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# In a homozygous pea plant, axial flowers (A) are dominant over terminal flowers (a). What is the phenotypic and genotypic ratio in the above cross shown in (ii)?

Last updated date: 24th Jun 2024
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Hint: Gregor Mendel conducted hybridization on pea plants. For the first time in biology, he used some mathematical logic to explain the pattern of inheritance. He used several true-breeding pea lines. Mendel selected 14 true-breeding pea plant varieties, as pairs which were similar except for one character with contrasting traits.

Complete step by step answer: In the pea plant, “AA” will be the pair of an allele for the dominant gene which is of axial flowers whereas; the “aa” allele will be of the terminal flowers. “AA” and “aa” are called the genotype of the plant while the elaborated terms axial and terminal are the phenotype. The cross will be made as given below:

 Gametes Terminal flowersa Terminal flowersa Axial flowersA Aa Aa Axial flowersA Aa Aa

 Gametes Terminal flowersa Terminal flowersa Axial flowersA Aa Aa Axial flowersA Aa Aa

Phenotypic ratio: axial: terminal
3: 1
Genotypic ratio:AA : Aa : aa
1: 2: 1
This concludes that, at F2, three-fourth of the flowers is axial and one-fourth of them are terminal.

Additional information: Contrasting traits studied by Mendel in pea are:

 Serial number Characters Contrasting traits Chromosome number 1. Stem height Tall/dwarf 4 2. Flower colour Violet/white 1 3. Flower position Axial/terminal 4 4. Pod shape Inflated/constricted 4 5. Pod colour Green/yellow 5 6. Seed Shape Round/wrinkled 7 7. Seed colour Yellow/green 1

Note: When there is an inheritance of a single contrasting trait at a time by two parents, it is referred to as monohybrid ratio. When there is a monohybrid cross between two pure breeding varieties all dominant traits are obtained in the F1 generation, in F2 generation upon selfing it gives the monohybrid phenotypic ratio of 3:1 and a genotypic ratio of 1:2:1 which is 1 homozygous dominant: 2 heterozygous dominant: 1 homozygous recessive.