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Grade: 12
        
how to determine the character/trait present on the 7th chromosome of a pea plant?
3 years ago

Answers : (1)

Raheema Javed
askIITians Faculty
156 Points
							Mendel’s Experiments on Sweet Pea

Selection of the material :Mendel selected garden sweet pea(Pisum sativum)for his hybridization experiments for of the following reasons : (i) Plants are annual and easy to cultivate. (ii) Peas have many distinct, well-defined and easily observable morphological characteristics (traits). (iii) Flowers are bisexual and naturally self-fertilizing, but they can also be easily cross-fertilized. (iv) The offspring of cross-fertilized plants are fertile. (v) Flowers are sufficiently large for easy emasculation (removal of stamens) and artificial cross-pollination.

Selection of characters (traits) :Mendel selected 14 different varieties of the pea and grouped them into seven pairs. Each pair was considered for a specifictrait(characteristic) such as flower color or seed shape or stem length, etc. The two members of each pair showed contrasting forms of the chosen trait, ,e.g., in a pair selected for stem length, one variety had a tall stem (6-7 feet tall) while the other had adwarfstem

Nature and procedure of the experiments :Mendel had very clear concepts of what he was doing and what requirements were necessary if he had to arrive at the conclusions accurately and successfully. He realized the necessity of: (i) using pure breeding parent plants; (ii) considering only one character at a time during the breeding experiments; (iii) always keeping the generations separate; (iv) and using statistical and mathematical principles to compute the obtained results properly.

Mendel conducted his experiments in three stages.

Stage-1 :
It involved selecting a pair of parents with contrasting characters and obtaining each parent plant in pure condition ,i.e,. breeding true for the characters selected.
For example, Mendel ensured that the plant selected for round seeds produced only round seeds on self-fertilization and the plant selected for wrinkled seeds produced only wrinkled seeds . Such pure, true-breeding parents were obtained by Mendel through repeated self fertilizing, generation after generation.

Stage -2 :It involved crossing of the selected parents. Of the pair, one plant was used as the male parent and the other as the female parent. Pollen from the male was dusted on the stigma of the female parent for cross-pollination. Mendel conductedreciprocal crossesalso.
For example :in one cross, the round seeded variety was used as the male parent and the wrinkled seeded variety as the female parent, while in the reciprocal cross of the same parents, the wrinkled variety was used as the male parent and the round seeded variety as the female parent. This may be represented as follows :Male Parent Female Parent Cross - I Rounded seeded Wrinkled seeded Reciprocal Cross Wrinkledd seeded Rounded seeded

Stage - 3 :In the third stage, Mendel allowed each F1hybrid to self-pollinate and produce the next, i.e.,Second Filialgeneration or F2generation.

Mendel conducted a similar type of hybridization experiment separately for each of the seven pairs. He meticulously maintained a complete record of the actual number of each type of offspring in every generation (i.e., data of qualitative as well as quantitative results).

Mendel observed that in each of these crosses, all the F1hybrids resembled only one parent, while the character of the other parent was not seen in the F1hybrid. For example, in a cross between round X wrinkled type, the F1were all round seeds only. The wrinkled character was not seen. The character which appears in the F1hybrid was termeddominantand the other asrecessiveby Mendel. Thus, in each of the seven pairs, one form is dominant and the other is recessive (See Table 1.1). The F2progeny showed presence of both parental forms which always appeared in the ratio of 3 dominants : 1 recessive. This 3:1F2ratiowas termed as themonohybrid ratio.

3 years ago
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