NCERT Solutions for Class 10 Science Chapter 9 - Heredity And Evolution

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Answer:

The exchange of genetic material takes place only in sexual reproduction where two different gametes fuse with each other and give rise to a new organism.

Hence, the correct answer is option (c).

Answer:

In the given cross, pink flowering plants have two dissimilar forms of the gene controlling flower color. So, on selfing of two pink flowers (Rr), red (RR), pink(Rr), and white (rr) flowers are obtained in the ratio 1:2:1.

Hence, the correct answer is option (b).

Answer:

In a cross between two organisms differing in one pair of contrasting traits, F₁ hybrid shows only one of the parental traits, and this trait is called the dominant trait. Similarly, in the question, since the only tall trait is expressed in the progeny resulting from a cross between a tall plant and a short pea plant, tallness is the dominant trait.

Hence, the correct answer is option (a). 

Answer:

Hormones and enzymes are made up of proteins and the formation of any particular protein.  It is also controlled by a particular gene.  Fat formation does not depend on genes. Every protein enzyme and hormone is controlled by a specific gene whereas fats are not controlled by genes. 
Hence, the correct answer is option (d).

Answer:

From the cross between a round, green seeded pea plant (RR yy) and wrinkled, yellow seeded pea plant, (rr YY),

Parents                         RRyy                               x                              rr YY
                                   Round and green                                     Wrinkled and yellow
Gametes                         Ry                                                                      rY

F₁ generation              RrYy
                                Round and yellow seed

F₁ generation plants will produce round and yellow seeds.

Hence, the correct answer is option (a).

 

Answer:

Human males have 22 pairs of autosomes and one mismatched pair of sex chromosomes- one normal-sized X chromosome and the other short Y chromosomes.

Hence, the correct answer is option (c).

Answer:

In humans, the sex of the child is determined by the sex chromosome inherited in the zygote from the father. A human male has X and Y sex chromosomes. If a zygote receives X chromosome from the father, it will develop into a female and if a zygote receives Y chromosome from the father, it will develop into a male.

Hence, the correct answer is option (b). 

Answer:

In humans, females produce eggs with X chromosome whereas males produces sperms with either X or Y chromosome. If a zygote receives X chromosome from father, it inherits X chromosome from mother. Thus, a zygote with XX will develop into a girl child.

Hence, the correct answer is option (b).

Answer:

Reduction in weight of the organism due to starvation do not bring any change in DNA of the gamete so, it is not genetically controlled. Out of the four statements, statement (b) is incorrect.

Hence, the correct answer is option (b).

Answer:

Gametes or sex cells are the cells involved in sexual reproduction. These gametes fuse to form a zygote which develops into a new organism. So, any change in the DNA or chromosome numbers of the gametes will be transmitted to the new organism. If this new organism with inherited changes in DNA or chromosome number may not reproduce with the existing members, this will be considered a new species.

Hence, the correct answer is option (a).

Answer:

The results of selfing F₁ plants with round and yellow seeds (RrYy) are as follows:



The new combinations of characters in F₂ progeny are round and yellow seeds and wrinkled and green seeds.

Hence, the correct answer is option (b).

Answer:

Homologous structures are those structures which have the common origin. Among the given vegetables, carrot and radish are the roots modified for storage of food, potato is the stem modified for storage of food and tomato is a fruit. So, carrot and radish are the examples of homologous structures.

Hence, the correct answer is option (c).

Answer:

The tendrils of a pea plant are leaflets modified into wire-like structures that help the plant cling to support and climb on it. Phylloclade of Opuntia is a green flattened stem with leaves modified into spines so as to reduce the loss of water by transpiration. Since both the plants, tendrils, and spines have a common origin but perform different functions. So, they are homologous structures.

Hence, the correct answer is option (a).

Answer:

Fossils found closer to the surface are more recent than the fossils found in deeper layers. 

Hence, the correct answer is option (b).

Answer:

Variations are produced due to inaccuracy in DNA copying mechanisms and sexual reproduction. All variations in a species do not confer equal survival advantages. So, the statement given as option (a) is not true for variation.

Hence, the correct answer is option (a).

Answer:

An organism receives DNA from both the parents so, the traits are influenced by the both maternal and paternal DNA.

Hence, the correct answer is option (c).

Answer:

Species is the lowest group in the hierarchy of classification. It is a group of individuals that share common characteristics and are capable of interbreeding. Thus, any two individuals of a species share the maximum numbers of related or common characters.

