Chromosomal Theory Inheritance
குரோமோசோம் மரபுவழி கோட்பாடு
Mendel’s factors were invisible abstractions until Sutton and Boveri mapped them to physical structures. If you cannot visualize chromosomes moving during Anaphase I, you do not understand inheritance. Stop guessing; start tracking the physical movement of DNA.
The idea
Sutton and Boveri observed that the behavior of chromosomes is parallel to the behavior of genes. Both occur in pairs in diploid organisms. During meiosis, homologous chromosomes segregate, ensuring that each gamete receives only one allele of a pair. This physical segregation of chromosomes is the mechanism that explains Mendel’s Law of Segregation.
Why it matters
It provides the physical basis for Mendel's laws by explaining that genes are located on chromosomes which segregate during meiosis.
NEET lens
NEET focuses on the parallel movement of chromosomes and genes. Memorize the table comparing them: both occur in pairs, segregate during gamete formation, and assort independently. Do not confuse Sutton-Boveri with Morgan’s Linkage experiments. Expect at least one question linking meiosis to Mendelian ratios.
Clinical significance
When chromosomal segregation fails during meiosis, it leads to non-disjunction. This results in aneuploidy, such as Down syndrome or Turner syndrome. The physical failure of chromosomes to separate correctly is the direct cause of these genetic disorders.
Introduction
The Chromosomal Theory of Inheritance (Sutton and Boveri, 1902–1904) proposes that genes are located on chromosomes and that the behaviour of chromosomes during meiosis accounts for Mendelian segregation and independent assortment.
Core concept
Historical context: Mendel (1866): particulate factors segregate and assort independently. Flemming (1882): described mitosis and chromosomes. Weismann (1880s): proposed continuity of chromosomes. Sutton (1902): observed grasshopper chromosomes during meiosis — noted parallels with Mendelian factors. Boveri (1902): sea urchin experiments showing different chromosomes have different effects. Sutton-Boveri Chromosome Theory: genes are physically located on chromosomes. Chromosomes occur in pairs (homologous) ↔ Mendel's factors in pairs. Chromosomes segregate at meiosis I → Law of Segregation (physical basis). Different chromosome pairs segregate independently → Law of Independent Assortment. Each chromosome carries many genes (linkage groups). Morgan's confirmation (1910): Drosophila work — linked genes on same chromosome. Sex-linked inheritance: genes on sex chromosomes. Recombination maps. Nobel Prize in Physiology or Medicine to Morgan (1933).
Go deeper
Morgan's crucial experiments: white eye gene in Drosophila located on X chromosome (sex-linked inheritance). Autosomal vs sex-linked inheritance: different patterns in cross (more males affected for X-linked recessive). Two genes on same chromosome: don't follow independent assortment → linkage → recombination frequency used to map gene positions. This physical mapping of genes to chromosomes definitively proved the chromosome theory.
From Class 10
Mendel described hereditary 'factors' without knowing their physical location. The chromosome theory of inheritance established that these factors (genes) are located on chromosomes.