NCERT Grade 10-Heredity and Evolution-Answers

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1.     (c) TtWW

2.    (d) all of the above

3.    (a) a Chinese school boy.

4.    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 can not 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.

5.     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.

6.     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.


8.    (i) Study of fossils allow us to make estimates of how far back evolutionary
relationship go between organisms.

(ii) Study of age of fossils allows us to know which organisms evolved earlier and which later.

9.    The evidence was given by Stanley L. Miller and Harold C. Urey in 1953. They
assembled an atmosphere similar to that thought to exist on early earth over water. This was maintained by them at a temperature just below 100 degree Celcious and sparks were passed through the mixture of gases to stimulus lightening. At the end of week, they found that 15% of the carbon had been converted to simple compounds of carbon including amino acids which make up protein molecules.

10.   Variations arise either because of errors in DNA copying or as a result of sexual
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.

11.    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.

12.   Equal contribution of male and female parents is ensured in progeny during sexual 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.

13.   Trait B.

14.   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.

15.   In Monohybrid cross of Mendel between tall and dwarf pea plant, all progeny in Fl 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.

16.   When a pea plant having round green seeds is crossed with a pea plant having wrinkled yellow seeds in Fl 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.

17.   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 0 blood group from mother as well as father.

18.   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.

19.   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.

20.  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.

21.  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.

22.  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.

23.  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.

24.  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.

25.  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.

26.  No, though the function of wing in both the cases in same but their structural plan and origin in different.

27.  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.

28.  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.

29.  Bacteria have better body design because it has so much variation to adjust in different climatic condition.



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