CLASS: X-SCIENCE
CHAPTER: HEREDITY AND EVOLUTION
NCERT
IN–TEXT QUESTIONS SOLVED
Q1. If a trait A exists in 10% of a population
of an asexually reproducing species and a trait B ists in 60% of the same
population, which trait is likely to have arisen earlier?
Ans. Trait B is likely to have arisen earlier as it occurs in
more number.
Q2. How does the creation of variations in a
species promote survival?
Ans. Variations increases the adaptability of an organism to its
changing environmental conditions.
Q3. How do Mendel’s experiments show that traits may
be dominant or recessive?
Ans. Mendel took pea plants of two different thuacters i.e.,
tall plants and short plants. The first generation of F1 progeny formed were
all tall. This shows that traits may be either dominant or recessive, there is
no way in between traits obtained.
Q4. How do Mendel’s experiments show that traits are
inherited independently?
Ans. When Mendel crossed pure bred tall pea plants with pure
bred short pea plants, he found that only tall plants were produced in F1
generation. Mendel, further crossed the tall pea plants obtained in F1
generation with dwarf plants and obtained the ratio of Tall: Short plant 3 : 1
in F2 generation. This experiment proved that traits are inherited
independently so other intermediate traits or new traits were formed.
Q5. A man with blood group A niarries 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 dominant? Why or why
not?
Ans. The given information is not enough to tell us which of the
t nits-blood group A or O ‘ is dominant In blood heredi, bood type A is always dominant
and blood type O is always recessive. Here, father's Blood group can be 1AIA
(homozygous) or IAi theterozygous) genotypically, where that of
mother is if. For daughter to be born with blood group O, she must receive i
type gene one each from father and mother. For this father must have
heterozygous IAi blood group and mother must have homozygous blood group ii.
Q6. How the sex of the child determined in
human beings?
Ans. In case of human beings female sex have a pair of
chromosomes (sex) and male sex have a pair of XY sex chromosome. When the
crossing of male and female gametes takes place then the sex of the child
determined as follows:
This
shows that the ratio of male: female sex of the child is same i.e., (1 : 1),
50% possibility of each is seen here.
Q7. at are the different ways in which
individuals with a particular trait may increase in a population?
Ans. The ways in which individual with a particular trait may be
increased a population are:
(a)
If it can survive in the adverse condition i.e., naturally selected.
(b)
It can also be increased by the inheritance.
Q8. Why by are traits acquired during the
life-time of an individual not inherited?
Ans. The traits can be inherited from one generation to the
other only if there is a variation/change in DNA. The traits acquired during
the life-time of an individual may not bring change the genes of DNA.
Q9. Why are the small numbers of surviving
tiger's a cause of worry from the point of view of genetics?
Ans. The small number of tigers are causing a worry for the
genetics because if they become extinct then the genes of this species will be
lost forever. There will be no scope of again getting this species back to life
without their genes.
Q10. What factors could lead to the rise of a
new species?
Ans. The factors which can lead to the rise of a new species are
gene flow, genetic drift, reproductive isolation and natural selection.
Q11. Will geographical isolation be a major
factor in the speciation of a self-pollinating plant species. Why or why not?
Ans. No, geographical isolation cannot he a major factor in the
speciation of self-pollinating plant species. It is because such plants do not
depend on other plants for its further reproduction to be carried out.
Q12. Will geographical isolation be a major
factor in the speciation of an organism that reproduces asexially? Why or why
not?
Ans. No, because the asexually reproducing organisms does not
depend on other organisms for their reproduction.
Q13. Give an e ample of characteristics being
used to determine how close two species are in evolutionary terms.
Ans. Two organisms with similar characteristics have genes with
similar DNA codes. Whereas the organisms with different characteristics will
have different genes, different DNA structures.
Q14. Can the wing of a butterfly and the wing
of a bat he considered homologous organ? Why or why not?
Ans. The wing of butterfly and the wing of a bat cannot be
considered homologous organs because both have different structures but same
function. They have different basic structural design and developmental origin.
