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The correct answer is 1: 1.
Key Points
- 'Pure' plants refer to the homozygous condition in plants and 'hybrid' refers to the heterozygous plants.
- Homozygous - It is the condition in which the pair of alleles determining a phenotype is identical, either both dominant (TT) or both recessive (tt).
- Heterozygous - It is the condition where 2 different types of alleles are present, one dominant and one recessive (Tt).
- When a pure tall plant (TT) is crossed with a pure short plant (tt), the F1 generation produces heterozygous tall (Tt) plants.
- Upon selfing the F1 generation, that is, crossing two heterozygous tall plants, the following numbers of the F2 generation are obtained phenotypically:
- Three tall plants and one short plant
- Whereas, genotypically, the following ratio is obtained:
- One pure tall plant, two heterozygous tall plants, and one pure short plant.
- Therefore, considering the genotype, the ratio of pure tall plants to pure short plants in the F2 generation is 1:1. Hence, Option 1 is correct.
Mistake Points
- Please note here that the question asks about the ratio of "pure" tall plants to short plants in F2 generation.
- The usual ratio of 3:1 is for "all" tall plants to short plants.
- Pure Tall plants : Hybrid Tall plants : Short/Dwarf plants = TT : Tt : tt = 1:2:1
- Therefore, Pure tall : Pure short = 1:1
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Text Solution
`375,125``250,250``475,25``350,150`
Answer : A
Solution : The crossing between two heterozygous plants is as follows <br> <img src="//d10lpgp6xz60nq.cloudfront.net/physics_images/NCERT_FING_BIO_OBJ_XII_PIV_C05_E01_012_S01.png" width="80%"> <br> So, if plants obtained were 500, then the respective number of tall and dwarf plants will be 375 tall and 125 dwarf.