new species.
Question 2:
Will geographical isolation be a major factor in the speciation of a self-pollinating plant species? Why or why not?
Answer 2:
Geographical isolation can prevent
the transfer of pollens among different plants. However, since the plants are self-pollinating, which means that the pollens are transferred from the anther of one flower to the stigma of the
same flower or of another flower of the same plant, geographical isolation cannot
prevent speciation in this case.
Question 3:
Will geographical isolation
be a major factor in the speciation of an organism that reproduces asexually? Why or why not?
Answer 3:
Geographical isolation prevents gene flow between populations of a species whereas asexual reproduction generally involves only one individual. In an asexually reproducing organism, variations can occur only when the copying
of DNA is not accurate. Therefore, geographical isolation cannot prevent
the formation of new species
in an asexually reproducing organism.
Question 1:
Give an example of characteristics being used to determine how close two species are in evolutionary terms.
Answer 1:
The presence of feathers
in dinosaurs and birds indicates that they are evolutionarily related. Dinosaurs had feathers
not for flying but instead these
feathers provided insulation to these warm-blooded animals.
However, the feathers in birds are used for flight. This
proves that reptiles
and birds are closely related and that the evolution of wings started in reptiles.
Question
2:
Can the wing of a butterfly and the wing of a bat be considered homologous organs?
Why or why not?
Answer 2:
Wings of a butterfly are composed
of membrane, while wings of a bat are composed of bony skeleton.
Hence, these are not homologous organs rather
analogous organs.
Question 3:
What are fossils? What do they tell us about the process
of evolution?
Answer 3:
Fossils are the remains
of organisms that once existed on earth. They represent
the ancestors of plants
and animals that are alive today.
They provide evidences
of evolution by revealing the characteristics of the past organism and the changes that have occurred in these organisms to give rise to the present organisms.
Question 1:
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 1:
A species is a group of organisms
that are capable of interbreeding to produce a fertile offspring. Skin colour,
looks, and size are all variety of features present
in human beings. These features are generally
environmentally controlled. Various human races are formed based on these features.
However, there is no biological basis to this concept
of races.
Therefore, all human beings are
a single species
as humans of different colour, size, and looks are capable of reproduction and can produce a fertile offspring.
Question
2:
In evolutionary terms, can we say which among bacteria, spiders, fish and chimpanzees
have a ‘better’
body design? Why or why not?
Answer 2:
Evolution cannot always
be equated with
progress or better
body designs. Evolution simply creates more complex body designs.
However, this does not mean that the simple body designs are inefficient. In fact, bacteria having a simple body design are still the most cosmopolitan organisms
found on earth. They can survive hot springs, deep sea, and even freezing environment.
Therefore, bacteria, spiders,
fish, and chimpanzees are all different
branches of 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
Answer 1:
(c) The genetic make-up
of the tall parent can be depicted
as TtWW
Since all the progeny bore violet flowers, it means that the tall plant having violet
flowers has WW genotype for violet
flower colour.
Since the progeny is both tall and short, the parent plant was not a pure tall plant. Its genotype must be Tt.
Therefore, the cross involved in the given question
is
TtWw × ttww
↓
TtWw − ttww
Therefore, half the progeny
is tall, but all of them have violet
flowers.
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.
Answer 2:
(b)An example of homologous organs is our teeth and an elephant’s tusks.
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 3:
(a) In evolutionary terms, we have more in common
with 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 4:
Let us assume that children with light - coloured eyes can either have LL or Ll or ll genotype. If the children have LL genotype,
then their parents
will also be of LL genotype.
LL × LL
↓
LL
If the children with light-coloured eyes have ll genotype, then their
parents will also have ll genotype.
ll × ll
↓
ll
Therefore, it cannot be concluded whether light
eye colour is dominant or recessive.
Question 5:
How are the areas of study − evolution and classification − interlinked?
Answer 5:
Classification involves
grouping of organism into a formal
system based on similarities in internal and external
structure or evolutionary history.
Two species are more closely
related if they have more characteristics in common. And if two species are more closely
related, then it means they have a more recent ancestor.
For example, in a family, a brother and sister are closely related and they have a recent common ancestor i.e., their parents.
A brother and his cousin are also related but less than the sister and her brother.
This is because
the brother and his cousin have a common ancestor i.e., their grandparents in the second
generation whereas
the parents were from the first generation.
With subsequent generations, the variations make organisms more different
than their ancestors.
This discussion clearly proves
that we classify organisms according to their resemblance which is similar
to creating an evolutionary tree.
Question 6:
Explain the terms analogous and homologous organs with examples.
Answer 6:
Homologous organs are similar in origin (or are embryologically similar) but perform different functions. For example, the forelimbs
of humans and the wings of birds look different externally but their skeletal structure
is similar. It means that their origin is similar (as wings in birds are modifications of forearm) but functions are different - the wings help in flight
whereas human forearm
helps in various activities.
Analogous organs, on the other
hand, have different origin
but perform similar functions. For example, the wings of
a bird and a bat are similar in
function but this similarity does not mean that these animals are more closely related.
