1. The branch of biological science of inheritance which deals with the study of heredity and variation is called genetics. Gregor Johann Mendel is considered as father of genetics because the first scientific study of genetics was carried by him and introduced the concept of genes as the basic unit of heredity.

  2. Heredity is the phenomenon by which Living organisms transmit parental characteristics to their off springs.
    Heredity characteristics are the characteristics of the parents which are transmitted to their off springs.
     Any too examples are:
            - Type of hair in Human beings.
            - Color of the eyes.

  3. The tiny units of heredity located in the chromosomes is called genes.
    The concept of 'gene' was introduced by sulten and the term 'gene' was introduced by Johannsom. It is located in chrosomes and arranged in linear fashion. It determine the physical, anatomical and physiological characteristics of organism. These characteristics are transmitted from one generation to other.

  4. Allelomorph is one of a gene or pair of matching genes. It contains a pair of identical alleles.

  5. When the both alleles of a particular gene are identical, it is called homozygous.

  6. When two alleles of a particular gene are not identical, it is called heterozygous.

  7. The organism produced after cross fertilization between two genetically different organisms is called hybrids.
    Hybrids are produced by crossing between organisms having two contrasting characteristics. This process is called hybridization.

  8. Mendel selected pea plant for his study because of following reasons:
            - Pea plant can be cultivated easily and have a short life cycle.
            - Breeding controlled easily.
            - Pea plant produce large number of off springs after fertilization.
            - The flower of pea plants are adequate in size and easy to handle.
            - Pea plant are found in various species.

  9. a.    Genotype and Phenotype.

    The internal genetic makeup or appearance of an organism is called genotype.
    The external appearance of an organism for a contrasting characteristic is called phenotype.
    Parental characteristics can be found in genotype.Parental characteristics cannot be found 100% in phenotype.
    It is expressed in letters.It is expressed in words.

    b.    Dominant characteristics and Recessive characteristics.

    Dominant characteristics
    Recessive characteristics
    The characteristics which are prominent and appear in successive generations are called dominant characteristics.The suppressed characteristics which cannot be expressed in successive generations are called recessive characteristics.
    Dominant characteristics are seen over recessive.Recessive characteristics remains hidden.

    c.    F1 generations and F2 generations.

    F1 generations
    F2 generations
    The generation obtained by crossing two parental stocks is called F1 generations.The generation obtained by crossing two parental stocks of F1 generations is F2 generations.
    The parents of F1 generation have pure genotype.The parents of F2 generation does not have pure genotype.
    It is also first filial generation.It is also second filial generation.

    d.    Monohybrid cross and Dihybrid cross.

    Monohybrid cross
    Dihybrid cross
    The cross involving only one pair of constracting characteristics is called monohybrid cross.The cross involving two pair of constracting characteristics is called Dihybrid cross.
    Here, off springs having phenotypic ratio of 3:1 are produced in F2 generation.Here, off springs having phenotypic ratio of 9:3:3:1 are produced in F2 generation.

  10. Mendel's law of dominance states that, "In a crossing between pure organism for constrasting characteristics of a pair, only one characteristics of a pair appears in the first filial generation.
    Let us consider a pure tall pea plants (TT) and a pure dwarf pea plant (tt). When a pure tall pea plant is cross pollinated with the pure dwarf one, all the off springs will be tall in first filial generation. Here, tallness appears by suppressing the dwarfness. In this cross, tall is the dominant characteristics as it appears in F1 generation and dwarf is the recessive characteristics as it remains hidden.

  11. Law of segregation states that, "The hybrid obtained in F1 generation contains two contrasting characteristics of dominant and ressive in nature. Those characteristics remain together for long time in hybrids but don't mix with each other and separates at the time of gametes gets only a pure characteristics."
    The monohybrid cross between a pure red flowered pea plant and pure white flowered pea plant up to the 2nd filial generation. In F1 generation all pea plants produced hybrid red (Rr) with dominant and recessive characters R and r respectively. Both character remains together for long time without mixing and finally separates into two different pure gametes. These hybrid after breeding, produces 3 types of off springs, i.e pure red, hybrid red & pure white in the ratio of 1:2:1 in 2nd filial generations.

  12. Dihybrid cross is the cross in which to pairs of constracting characteristics are taken into consideration.
    For example:    Cross between red-flowered tall pea plant and white flowered dwarf pea plant.

  13. Yes, Mendel's law applies the human beings also.
    Any two difficulties that Mendel would have faced if he had carried his experiments on human beings instead of pea plants are:
            - Human beings have long term life cycle. It is impossible to observe many generations.
            - It is impossible to cross between siblings.
            - Human being have many contrasting characters which makes difficult to study them.
            - It is easier to handle pea plant than human as fertilization and reproduction process is easier and short-term in pea plant.

  14. The difference between mutation and variation are:

    A sudden heritable change in the genetic material of an organism is called mutation.
    The structural difference that provides individuality to each member of a species is called variation.
    Various factors like uv rays, x-rays, etc. are responsible for mutation.
    Structural and functional difference of gene, environment factors are responsible for variation.
    It is rarely seen due to genetical disorder.
    It I usually seen in every species.

  15. a.    Which filial generation does this result belongs to?
            - This result belongs to 2nd filial generation.
    b.    What is the percentage of pea plant having hybrid characteristics?
            - 50 percentage of pea plant have hybrid characteristics.
    c.    Which pair of genes indicate pure tall plant?
            - (IT) indicates pure tall pea plant.

  16. Here,

            Bb is a black mice because B is dominant character and bb is a pure white mice.
                    Total black mice (Bb) = 2
                    And total white mice (bb) = 2
                    So,    phenotype ratio = 2 : 2
                                                          = 1 : 1

  17. The significance of Mendelism are
            - Diseases resistant and high yielding varieties of plants and animals can be produced by application of Mendelism.
            - Hybrids with desired characteristics can be produced.
            - The genotypes and phenotypes likely to be produced in successive generations can be predicted before the cross is made.
            - Dominant and recessive characteristics of organism can be known.

  18. The structural differences that provide individuality to each member of a species is called variation. 
    The factors that bring out genetic variation are:
            - Structural and functional differences of a gene.
            - Environmental factors like food, light, temperature, etc.

  19. a.    Write down the genotype and phenotype of mother.
            - Genotype: bb
            - Phenotype: Pure white
    b.    What is the phenotypic and genotype ratio of black and white complexion in F2generation.
            - Phenotype: 2:2 or 1:1
            - Genotype: 2:2 or 1:1

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