Hence, the correct answer is option (a).

Answer:

According to the evolutionary theory, the accumulation of variations (resulting from errors in DNA copying and sexual reproduction) over several generations along with the operation of natural selection leads to the formation of new species.

Hence, the correct answer is option (b).

Answer:

The size of the body of an organisms increases or decreases based on the availability of the food and results from the changes in the non-reproductive tissues. So, these changes cannot be passed on to the next generation. So, it is an acquired character.

Hence, the correct answer is option (c).

Answer:

An organism inherits two copies of each chromosome, one each from the male and female parents. The two forms of a gene controlling a character (two versions of a trait) are present at the same location on the two copies of one of the chromosomes. At the time of gamete formation, when a chromosome pair segregate and move to different gametes, two forms of a gene also segregate, each gamete receiving one copy of a chromosome along with one form of a gene. When these gametes from two parents fuse, the two copies of the same chromosome along with the two forms of a gene are also brought together in the organism of the next generation.

Hence, the correct answer is option (a).

Answer:

A gene is a segment of DNA that codes for a protein. An organism has a number of genes present on the different chromosomes and each occupies a specific location of a particular chromosome. So, out of given four statements, statements (i) and (iii) are the characteristics of genes.

Hence, the correct answer is option (b).

Answer:

The ratio  of pure tall plants (TT) to short plants (tt) is 1:1.

Hence, the correct answer is option (c).

Answer:

In humans, a gamete has one sex chromosome either X or Y. So, a zygote formed from the fusion of two gametes has two sex chromosomes or a pair of sex chromosomes (XX or XY).

Hence, the correct answer is option (a).

Answer:

Charles Darwin formulated the theory of evolution of species by natural selection based on his observations on the variety of life during his sea voyage to islands.

Hence, the correct answer is option (b).

Answer:

Dinosaurs were reptiles. The possible explanation for the given information that some dinosaurs had feathers but they could not fly and birds have feathers that help them fly, is that feathers in dinosaurs start as providing insulation in cold weather and later they become useful for flight in birds. So, in the context of evolution, this means that birds have evolved from reptiles.

Hence, the correct answer is option (d).

Answer:

Sex of a newborn in humans is genetically determined, that is, genes inherited from the parents determine the sex of a baby. If a newborn inherits one X chromosome from mother and X chromosome from father, this newborn will become a girl and if a newborn inherits one X chromosome from mother and Y chromosome from father, this newborn will become a boy.

Answer:

Mothers have two X chromosomes as sex chromosomes so, they produce eggs with X chromosome. All of her children (both girl and boy) receive X chromosome from their mother. So, genetic combination of mothers do not play a significant role in determining the sex of a new born.

Answer:

Important features of fossils that help in the study of evolution:

• The fossils can be used to determine their age and the time period during which they lived.
• The fossils provide information about morphology and anatomy of the past organisms which can be used to establish their relationship with the present and past organisms.
• They provide tangible, physical evidence of ancient life and has provided the basis of the theory of evolution.

Answer:

Human females have a pair of X chromosomes as sex chromosomes in addition to 22 pairs of homologous chromosomes (autosomes). During gamete formation, two X chromosomes segregate to different gametes. So, all gametes (eggs) in human females have an X chromosome in addition 22 autosomes.

Answer:

In human beings, males possess two sex chromosomes (X and Y) so they produce two types of male gametes - 50%  sperms with X chromosome and 50% sperms with Y chromosome. So, the sex of the child is determined by the sex chromosome present in the male gamete or sperm. Since the ratio of male gametes containing X chromosome and those containing Y chromosome is 50 : 50, the statistical probability of male or a female infant is also 50 : 50.

Answer:

Answer:

Homologous structures are those structures which have a common basic structure but perform different functions. For example, forelimbs of reptiles, amphibians and mammals. Yes, homologous structures always have a common ancestor from which they have evolved along different directions due to adaptations to different needs.

Answer:

Yes, the occurrence of diversity of animals on earth does suggest their diverse ancestry. Because common ancestry may greatly limit the extent of diversity. As many of these diverse animals are inhabiting the same habitat, their evolution by geographical isolation and speciation is also not likely. Thus, a common ancestry for all the animals is not the likely theory.

Answer:

Answer:

Mendel chose the pea plant for his experiments because of the following reasons:

• This plant can be easily grown.
• This plant has a short life cycle and produces a large number of seeds.
• It can self-fertilize.
• It has easily distinguishable contrasting traits.
• Because of its large flower, it can be easily crossed in a controllable manner.

