Biology · Principles of Inheritance and Variation · NEET
No. A gene is the whole unit that controls a trait, like the gene for stem height in pea. An allele is only one form of that gene. The height gene has two alleles: T for tall and t for dwarf. So one gene can have two or more alleles. In NCERT, alleles are defined as the two or more alternative forms of a gene.
A locus is the position, not the gene. It is the fixed spot on a chromosome where a gene is located. Think of it as an address. The gene lives at that address, and whichever allele you have (T or t) sits at the same locus. The plural of locus is loci.
They are two alleles of the same gene. Both control the same trait (plant height) and both sit at the same locus on the same chromosome. Capital T is the dominant allele and small t is the recessive allele. They are never called two different genes because they control the same character.
Yes. In a single individual only two alleles are present (one on each homologous chromosome). But in a population a gene can have many forms, called multiple alleles. The best NEET example is the ABO blood group gene I, which has three alleles: IA, IB and i. Still, any one person carries only two of them.
On homologous chromosomes. A diploid organism has chromosomes in pairs. One allele is on the chromosome from the father and the matching allele is on the chromosome from the mother, both at the same locus. That is why we write genotypes as pairs like TT, Tt or tt.
Those words describe the pair of alleles at a locus. If both alleles are the same (TT or tt) the organism is homozygous. If the two alleles are different (Tt) it is heterozygous. So gene, allele and locus describe the parts, while homozygous and heterozygous describe the combination you have.
Match List I with List II. List I: A. Two or more alternative forms of a gene; B. Cross of F1 progeny with homozygous recessive parent; C. Cross of F1 progeny with any of the parents; D. Number of chromosome sets in plant. List II: I. Back cross; II. Ploidy; III. Allele; IV. Test cross.
Identify the wrong statement with reference to the gene 'I' that controls ABO blood groups.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
A gene is the DNA unit that controls a trait. An allele is one version of that gene, such as T or t. A locus is the exact spot on the chromosome where the gene is found.
Only two, one on each homologous chromosome. A gene may have many alleles in a whole population (multiple alleles), but a single diploid individual carries just two at that locus.
Yes. Both alleles of a gene occupy the same locus, one on each chromosome of a homologous pair. That is why they control the same trait.
T is an allele, the dominant form of the plant-height gene. Its recessive partner is t. Together T and t are the two alleles of one height gene.
NEET regularly asks match-the-column and one-line-definition questions using the exact words "alternative form of a gene" (allele) and "position on chromosome" (locus). Knowing the precise word wins these marks quickly.