They are analogous organs.
Q15. What are fossils? What do they tell u
about the process of evolution?
Ans. Preserved traces of living or dead organisms on solid hard
surface is called fossil. Fossils help us to know the evolution, If a fossil is
found closer to the surface of earth, then it is more recent in origin than the
fossils we find in deeper layers. Fossils, like Archaeopteryx, help us to find
evolutionatzy relation between organisms.
Q16. Why are human beings who look so different
from each other in tens of size, colour and looks said to belong to the same
species?
Ans. Because irrespective differences in characters they have
capacity of interbreeding. Interbreeding is an important criteria to categorize
them as one species.
Q17. In evolutionary terms, we can say which
among bacteria, spiders, fish and chimpanees have a better body design? Why or
why not?
Ans. Evolution shows that body design changed from simple to
complex. Hence, bacteria has the simplest body design a rid chimpanzee has the
most complex and better body design.
QUESTIONS FROM NCERT TEXTBOOK
Q1. A Mendelian experiment consisted of
breeding tall pea plants bean 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)
TTWU1 (b) TT
(c)
T r W W (d) TtWw
Ans. (c) TtWW
Q2. 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,
Ans. (d) all of the above.
Q3. In evolutionary terms, we have more in
common with
(a)
a Chinese
school-boy. (b) a
chimpanzee.
(c)
a
spider, (d)
a bacterium.
Ans. (a) a Chinese school-boy
Q4. 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?
Ans. No, we cannot say that the traits is recessive or dominant
mess we ltnow the nature of the two variants of a trait.
Q5. How are the areas of study-evolution and
lassi ation-interlinked?
Ans. For classification of organisms we generally group the
organisms of same characteristics together and those with different
characteristics are grouped or classified separately. A. set of characteristics
tells about the level of evolution of an organism.
Q6. Explain the terms analogous and homologous
organs with eampies.
Ans. Analogous organs-Organs with different structure and same
function e.g., wings of bird, insects. Homologous organs-Organs which have same
structure but different functions axe called homologous organ e.g., forearm of
lizard, bird and human.
Q7. Outline a project which ems to find the
dominant coat colour in dogs.
Ans. Dominant → WW (white colour)
Q8. Explain the importance of fossils in
deciding evolutionary relcitionships.
Ans. Fossils help us to know the following:
(a)
Fossils help to trace the racial history of organisms.
(b)
They help to measure the geological time,
(c)
Older fossils lie at the depth and young fossils are at the upper surface of the
earth. Complex organisms are present at top and simple organisms are present at
the bottom.
(d)
Fossil like—Archaeopteryx-show the link between two different types of species.
Q9. What evidence do we have for the origin of
life from inanimation?
Ans. Miller and Urey in 1953 assembled an atmosphere similar to
that thought to exist at early period (Gases like ammonia, methane, hydrogen
sulphide) over earth. This was maintained at a temperature just below 100°C and
sparks were passed through the mixture of gases to simulate lighting. At the
end of a week 15% of the carbon (from methane) had been converted to simple
compounds of carbon including amino acids which inalke up protein molecules.
Presence of protein cell membrane correlates with above experiment. This shows
that life originated from inanimate matter.
Q10. Explain how sexual reproduction gives rise
to more viable variations than asexual reproduction. How does this affect the
evolution of those orgciriisms that reproduce se ually?
Ans. Variations are seen more in sexual reproduction than
asexual reproduction because variations occur due to change in DNA coding and
due to sexual reproduction in which two genes from two different sexes Le.,
male and female genes crossing over takes place and hence cause the variation.
Q11. How is the equal genetic contribution of
male and female parents ensured in the progeny?
Ans. By studying the crossing over of genes of male sex and
female sex is as follows:
Q12. Only variations that confer an advantage
to an indivIdual organism population. Do you agree with this statement? Why or
why not?
Ans. No, depending on the nature of variations different
individuals have different kinds of advantages. However, when a drastic change
occurs in environment only those organism in the population will survive which
have an advantageous variation in that population to survive in changed
environment.
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