Drosophila fly article dating before 1950

Blending of traits in the progeny is now explained by the action of multiple genes with quantitative effects.Another theory that had some support at that time was the inheritance of acquired characteristics: the belief that individuals inherit traits strengthened by their parents.Although the structure of DNA showed how inheritance works, it was still not known how DNA influences the behavior of cells.

drosophila fly article dating before 1950-18

After the rediscovery of Mendel's work, scientists tried to determine which molecules in the cell were responsible for inheritance.

In 1911, Thomas Hunt Morgan argued that genes are on chromosomes, based on observations of a sex-linked white eye mutation in fruit flies.

A popular theory during the 19th century, and implied by Charles Darwin's 1859 On the Origin of Species, was blending inheritance: the idea that individuals inherit a smooth blend of traits from their parents.

Mendel's work provided examples where traits were definitely not blended after hybridization, showing that traits are produced by combinations of distinct genes rather than a continuous blend.

James Watson and Francis Crick determined the structure of DNA in 1953, using the X-ray crystallography work of Rosalind Franklin and Maurice Wilkins that indicated DNA has a helical structure (i.e., shaped like a corkscrew).

This structure showed that genetic information exists in the sequence of nucleotides on each strand of DNA.

The structure also suggested a simple method for replication: if the strands are separated, new partner strands can be reconstructed for each based on the sequence of the old strand.

This property is what gives DNA its semi-conservative nature where one strand of new DNA is from an original parent strand.

A classic example is two seeds of genetically identical corn, one placed in a temperate climate and one in an arid climate.

While the average height of the two corn stalks may be genetically determined to be equal, the one in the arid climate only grows to half the height of the one in the temperate climate due to lack of water and nutrients in its environment.

Although this pattern of inheritance could only be observed for a few traits, Mendel's work suggested that heredity was particulate, not acquired, and that the inheritance patterns of many traits could be explained through simple rules and ratios.

Tags: , ,