GENETICS

The Chromosome Theory of Inheritance

1902 to 1915 CE

Phanerozoic · Cenozoic · Quaternary · Holocene · Meghalayan

The chromosome theory of inheritance, developed between 1902 and 1915, states that Mendel's abstract units of inheritance lie on chromosomes, thread-like structures in the cell nucleus.

The chromosome theory of inheritance states that Mendel's units of inheritance, until then abstract, are located on chromosomes. Chromosomes pair, separate and are distributed exactly as Mendel's units behave. This parallel was drawn in 1902, and it remained an analogy until a white-eyed fruit fly appeared in a laboratory at Columbia University. Morgan (1910) observed that the white eyes were inherited together with the chromosome that determines sex, a pattern called sex linkage. The trait appears in males and females in different proportions, and only a unit located on that chromosome explains the difference.

Why it matters

Heredity ceased to be a statistical rule and became an object. A gene, the unit of inheritance, occupies a definite position on a definite chromosome, and that position can therefore be mapped. Everything that follows in this part of the timeline depends on that localisation of the gene, from the double helix, the structure of DNA, to genome editing, the deliberate modification of an organism's DNA.

Dating & uncertainty

Sutton and Boveri proposed the connection between Mendel's units and chromosomes in 1902 and 1903. The connection remained contested until the fruit fly work of 1910 to 1915, which linked particular traits to particular chromosomes.

Earth history as one day

23:59:59.99762.4 ms before midnight

if Earth’s 4.54 billion years were compressed into a single day