Book Viewer

Short Contents | Full Contents | Other books @ NCBI

Modern Genetic Analysis Chapter 5. Recombination of Genes Linkage Maps
Genetics In Process 5-2: The first chromosome map

Alfred Sturtevant began his career in genetics in 1911 as an undergraduate in the lab of the great geneticist Thomas Hunt Morgan. Morgan assigned Sturtevant the task of making sense of some data showing various allelic combinations arising from crosses of genes showing X chromosomelinked inheritance. In one evening Sturtevant made sense of all the data and in doing so developed the analytical method for mapping genes on chromosomes that is still used today. In a later recollection he says

In the latter part of 1911, in conversation with Morgan, I suddenly realized that the variations in the strength of linkage [association between alleles of different genes], already attributed by Morgan to the spatial separation of genes, offered the possibility of determining sequences in the linear dimension of a chromosome. I went home and spent most of the night (to the neglect of my undergraduate homework) in producing the first chromosome map

The analysis was published in 1913. The introduction states

The parallel between the behaviour of the chromosomes in reduction, and that of Mendelian factors in segregation was first pointed out by Sutton (1902) although earlier in the same year Boveri (1902) had referred to a possible connection.

The paper went on to map six X-linked genes using the following logic:

The proportion of "crossovers" could be used as an index of the distance between any two factors. Then by determining the distances (in the above sense) between A and B and between B and C, one should be able to predict AC. For, if proportion of crossovers really represents distance, AC must be approximately either AB plus BC or AB minus BC, and not any intermediate value.

Sturtevant's map of the X chromosome (the first genetic map) was as follows, in which the zero mark is one arbitrarily determined end of the map:

Note that (for example) the map distance between the rudimentary wing and miniature wing genes is 57.6 minus 33.7, or 23.9 map units.

Sturtevant's conclusion was

They [the results] form a new argument in favour of the chromosome view of inheritance, since they strongly indicate that the factors investigated are arranged in a linear series, at least mathematically.

Robert Calentine/Visuals Unlimited.

© 1999 by W. H. Freeman and Company. All rights reserved.