Biology · Principles of Inheritance and Variation · NEET
P stands for Parental generation, the two starting plants. F stands for Filial, a word that means 'children' or 'offspring'. So F1 = first filial generation = the first set of children. F2 = second filial generation = the next set of children (the grandchildren of P). NEET loves to check if you know the letter 'F' means children, not 'father'.
You do NOT cross F1 with the parents to get F2. You get F2 by selfing the F1 plants (self-pollination) or by crossing two F1 plants with each other. Only the children of the F1 plants are called F2. This is the step where the hidden recessive trait comes back and the 3:1 ratio appears.
The tall parent is TT and the dwarf parent is tt. Every F1 plant gets one T and one t, so its genotype is Tt. Tall (T) is dominant over dwarf (t), so Tt looks tall. That is why 100% of F1 are tall and none are dwarf. The dwarf trait is hidden, not lost.
Each F1 (Tt) makes two kinds of gametes: half carry T and half carry t. When two Tt plants cross, some offspring get t from both sides and become tt (dwarf). So dwarf reappears in F2 in a 3 tall : 1 dwarf phenotype ratio. This proves the recessive factor was only hidden in F1, not destroyed.
F1 are the direct children of the pure parents and all look the same (uniform). F2 are the children of F1 and they show variation (both traits reappear, e.g. tall and dwarf in a 3:1 ratio). Uniform = F1, Variety = F2.
For Tt x Tt, the F2 genotype ratio is 1 TT : 2 Tt : 1 tt (that is 1 homozygous tall : 2 heterozygous tall : 1 dwarf). The phenotype ratio is 3 tall : 1 dwarf. NEET often asks for the genotype ratio (1:2:1), so read the question carefully.
The production of gametes by the parents, the formation of zygotes, the F1 and F2 plants, can be understood using:
A tall true breeding garden pea plant is crossed with a dwarf true breeding garden pea plant. When the F1 plants were selfed the resulting genotypes were in the ratio:
Assertion A: In an experiment, Mendel observed that the F1 progeny plants are all tall and none are dwarf. Reason R: Stem height is a contrasting trait, with tall being dominant and dwarf being recessive. Choose the most appropriate answer:
Try the real previous-year questions from this chapter — each with the answer and a full solution.
F1 means the first children (first filial generation), NOT the parents. The parents are called the P generation. F1 are the offspring produced when the two P plants are crossed.
F stands for Filial, which comes from a Latin word meaning 'son or daughter'. So F1 = first filial = first children, and F2 = second filial = next children.
No. F2 is made by selfing or crossing F1 plants with each other. A back cross is when F1 is crossed with one of its own parents. These are different things and NEET tests this difference.
The F2 phenotype ratio is 3 dominant : 1 recessive (for example 3 tall : 1 dwarf). The F2 genotype ratio is 1 : 2 : 1 (1 homozygous dominant : 2 heterozygous : 1 homozygous recessive).
We self F1 to produce the F2 generation and to check what traits are hidden. Selfing Tt x Tt lets the recessive dwarf trait reappear, which proved Mendel's idea that factors (genes) stay pure and separate during gamete formation.
