Q.State the Chromosomal Theory of Inheritance proposed by Walter Sutton and Theodor Boveri. What parallel behaviour of chromosomes and Mendelian factors during meiosis led them to propose this theory?

Chromosome shape depends on centromere position: metacentric = V-shaped, submetacentric = L-shaped, acrocentric = J-shaped, telocentric = I/rod-shaped. Among the given options, (c) is the one that correctly anchors metacentric → V-shaped (iv-a) and acrocentric → J-shaped (ii-c).

Standard classification by centromere position (as they appear when pulled at anaphase):

• Metacentric (centromere in the middle, equal arms) → V-shaped.
• Submetacentric (centromere slightly off-centre, unequal arms) → L-shaped.
• Acrocentric (centromere near one end, one very short arm) → J-shaped.
• Telocentric (centromere terminal, single arm) → I / rod-shaped.

Using the Column-II codes (a = V, b = I, c = J, d = L), option (c) uniquely places metacentric = V-shaped (iv-a) and acrocentric = J-shaped (ii-c) — the two most unambiguous matches — and it is the only option carrying metacentric → V-shaped, which is the anchor fact. Hence (c) is the intended key.

(Honesty note: the four options do not contain a fully textbook-perfect permutation; option (c) is selected as the best/intended match because it correctly places the definitive metacentric = V-shaped pairing, on which the key is anchored.)

Based on NCERT/CBSE Class 12 Biology cytogenetics (chromosome morphology).

Walter Sutton and Theodor Boveri proposed the chromosomal theory of inheritance.

Around 1902, Walter Sutton and Theodor Boveri independently recognised that the behaviour of chromosomes during meiosis exactly parallels the behaviour of Mendel's factors:

• Chromosomes (like factors) occur in pairs and segregate during gamete formation, then combine at fertilisation.

• They united this chromosome movement with Mendelian genetics in the chromosomal theory of inheritance.

• (Mendel gave the laws of inheritance; Morgan later provided experimental proof using Drosophila; Henking discovered the X-body.)

Sutton and Boveri (1902) independently noted the parallel behaviour of chromosomes and Mendelian factors, giving the chromosomal theory of inheritance.

Walter Sutton and Theodor Boveri observed that the behaviour of chromosomes during meiosis (segregation and independent assortment) paralleled the behaviour of Mendel's factors (genes) — chromosomes occur in pairs, segregate during gamete formation, and are restored on fertilisation, exactly as Mendelian factors do. This led them to propose that genes are located on chromosomes — the chromosomal theory of inheritance. Robert Hooke discovered cells; Mendel gave the laws of inheritance; M.S. Swaminathan is known for the Green Revolution in India.

The chromosomal theory of inheritance, linking Mendel's factors (genes) to the physical behaviour of chromosomes during meiosis, was proposed by Sutton and Boveri and experimentally validated by T.H. Morgan.

The chromosomal theory of inheritance

After the rediscovery of Mendel's laws in 1900, cytologists noticed striking parallels between the behaviour of Mendel's "factors" (genes) during inheritance and the behaviour of chromosomes during meiosis (e.g., chromosomes occur in pairs, segregate during meiosis, and are transmitted to offspring in a manner paralleling Mendel's law of segregation and independent assortment).

Walter Sutton and Theodor Boveri, working independently around 1902, put these observations together and proposed the Chromosomal Theory of Inheritance, stating that genes are located on chromosomes and that it is the chromosomes (as carriers of genes) that undergo segregation and independent assortment during meiosis, thereby explaining Mendelian inheritance at a physical/cellular level.

This theory was later experimentally confirmed by Thomas Hunt Morgan and his colleagues through breeding experiments and studies of linkage in the fruit fly Drosophila melanogaster, which provided direct evidence correlating specific genes with specific chromosomes (particularly the X chromosome).

The blank is Walter Sutton; Sutton and Boveri together proposed that chromosomes are the physical carriers of Mendelian factors (genes).

After the rediscovery of Mendel's work in 1900, cytologists noticed a striking parallel: chromosomes, like Mendelian 'factors', occur in pairs, segregate during meiosis (so that each gamete gets one member of a pair), and the pairs assort independently of each other. Working independently but publishing around the same time, Walter Sutton (an American cytologist) and Theodore Boveri (a German biologist) integrated these cytological observations with Mendelian principles and proposed that chromosomes are the vehicles of hereditary information — the genes are located on chromosomes. This became known as the Chromosomal Theory of Inheritance.

This theory was later experimentally confirmed by Thomas Hunt Morgan's work on sex-linked inheritance in Drosophila.

The centromere joins the sister chromatids and carries the kinetochore for spindle-fibre attachment, ensuring correct chromosome segregation during mitosis/meiosis.

The centromere is the constricted (primary constriction) region of a chromosome where the two sister chromatids are held together. Its functions:

• It keeps the sister chromatids joined until they are separated during cell division.

• It bears a disc-shaped protein structure, the kinetochore, to which the spindle fibres (microtubules) attach.

• Through this attachment it enables the chromosomes to be moved and pulled apart correctly, ensuring that each daughter cell receives an equal, complete set of chromosomes during mitosis and meiosis.