If we carefully
look at these structures, then we will find that the wings of a bat are just the folds of skin that are stretched between its fingers whereas
the wings of birds are present
all along the arm. Therefore, these organs
are analogous organs.
Question 7:
Outline a project which aims to find the dominant coat colour
in dogs.
Answer 7:
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).
bb
|
BB
|
||
B
|
B
|
||
b
|
Bb
|
Bb
|
|
b
|
Bb
|
Bb
|
|
In this case, all the offsprings will be heterozygous (Bb).
Since black (B) is dominant, all the offsprings will be black. 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) offsprings.
B
|
b
|
|
B
|
BB
|
Bb
|
b
|
Bb
|
Bb
|
Question 8:
Explain the importance of fossils
in deciding evolutionary relationships.
Answer 8:
Fossils are the remains
of the organism that once existed
on earth. They represent the ancestors of the plants
and animals that are alive today. They provide
evidences of evolution by revealing the characteristics of the past organisms
and the changes that have occurred in these organisms to give rise to the present organisms. Let us explain
the importance of fossils
in deciding evolutionary history
with the help of the following example.
Around 100 million
years ago, some invertebrates died and were buried in the soil in that area. More sediment accumulated on top of it turning it into
sedimentary rock. At the same place, millions
of years later,
some dinosaurs died and their bodies were buried on top of the sedimentary rock. The mud containing dinosaurs also turned
into a rock.
Then, millions of years later,
some horse-like creatures
died in that area and got fossilized in rocks above the dinosaur
fossils.
Sometime later, due to soil erosion
or floods in that area, the rocks containing horselike fossils are exposed.
If that area is excavated
deeper, then the dinosaur
and invertebrates fossils can also be found. Thus, by digging
that area, scientists can easily predict that horse-like
animals evolved later than the dinosaurs
and the invertebrates.
Thus, the above
example suggests
that the fossils
found closer to the surface
of the earth are more recent ones than the fossils present in deeper
layers.
Question 9:
What evidence
do we have for the origin
of life from inanimate matter?
Answer 9:
A British scientist, J.B.S. Haldane, suggested
that life originated from simple inorganic molecules. He believed that when the earth was formed, it was a hot gaseous
mass containing elements
such as nitrogen, oxygen, carbon,
hydrogen, etc. These elements combined to form molecules like water (H2O), carbon dioxide (CO2), methane
(CH4), ammonia (NH3), etc.
After the formation
of water, slowly
the earth surface cooled and the inorganic molecules interacted with one another in water to form simple organic molecules
such as sugars, fatty acids, amino
acids, etc. 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 (H2O), methane (CH4), ammonia
(NH3), and hydrogen
gas (H2) in a chamber and sparks were passed through
this mixture using two electrodes.
After one week, 15% of the carbon from methane
was converted into amino
acids, sugars, etc. These organic molecules are polymerized and assembled to form protein molecules that gave rise to life on earth.
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?
Answer 10:
In sexual reproduction, two individuals having different
variations combine their DNA to give rise to a new individual. Therefore, sexual
reproduction allows more variations, whereas in asexual reproduction, chance variations
can only occur when the copying of DNA is not accurate.
Additionally, asexual reproduction allows very less variations
because if there are more variations, then the resultant
DNA will not be able to survive inside the inherited cellular apparatus.
However, in sexual reproduction, more variations are allowed and the resultant
DNA is also able to survive,
thus making the variations viable.
Variation and Evolution: Variants
help the species to survive in all the conditions. Environmental conditions such as heat, light, pests,
and food availability can change suddenly at only one place. At that time,
only those variants
resistant to these conditions would be able to survive. This will slowly lead to the evolution of a better adapted species. Thus, variation helps in the evolution
of sexually reproducing organisms.
Question 11:
How is the equal genetic contribution of male and female
parents ensured in the progeny?
Answer 11:
In human beings, every somatic cell of the body contains 23 pairs of chromosomes. Out of these 23 pairs, the first 22 pairs are known as autosomes
and the remaining one pair is known as sex chromosomes represented as X and Y.
Females have two X chromosomes and males have one X and one Y chromosome. The gamete receives half of the
chromosomes. Therefore,
the male gametes have 22 autosomes and either X or Y chromosome.
The female gamete,
on the other hand, has 22 autosomes
and X chromosome.
During reproduction, the male and female gametes fuse and thus the progeny receives 22 autosomes and one X or Y chromosome
from male parent and 22 autosomes and one X chromosome from the female parent.
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 12:
In species, variations that offer survival
advantages are naturally selected. Individuals adjust to their environments with the help of these
selected variations and consequently these variations are passed on to their progeny.
Evolution of organisms occurs as a result of this natural selection.
However, there
can be some other variations,
which do not offer any survival advantage and arise only accidentally. Such variations in small populations can change the frequency of some genes even if they are not important
for survival.
This accidental change in the frequency
of genes in small populations is referred to as genetic drift.
Thus, genetic
drift provides diversity (variations) without any survival
advantage.
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