(a) Define ‘natural selection’.
(b) “Only variations that confer an advantage to an individual organism will survive in a population”. Do you agree with this statement ? Give reason for your answer.
(a) Natural selection is the process of evolution of a species whereby characteristics which help individual organisms to survive and reproduce are passed on to their offspring, and those characteristics which do not help are not passed on.
(b) Yes, only those variations that confer advantage to an individual organism will survive in a population. This will become clear from the following example. Suppose there is a population of red beetles in the green bushes and a colour variation arises during reproduction so that one beetle is now green in colour (instead of red). This variation offers advantage of survival because the green beetle can mix up with green bushes, it cannot be spotted and eaten up by a crow and hence its population will increase. If, however, the variation had produced a blue coloured beetle, then this colour could not offer any survival advantage because blue beetle in green bushes could be easily spotted by a crow and eaten by it.
(a) If a normal human cell has 46 chromosomes, how many chromosomes will be there in a human (;) sperm cell, and (ii) zygote ?
(b) What sizes of plants are produced if both parents have genes Tt ?
How are fossils formed? Describe, in brief, two methods of determining the age of fossils. [All India]
a) Name the scientist who gave the theory of origin of life on earth. What is this theory ?
(b) How are those species which are now ‘extinct’ studied ?
Will geographical isolation be a major factor in the speciation of an organism that reproduces asexually ? Why or why not ?
Define variation in relation to a species. Why is variation beneficial to the species? [Delhi]
If the 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 ?
(a) What is the genotype of dwarf plants which always produced dwarf offspring ?
(b) What is the genotype of tall plants which always produced tall offspring ?
(c) What is the genotype of
Does genetic combination of mother play a significant role in determining the sex of a new born baby ?
Name the various tools of tracing evolutionary relationships which have been used for studying human evolution.
A woman has only daughters. Analyse the situation genetically and provide a suitable explanation.
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 ?
What do you understand by the double helical structure of DNA? Who proposed this structure?
How is the equal genetic contribution of male and female parents ensured in the progeny? [Delhi]
Give an example of body characteristics used to determine how close two species are in terms of evolution and explain it. [All India]
What is meant by the term speciation? List four factors which could lead to speciation. [Delhi]
State whether the following statement is true or false :
The sex of an infant is not a case of inheritance of characteristics.
The gene for red hair is recessive to the gene for black hair. What will be the hair colour of a person if he inherits a gene for red hair from his mother and a gene for black hair from his father ?
Give the contrasting traits of the following characters in pea plant and mention which is dominant and which is recessive :
(a) Yellow seed (b) Round seed
(a) Why did Mendel choose pea plants for conducting his experiments on inheritance ?
(b) State Mendel’s second law of inheritance.
State one characteristic which shows that the birds are very closely related to dinosaurs.
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 ?
Why are the small numbers of surviving tigers a cause of worry from the point of view of genetics ?
Will geographical isolation be a major factor in the speciation of an organism that reproduces asexually ? Give reason for your answer.
Out of bacteria, spider, fish and chimpanzee, which organism has a better body design in evolutionary terms ? Give reason for your answer.
(a) Define ‘speciation’. Explain how speciation occurs.
(b) Will geographical isolation be a major factor in the speciation of a self-pollinating plant species ? Give reason for your answer.
Does the occurrence of diversity of animals on earth suggest their diverse ancestry also? Discuss this point in the light of evolution.
A man with blood group A marries a woman with blood 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 ?
Give an example of characteristics being used to determine how close two species am in evolutionary terms ?
In evolutionary terms, can we say which among bacteria, spiders, fish and chimpanzees have a ‘better body design’ why or why not ?
