MENDAL'S EXPERIMENT

Mendel's conclusion about inheritence of characters were based on his hybridization  experiments  in which  he considered  either one pair of contrasting  characters  involving  cross between plants with these characters .The  cross involving only one pair of  contrasting  characters is called monohybridization  and the related experiment is callen monohybrid experiment  or monohybrid cross .Likewise ,the cross involving two pairs of contrasting characters  is called dihybridization  and the related experiment is refered to as dihybrid experiment or cross .          Mendel's series of experiment  involved  seven pairs of contrasting characters  of the edible garden pea , pisum sativum namely ,smooth and wrinkled seed ,yellow and green peas , tall and short stems,axial or terminal flowers ,white or grey seed-coats ,yellow or green cotyledons ,etc peas are normally self -pollinating but mendel tried the experiment of transferring the pollen of one variety of pea to the stigma  of the other .        MONO HYBRID EXPERIMENT ;Mendel first cross pea-plants differing  in a single pair  of contrasting characters ,such as tallnesss or shortness of plants .Thereafter ,the seeds obtain from these plants i.e., the parental plants [p] were sown to obtain plants from the fist felial  generation ,indicated by f1 in abbreviated form .The flower of the f1 generation were allowed to second generation ,indicated by f1 in abbreviated  form. The flowers of the f1generation were allowed to self pollinate.All  the resultant seeds were collected  and sown to give the second filial or f2 generation .In this ,mendal found tall plants  and short plants in the proportional  of 3 tall to 1 short -finally all the plants of the f2 generation  and from the resultant weeds an f3 generation was obtained .Seed from the short plants of the f2 generation gave rise to nothing but  short plants  in the f2 generation .But the tall of f2 didnot all behave in the same  way .One third  of them gave rise  to nothing  but talls in thef3 , but  the other two thirds  segre gated like the plants of the f1 generation, giving rise to the short and tall plants  in the proportion of 3to 1 .                                                                                                 As a result of his experiments  mendal was able to state certain principles or laws  which now form the basis for all studies  of heredity or genetics [1] Law of Paired Units ; There are unit carriers  of heredity which occurs in pairs .One of each  pair come from the mother while  the other came from the father  . The unit carriers were caslled by mendel determiners  or factors but now they are known as genes . [2] Law Of Dominance ; when two hereditary units of pair are unlike ,the one which functions and produces  its character or effect is called dominant while the others whch remains undeveloped or unexpressed is called recessive .If a plant has one dominant and one recessive  gene , it exhibits the dominant  trait .[3] Law Of Segregation ; That is , the unit character or the gene  keep thier identity and in each generation they are free to seperate from each other and to be redistributed in the offspring .                                                                                     In the above  experiment  when two  of the tall plants obtain from cross of  a tall  and short peas were crossed , some  of the resulting pea plants [f2]  were tall and other short . This  led mendal to the concept of segregation .Thus the tall plants of f1 generation  have genes or factors for  both tallness or shortness .When these f1 plants  plants are crossed some of the offspring  recieve a gene for tallness  from each parent ,others recieve one gene for tallness  and other for shortness ,while  athird group of plants  get two genes for shortness