Biology · Principles of Inheritance and Variation · NEET
It means genes and chromosomes do the SAME things during meiosis. Both occur in pairs. Both pairs separate so that only one member goes into each gamete. Both are then restored to pairs at fertilisation. Sutton and Boveri saw that a gene's behaviour matched a chromosome's behaviour step for step. The simple reason is that genes are physically located ON chromosomes, so a gene has no choice but to move wherever its chromosome moves.
A diploid body cell (2n) has two copies of each chromosome, called homologous chromosomes. One copy came from the father and one from the mother. Because a gene sits at a fixed spot (locus) on a chromosome, that gene also has two copies, one on each homologous chromosome. These two copies are the two alleles of the gene. So chromosomes in pairs automatically means genes (alleles) in pairs.
During meiosis, the two homologous chromosomes pair up and then separate (in anaphase I) so each gamete gets only one chromosome of the pair. Since the two alleles of a gene sit on these two homologous chromosomes, the alleles are also separated into different gametes. That is exactly Mendel's Law of Segregation, also called purity of gametes: each gamete carries only one allele of a gene.
When two gene pairs are on two DIFFERENT chromosome pairs, each chromosome pair lines up at the metaphase plate on its own. Which way one pair faces does not decide which way the other faces. So the alleles of one gene sort into gametes independently of the alleles of the other gene. This matches Mendel's Law of Independent Assortment. Note: this only works for genes on different chromosomes.
No. Mendel's laws describe the PATTERN of inheritance (factors segregate, assort independently) but Mendel never knew where the factors were. The Chromosomal Theory of Inheritance says WHERE: the factors (genes) sit on chromosomes, and it explains Mendel's laws using chromosome movement in meiosis. So the Chromosomal Theory gives the physical basis for the rules Mendel already discovered.
Walter Sutton and Theodore Boveri PROPOSED the Chromosomal Theory of Inheritance around 1902 by noticing the parallel behaviour. Thomas Hunt Morgan did the EXPERIMENTAL VERIFICATION using the fruit fly Drosophila melanogaster. Trick to remember: Sutton and Boveri = idea, Morgan = experiment/proof. NEET has directly asked both, so keep the two roles separate.
Experimental verification of the chromosomal theory of inheritance was done by
Assertion (A): Mendel's law of Independent assortment does not hold good for the genes that are located closely on the same chromosome. Reason (R): Closely located genes assort independently.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Meiosis is where homologous chromosomes pair and then separate into different gametes. That separation is what matches the segregation and independent assortment of Mendel's factors. Mitosis just copies chromosomes equally into two identical cells, so it cannot explain how alleles split into gametes.
They sit on two homologous chromosomes, one allele on each. They are at the same locus (position) on each of the two homologous chromosomes. These two chromosomes separate in meiosis, which separates the two alleles.
It fully explains independent assortment only for genes on different chromosomes. Genes that lie close together on the same chromosome are linked and tend to be inherited together, so they do not assort independently. This exception led to the study of linkage and recombination.
Yes. NEET has directly asked who proposed and who verified the chromosomal theory, and has tested the link between chromosome behaviour and Mendel's laws. It is a short but high-yield concept, so memorise the names and the meiosis link.
