Biology · Principles of Inheritance and Variation · NEET
TT is a genotype. It shows the two alleles inside the cell (both dominant T). The matching phenotype is 'tall' — the trait you can see. Rule: letters like TT, Tt, tt are always genotypes; words like tall, dwarf, red, white are phenotypes.
Yes, and this is the key NEET idea. A tall pea plant can be TT (homozygous) or Tt (heterozygous). Both look exactly the same (tall phenotype) because T is dominant and hides the recessive t. So the same phenotype can come from two different genotypes. NCERT says by just looking at a dominant trait, you cannot know the genotype.
In a Tt x Tt cross, the F2 genotypes are 1 TT : 2 Tt : 1 tt (that is the genotypic ratio 1:2:1). But TT and Tt both look tall, so we see 3 tall : 1 dwarf (the phenotypic ratio 3:1). The genotype counts the gene combinations; the phenotype counts only the visible traits. The 3 tall = 1 TT + 2 Tt.
For a recessive trait, yes. A dwarf plant is always tt — there is no hidden option — so its phenotype tells you its genotype exactly. That is why Mendel used a test cross with the recessive parent to find out whether a tall plant was TT or Tt.
The environment can change the phenotype but not the genotype. Genotype is fixed by the alleles you inherit. Phenotype is how those genes actually show up, and things like food, light or temperature can affect the final visible trait. This is why phenotype = genotype + environment.
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
The genotypes of a Husband and Wife are IAIB and IAi. Among the blood types of their children, how many different genotypes and phenotypes are possible?
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Genotype is the set of alleles (genes) an organism has, written as letters like TT or Tt. Phenotype is the visible or measurable trait produced by those genes, like tall, dwarf or red flower.
Blood group A, B, AB or O is a phenotype (what you observe). The genotype is the allele pair behind it, such as IAIA or IAi for blood group A. Different genotypes can give the same blood-group phenotype.
Dominant alleles hide recessive ones. So a dominant trait (like tall) can come from TT or Tt, and both look the same from outside. We use a test cross (crossing with the recessive parent) to reveal the hidden genotype.
Only the phenotype. Genotype is fixed at fertilisation. The final phenotype depends on genotype plus environment, so factors like nutrition or temperature can change how a trait looks.
Usually yes for a fixed environment, but the phenotype can vary if the environment changes. The genotype sets the possible outcome, and the environment can shift the final visible trait.
