Biology · Principles of Inheritance and Variation · NEET
A dominant allele expresses its trait even in a single copy (heterozygous, like Tt). A recessive allele expresses its trait only when present in two copies (homozygous recessive, like tt). In Tt the plant is tall because T is dominant; t (dwarf) is masked and stays hidden. This masking of the recessive allele in a heterozygote is exactly what Mendel's Law of Dominance describes, and NEET asks it directly.
Only one copy. That is the whole point of being 'dominant'. If a plant is Tt (one dominant T, one recessive t), it is still tall. A recessive trait (like dwarf) needs two recessive alleles, tt, before it can appear. This is the most common confusion, and NEET loves to test it with genotypes like Tt vs tt.
Because a dominant allele usually makes a working (functional) product, while the recessive allele often makes a non-working or reduced product. In Tt, the one T allele makes enough functional product to give the full tall trait, so t contributes nothing visible. The recessive trait is not lost; it is only hidden, and it can reappear in the F2 generation when two t alleles come together.
By convention, the dominant allele is written with a CAPITAL letter (T, tall) and the recessive allele with the SAME letter in small case (t, dwarf). Both alleles use the same letter because they are two forms of the SAME gene sitting at the same locus. NEET diagrams and Punnett squares follow this rule, so remember: capital = dominant, small = recessive.
No. 'Dominant' only means the allele shows its trait even in one copy; it says nothing about how common the allele is. A dominant allele can be rare, and a recessive allele can be very common in a population. Polydactyly (extra fingers) is dominant but rare. Do not mix up 'dominant' (about masking) with 'common' (about frequency) in NEET.
Yes. A tall plant can be TT (two dominant) or Tt (one dominant, one recessive). Both LOOK tall, so they have the same phenotype but different genotypes. This is why we cannot know the exact alleles of a tall plant just by looking; we use a test cross with tt to find out. This idea directly connects to genotype vs phenotype.
Which one of the following can be explained on the basis of Mendel's law of Dominance? A. Out of one pair of factors one is dominant and the other is recessive. B. Alleles do not show any expression and both the characters appear as such in F2 generation. C. Factors occur in pairs in normal diploid plants. D. The discrete unit controlling a particular character is called factor. E. The expression of only one of the parental characters is found in a monohybrid cross.
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.
Match the following: (a) Dominance (b) Codominance (c) Pleiotropy (d) Polygenic inheritance with (i) Many genes govern a single character (ii) In a heterozygous organism only one allele expresses itself (iii) In a heterozygous organism both alleles express themselves fully (iv) A single gene influences many characters.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
An allele that shows its trait even when present in a single copy (as in the heterozygote Tt).
An allele that shows its trait only when present in two copies (homozygous recessive, tt); in a heterozygote it stays hidden.
Same letter of the gene: capital for dominant (T = tall) and small case for recessive (t = dwarf), because they are two forms of the same gene.
No. Dominant only means it masks the recessive allele in a heterozygote. It does not mean the allele is stronger, healthier, or more common.
Yes. A recessive allele can be carried hidden in heterozygotes (Tt) for a generation and reappear when two carriers pass on t, giving tt offspring in the F2 generation.
