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    Heredity and Evolution
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    How is the sex of the child determined in human beings?

    In human, 23 pairs (46) chromosomes are present out of these 22 pairs have a maternal and a paternal copy. These chromosomes (autosomes) determine the characters other than sex. The 23rd pair of chromosomes called sex chromosomes. Women have perfect pair of sex chromosomes, both called XX chromosomes. Men have a mismatched pair of chromosomes—one is a normal size X chromosome and a short one called Y chromosome. So, women have XX chromosomes and men have XY sex chromosomes.
    All children will inherit an X chromosome from their mother regardless of whether they are boys or girls. It means that the sex of the children will be determined by what sex chromosome they inherit from their father. A child who inherits an X chromosome from father will be girl, and one who inherits a Y chromosome from father will be a boy.
    In human, 23 pairs (46) chromosomes are present out of these 22 pairs
    Fig. Birth of a girl or boy baby

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    What factors could lead to the rise of a new species?
    Factors that could lead to the rise of a new species are:
    i. Accumulated variations favourable to the changing natural environment.
    ii. Geographical isolation of a population.
    iii. Natural selection.
    iv. Action of different environmental factors on these isolated populations.
    v. Reproductive isolation and change of number of chromosomes.
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    Why are traits acquired during the life-time of an individual not inherited?
    The traits acquired during the life-time are changes in the non–reproductive cells of the organism and cannot be passed on to the DNA of the germ
    cells. Thus the aquired traits cannot be inherited by the next generations.

     

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    Why are the small numbers of surviving tigers a cause of worry from the point of view of genetics?
    The smaller number of tigers means lesser variations which in turn means lesser ability to adapt to the changing environment. For example, if a deadly disease infects the tigers, all the tigers may die from it as there would be less variation in the genotype to survive the disease. Decrease in population of tigers also indicates that tiger variants are not adapted to the existing environment and may become extinct soon.
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    What are the different ways in which individuals with a particular trait may increase in a population?

    The individuals with a particular trait may increase in the population due to suitable variations and natural selection. If a variation occurs in a population and that variation results in better adaptation of the organism to the prevailing conditions, then the trait would be selected naturally and more individuals with that trait would survive in the population.
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