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Thursday, 29 October 2015

Heredity and Evolution (question -answer)
Q. Why did Mendel chosen pea plant for his experiments?

Answer:   Mendel chose pea plant for his experiments because it is:
(a) Easy to grow (b) Short lifespan (c) Easily distinguishable characters (d) Larger size of flower  (e) Self-pollinated.

Q. What is heredity?

Ans:- Heredity refers to the transmission of characters or traits from the parents to their offspring.

Q. What do you understand by evolution?

Ans:-Evolution is the sequence of gradual changes which takes place in the primitive organisms over million of years in which new species are produced.

Q. What is  a gene?

Ans:- Gene is a small segment of DNA on a chromosome occupying specific position in which is a hereditary determinant or unit of a biological function.

Q. With the help of suitable examples, explain why certain traits cannot be passed on to the next generation. What are such traits called? 

Solution:      The traits which are acquired during the lifetime of a person are called acquired traits. These traits involve changes in non reproductive cells (somatic cells) which are not transferred to germ cells. So, these traits cannot be passed on to the next generation. For example: Learning skills like swimming, dancing, cooking, body building, etc are acquired traits and cannot be passed on to the next generation.

Q. "A trait may be inherited, but may not be expressed." Justify this statement with the help of a suitable example. 
Ans: When a tall plant was crossed with a short plant, the first (F1) generation plants were all tall. But when the F1 generation plants were crossed, the second (F2) generation plants were not all tall: there were both tall and short plants. 

 This shows that the F1 plants had inherited their trait from the short plants but did not express it in the presence of the tallness, and had transferred it to the next generation.

Q. 'It is a matter of chance whether a couple will give birth to a male child or a female child." Justify this statement with the help of a flow chart showing the fusion of sex chromosomes. 

 Ans: Sex is determined at the time of fertilization and the two sexes are produced in approximately equal numbers. A human male has XY sex-chromosomes and produces two types of sperms (heterogametic). Either with X-chromosome or with Y-chromosome.

A human female has XX sex-chromosomes and produce ova of one type (homogametic) all with X-chromosomes.

Parents Male                                   Female

Gametes         X Y                                X

Progeny          XX                                XY

                     Female (50%)           Male (50%)
Q.What are homologous organs? How do they provide evidence in support of evolution?Ans:- Homologous organs are those organs which have the same basic structure and developmental origin but have different functions and appearance.

Homologous organs support evolution:

(i) The similarities of structure and origin of organs indicate that all vertebrates had common ancestors. For example, the forelimbs of humans, whale and bat show structural similarities but functional dissimilarities. Forelimbs in humans used for grasping or holding the things, in whale for swimming and in bat for flying.
(ii) All the organs and systems of the vertebrates show fundamental similarities i.e. homology, which indicate towards common ancestry. Thus, homologous point that organic evolution has taken place.  

Q. What is a retrovirus?

Ans:- A virus having RNA (Ribonucleic acid) as genetic (heredity) material is called Retrovirus. For example, Human immunodeficiency virus (HIV) is a retrovirus.

Q. Who provided the evidence of DNA as a genetic material? Write the names of components of DNA?

Ans:- Griffith, Avery , McLeod and McCarty established that DNA is the genetic material.
Components of DNA: A DNA molecule consists of two polynucleotide chains. Each nucleotide consists of (a) nitrogenous base (Adenine/guanine/Thymine or Cytosine) ,a pentose sugar(deoxyribose) and a phosphate group.

Q.How many types of nitrogenous bases are present in DNA?Name them.
Ans:-In DNA two types of nitrogenous bases are present. These are 
(i)PURINES which are adenine and guanine (ii)PYRIMIDINES which are Thymine and cytosine.

Q.How do embryological studies provide evidence for evolution?
Ans:- The similarities in embryonic development reinforce the idea of evolution from common ancestors. The sequence of embryonic development in different vertebrates shows striking similarities. Notochord and gill clefts appear in the embryos of all vertebrates.

Q.Define evolution. And Describe the contribution of Lamarck?

Ans:- Evolution is the sequence of gradual changes which takes place in the primitive organisms over millions of years in which new species are produced.

Contribution of Lamarck:
(i) Lamarck proposed a theory called “The Theory of inheritance of Acquired Characters” to explain the origin and evolution of species.
(ii) The theory was explained in his book ‘Philosophic Zoologique.

Q. What are transgenic organisms? Which property of DNA is used as a tool in genetic engineering?

Ans:-The organisms that contain a segment of foreign DNA are known as transgenic organisms.The complimentary property of the nucleotides of the most powerful tool in genetic engineering.

Q.Name the two homologous structures in vertebrates. Why are they so called? How do such organs help in understanding an evolutionary relationship?