Answer:

In humans, women produce one type of eggs (all with X chromosome) and men produce two types of sperms - 50% with X chromosome and 50% with Y chromosome. All the children of a woman receive X chromosome from her but second sex chromosome which is received from father, can be X or Y. So, the sex is determined by the sex chromosome present in the sperms of the father. If a woman has only daughters, it means father has contributed sperm with X chromosome.

Answer:

Yes, geographical isolation of individuals of a species lead to formation of a new species. Suppose two sub-populations of beetle living in a mountain become separated by a river and there is very low gene flow between them. Over generations, due to the processes of genetic drift and natural selection, these two populations of beetles become different from each other and they are unable to reproduce with each other even if they happen to meet. Slowly the separated individuals will reproduce among themselves and generate new variations. Continuous accumulation of those variations through a few generations may ultimately lead to the formation of a new species.

Answer:

This is difficult to state that organisms with complex body plan like humans are more evolved than the organisms with simpler body plan like bacteria. If progressive trend in evolution is the emergence of more and more complex body designs, human beings are certainly more evolved than bacteria. But on considering the totality of life characteristics into account, it is hard to label either organism as evolved. Because organisms older designs are not inefficient. Many of the older and simpler designs still survive e.g.,  the simplest life forms, bacteria inhabit the most inhospitable habitats like hot springs, deep-sea thermal vents and the ice in Antarctica. So, human beings are not the pinnacle of evolution, but simply yet another species in the teeming spectrum of evolving life.

Answer:

All the human races like Africans, Asians, Europeans, Americans and others share the following characteristics:

• Common body plan, structure, physiology and metabolism.
• Constant chromosome number
• Common genetic blue print
• Freely inter-breeding

Answer:

Answer:

Acquired characters are those characters that an organism gets during its lifetime. These characters do not bring any change in the DNA of germ cells so these characters are not inherited. Acquired traits are the changes that occur in non-reproductive tissues, thus they cannot be passed on to DNA of germ cells. Hence, these characters do not produce a change in the genes of germ cells, so they cannot be inherited.
Example: Swimming skills do not have any genetic changes in the individual who knows it. So it cannot pass from one generation to another as genetic code is the only way organisms pass information to the next generation.

Answer:

All living organisms existing on earth show immense diversity in size, form, structure and morphological features but at the molecular
level, these organisms exhibit unbelievable similarity. For instance, these organisms are made up of the basic biomolecules like DNA, RNA, carbohydrates, proteins etc. which show remarkable similarity in all of them. DNA in all organisms is made up of same units (nucleotides) and has the same double-helical structure. So, evolution has exhibited a greater stability of molecular structure when compared with morphological structures.

Answer:

(a) Parents -                RRYY           $\times$              RRYY
                             Round, yellow                   Round, yellow
Gametes -                     RY                                     RY
Progeny -                        RRYY
                                     Round, yellow

(b)  Parents -              RrYy                 $\times$            RrYy
                              Round, yellow                    Round, yellow

Gametes -              RY, rY, Ry, ry                        RY, rY, Ry, ry
 

Answer:

Parents -                     RRYY                  $\times$              rryy
                              Round, yellow                        Wrinkled, green

Gametes -                        RY                                           ry

F₁-                          RrYy                      $\times$                         RrYy
                             Round, yellow                                     Round, yellow

Answer:

F₁-                          RrYy                      ×$\times$                        RrYy
                             Round, yellow                                    Round, yellow
 

Answer:

Genes present on the chromosomes control characters or traits. A gene controls a character and has two or more forms and one form may be dominant over the other. An individual has two similar or dissimilar forms of a gene controlling a trait, one inherited from each parent. The two forms of a gene separate during gamete formation so that each gamete has only one form. These two forms of a gene are brought together in the zygote when gametes fuse at the time of fertilisation.

Answer:

The reason for the appearance of new combinations in the F2 generation is the Law of Independent Assortment which states that when two pairs of traits are combined in a hybrid, one pair of character segregates independent of the other pair of character.
The two or more genes are inherited independent of each other and they recombine in the zygote to form new combinations in F2 generation. For example, when a tall pea plant with round seeds is crossed with a short pea plant with wrinkled seeds, the gene controlling plant height (tall/short) segregate independent of the gene controlling seed shape (round/wrinkled) and they recombine in the zygote to form new combinations (tall and wrinkled seeds and short and round seeds).