Talk:Alfred Sturtevant

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I remember reading about a unit called a "sturt", named for Sturtevant, which is similar to a morgan but measures distances in embryos. It was in a Scientific American article about fruit flies, and they found the point where a gene is expressed by making a two-cell embryo with the gene and a marker gene expressed in one cell, letting it grow, and finding the probability that only one of the two genes is expressed in the fly. Can someone else verify this? -phma 01:02, 23 December 2005 (UTC)
 * Found one: http://www.uni-kl.de/FB-Biologie/AG-Cullum/Teaching/Files/Gen1Lec3.pdf -phma 00:30, 2 January 2006 (UTC)
 * There's now an article Sturt (Biology) but it is so far just a link to the wiktionary definition. RJFJR (talk) 14:08, 30 October 2010 (UTC)

Other noteworthy contributions of Sturtevant
Moved to talk because it is just a list (almost of trivia) that should be gone over and important items integrated into the article rather than left as a badly formatted list. RJFJR (talk) 14:08, 30 October 2010 (UTC)

•	He discovered unequal crossing over – one chromosome breaks so that it yields two crossovers
 * Did a cross of certain eye/wing characteristics produced only 6 phenotypes when it should have produced 8. This showed that 3 of the phenotypes (and hence genotypes) were linked – to interpret results, you must assume that the genes are arranged on the chromosome in a specific order. The cross test tells us the sequence of the genes.
 * Theorized that consistency of crossover values and the constant order of genes on a chromosome means that a gene occupies a fixed position in a chromosome, and the allele has the corresponding position in the homologous chromosome. The intervals between adjacent loci are crossover regions and are numbered from left to right. A chromosome map, therefore, is a chart that illustrates the spacing of the genes on a chromosome. He defined a map unit as a distance that will give (on average at standard conditions) one crossover per 100 gametes.
 * Sturtevant was a supporter of the chromosome theory of inheritance: "several explanations of linkage have been advanced in the past, but it is now quite clear that the correct interpretation is that genes are linked because they are carried on the same chromosome". (Sturtevant, An Introduction to Genetics p. 66)
 * Discovered that single chromatids do not cross over.
 * Invented fate mapping, which reveals how certain cells develop and most importantly where they end up in the body.
 * Sturtevant suddenly realized that the variations in strength of linkage, already attributed by Morgan to differences in 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, which included the sex linked genes y, w, v, m, and r, in the order and approximately the same relative spacing that they still appear on the standard maps" (Sturtevant, A History of Genetics p. 47).
 * "By 1915 the work with Drosophila had progressed to the point where the group at Columbia was ready to try to interpret the whole field of Mendelism in terms of the chromosome theory. The resulting book, The Mechanism of Mendelian Heredity (Morgan, Sturtevant, Muller and Bridges, 1915), is a milestone in the history of the subject". (Sturtevant, A History of Genetics p48-49).
 * There was still much exciting and fundamental work to be done with Drosophila…but it had become a question of how the chromosome mechanism worked, not of whether it could be demonstrated to be the true mechanism” (Sturtevant, A History of Genetics 49)

•	Morgan proposed (in 1911, after Sturtevant’s work/invention) that linkage is due to genes being on same chromosome (alleles being on same pair of chromosomes) – closely linked genes closer on chromosome - “Here, then, in 1911, was the essence of the chromosome interpretation of the phenomena of inheritance” (Sturtevant, A History of Genetics 44)

•	Sturtevant’s most famous and revolutionary discovery, chromosome mapping, has many important uses in modern biology:

•	each chromosome has a banding pattern; numbered to help identify regions of a particular chromosome •	chromosome maps have allowed for the development of karyotypes/karyotyping

•	chromosome maps allows us to know where the gene for a particular trait is (ex – glaucoma on 1st chromosome – knowing location of gene allows for development of genetic tests

•	helpful in establishing genome testing

•	chromosome mapping details the position and spacing of “biochemical landmarks” (ex- genes)

•	modern geneticists still use Sturtevant’s technique of mapping & his same map unit: 1 map unit = 1% frequency of recombination

•	Mapping genes and linkage maps have important applications for medical screening. For example, the muscular dystrophy gene DS is linked by 10 map units to the S locus, coding for a specific antigen that can be detected immunologically. These genetic tools are also quite useful for indirect selection of desirable traits (for example, disease resistance), on the basis or linked markers in practical breeding. Maps are also used for evolutionary inferences among related species and for other fundamental research programs. The new field of genomics started with the gene mapping work of T. Morgan. (Quiros) “Using the molecular techniques developed by the children of Morgan, his scientific children, they identified an abnormal mutation in a gene encoding a protein that was quite well known called synuclein, and that has proved enormous[ly] helpful in out analysis of the mechanisms of Parkinson’s Disease” (Edelman 6).

•	discovered chromosome inversion: a segment of a chromosome is turned upside down and reattached to the chromosome

•	balanced inversion occurs if all of the genes normally present in the uninverted chromosome are still present in the inverted chromosome; if genes get lost or duplicated, inversion is unbalanced – this can cause birth defect

•	Sturtevant’s discovery of inversion is important because it explains the why/how of certain genetic defects and discovery of inversion allows for its presence to be tested for

•	Genetic tests exist today for some disorders caused by inversions

Segregating genes?
The text contains a reference to "segregating genes", which is a concept I see thrown about without having found a good definition of. Is it the same as "segregating alleles"? Maybe that link could be added in that case. 83.241.192.2 (talk) 08:43, 26 March 2014 (UTC)

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