Ans:  Limbs of birds, reptiles and humans are all the examples of homologous structures in the vertebrates.  They are called so as the basic structure of the limbs is similar. Though it has been modified to perform different functions in various vertebrates.
These are organs which are inherited from a common ancestor. Such a homologous characteristic helps to identify an evolutionary relationship between apparently different species.

Q. What are the different ways in which individuals with a particular trait may increase in a population?
 Ans : The different ways in which individuals with a particular trait may increase in a population, are :

Genetic drift ; Geographical isolation ; Natural selection and Artificial selection

Q.  Why are the small numbers of surviving tigers a cause of worry from the point of view of genetics? 

Ans : If they all die out became extinct, tiger gene will be lost forever and the coming generation will not be able to see tiger at all.

Q. Will geographical isolation be a major factor in the speciation of a self-pollination plant species? Why or why not?

Ans: No, In asexually reproducing organisms pass on the parent DNA to offspring that leaves no chance of speciation

Q. What is the evolutionary significance of the fossil archaeopteryx?

Ans: Archaeopteryx serves as a connecting link between birds and reptiles. It is the fossil evidence to show that birds have evolved from reptiles.

Q. Give the evidence that bird have been evolved from reptile?

Ans: They both lay eggs, have scales on feet and soft anatomy such as musculature, brain, heart.  

Q. What are vestigial organs? Name any two vestigial organs in man and name organ which is vestigial in man but not in birds.
Ans: Organs that are well developed and functional in many organisms and are very much reduced and functionless in other organisms is called vestigial organs. Nictitating membrane in the eye and vermiform appendix attached to the intestine are two such examples of vestigial organs in man. 
Nictitating membrane provides protection of eyes in birds, but in humans it remains as a small fold of skin.

Q.Variation is useful for the survival of species overtime but the variants have unequal chances of survival. Explain the statement.

Ans: If organisms are suited to a particular environment there is chances of survival but  drastic changes in environment could wipe out that population 
(i) If some variations are there, few individuals might survive  
(ii) Depending on whether the variations are useful to the change in the environment some variants survive whereas others do not

Q. a) Why do we see different variety of organisms around us?  b) In which type of reproduction   
(i) Off springs are identical? (ii) Exact similar offspring‘s are not produced? 

Ans: (a) Due to inaccuracies in DNA copying (i) asexual (ii)sexual reproduction

Q. How do species of two isolated sub populations become two different species?

Ans: Together, the processes of genetic drift and natural selection will result in these two isolated sub-populations and thus species of two isolated sub populations become two different species

Q. How does sexual reproduction leads to similarities as well as variations ? 

Ans: Similarities and variations are dependent on the type of allele combination an offspring will get from their parents. If a child get dominant alleles from  father then he will look quite similar to his  father and quit different from his mother. If he got a combination of dominant alleles from both the parents then he will be quite different from both the parents.  

Q.All dead organisms do not leave their fossil records, but in some cases their fossils are formed. How do these fossils records form a direct evidence of past happenings?

Ans:  There are two components to this estimation. One is relative. If we dig into the earth and start finding fossils, it is reasonable to suppose that the fossils we find closer to the surface are more recent than the fossils we find in deeper layers. The second way of dating fossils is by detecting the ratios of different isotopes of the same element in the fossil material.

Q. Evolution is a process in which simple life forms change into complex life forms by gradual changes. But, there is a difference between chemical and organic evolution. Differentiate by giving three points.

Ans: The formation of organic molecules from inorganic molecules is known as chemical evolution. Around four billion years ago, earth’s atmosphere consisted of chemicals such as water vapour, methane, ammonia, hydrogen,  Sunlight, heat from volcanoes and lightning caused these molecules to combine in the shallow seas and produce various organic molecules such as sugars. Slowly, these organic molecules combined to form big molecules which include proteins and simple RNA and DNA molecules.
The enzymes, proteins, RNA and DNA once formed constituted a self-replicating system enclosed in a selectively
Permeable, protective lipid sphere which further evolved into membrane bound proto cells and finally into living
Cells. This is known as organic evolution. It includes the changes from the simplest unicellular forms of life to the most complex multicellular forms.

Q. There are a number of ways by which the genes enter a population. Explain briefly the three ways

Ans: Gene flow refers to the transfer of alleles from one population to another as a result of interbreeding between members of two populations.
Mutation: are the sudden changes that take place in the DNA sequence of an organism.
Migration: Migration will change gene frequencies by bringing in more copies of an allele already in the population or by bringing in a new allele that has arisen by mutation.  

Q. why more complex organisms cannot give rise to new individuals through regeneration? 
Ans:   Complex organisms have highly differentiated tissues and organs. In this case regeneration of complex individual organism is difficult from a small piece. 

Q.Why are the small number of surviving tigers a cause of worry from the point of view of genetics?

Ans: Decrease in population; decreases the chances of recombination and variation which impacts the gene pool. As a result, there is a loss of genes. Thus they become extinct

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