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I.9 Mendelism

Experiments performed by Gregor Johann Mendel on genetics and description of mechanisms of hereditery processes and formulation of principles are known as Mendelism.

Mendel studied 7 characters or 7 pairs of contrasting traits.

S.No. Character (Chromosomal position)
1 Length of plant
2 Colour of flower
3 Pod or flower position
4 Shape of pod
5 Colour of pod
6 Shape of seed
7 Colour of cotyledon
Characters Dominant Recessive
1. Stem height Tall Dwarf
2. Flower color Purple White
3. Flower position Axial Terminal
4. Pod shape Inflated Constricted
5. Pod colour Green Yellow
6. Seed shape Round Wrinkled
7. Seed colour Yellow Green

Monohybrid cross – When we consider the inheritance of one character at a time by a cross is called monohybrid cross.

Conclusions of Monohybrid Cross

Ist Conclusion : According to Mendel each genetic character is controlled by a pair of unit factor. It is known as conclusion of paired factor or unit factor.

IInd Conclusion : This conclusion is based on F1 – generation. When two different unit factors are present in single individual, then only one unit factor is able to express itself and known as dominant unit factor. Another unit factor fails to express is the recessive factor. In the presence of dominant unit factor recessive unit factor can not express and it is known as conclusion of dominance.

IIIrd Conclusion : During gamete formation; the unit factors of a pair segregate randomly and transfer inside different gamete. Each gamete receives only one factor of a pair; so gametes are pure for a particular trait. It is known as conclusion of purity of gametes or segregation.

Dihybrid cross– A cross in which study of inheritance of two pairs of contrasting traits or two characters.

Conclusion : -different type of characters present in plants assorted independently during inheritace. This is known as Conclusion of Independent Assortment. It is based on F2 – generation of dihybrid cross. The nonhomologous chromosome show random distribution during anaphase-I of meiosis.

ie The F2 generation plant produce two new phenotypes, so inheritance of seed coat colour is independent from the inheritance of shape of seed. Otherwise It can not possible to obtain yellow wrinkled and green round type of seeds.

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