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Q.
If F1 generation has all tall progenies and ratio of F2 generation is 3 : 1 (tall: dwarf), then it proves
Odisha JEEOdisha JEE 2011Principles of Inheritance and Variation
Solution:
In $F_1$ the dominant phenotype appears, the recessive phenotype is not lost but reappears in $F_2$. This suggest that there is not blending of Mendelian factors in $F_1$, but they stay together and only one is expressed. At the time of the formation of gametes, these two factors obviously separate or segregate, otherwise recessive type will not appear in $F_2$. The gametes which are formed are always pure for a particular character. A gamete may carry either the dominant or the recessive factors but not both as we find in $F_1$ individuals. This is why it is called either as ‘principle of segregation’ or as ‘law of purity of gametes’. This concept of segregation is often called Mendel’s first principle. While a 3 : 1 ratio in $F_2$ generation of a monohybrid cross suggest that segregation of alleles does take place which can be confirmed by test cross.