Linkage Mapping in Drosophila
Common fruit flies, D. melanogaster, have been found as one of the most useful tools in genetic research. The reason behind that it is a popular experimental organism is due to the high likely hood of producing mutant, visible individuals. Geneticist, Thomas Morgan Hunt, was the first to discover the Drosophila as a model organism to study genetic hereditary. His research showed that the species could randomly obtain genetic mutations that could be visible in the parental generation.
Since fruit flies have a diploid chromosome number of 8 (haploid 4), chromosomal types are easily identified. Various genetic crosses are able to ...view middle of the document...
This experiment will test the hypothesis: Reciprocal crosses of D. melanogaster will show that all of the x-linked mutations will not assort independently while autosomal mutations assort independently. Based on analysis of the data, it will conclude if the hypothesis can be rejected or accepted.
This experiment was performed from the website, http://biologylab.awlonline.com/. The first portion of the experiment determines what type of alleles the unknown mutations were by simple reciprocal crosses. Reciprocal crosses of mutant females and wild type males (and vice versa) are analyzed to see if the progeny of the cross showed the mutant allele as being recessive or dominant as well as autosomal or x-linked. The results of the reciprocal crosses were deciphered by following Table A.
|If the mutation is: |Offspring of the cross : |Offspring of the cross : |
| |Mutant ♀ x Wild type ♂ |Wild ♂ & Wild ♀ |
|Recessive and autosomal |Wild ♂ & Wild ♀ |Wild ♂ & Wild ♀ |
|Dominant and autosomal |Mutant ♂ & Mutant ♀ |Mutant ♂ & Mutant ♀ |
|Recessive and X-linked |Mutant ♂ & Wild ♀ |Wild ♂ & Wild ♀ |
|Dominant and X-linked |Mutant ♂ & Mutant ♀ |Wild ♂ & Mutant ♀ |
Once the mutation was typed, a three factor test cross was performed on all the x-linked mutations to determine the order and map distance of chromosome 1. In order to perform a three factor test cross, the female must be heterozygous since crossing over in fruit flies only occurs in the female species. On the other hand, the male fruit fly is recessive for all three genes. The number of offspring was recorded and the phenotypes were arranged in pairs to determine if the classes were nonrecombinant or double crossovers. Once the classes are determined, the two classes are compared to find out the gene that was switched in the double crossover. This gene was the gene in the middle for the order. The remaining genes were placed to right and left of this gene. In order to calculated map distance, coefficient of coincidence, and interference, the single crossover classes must be compared to the nonrecombinant classes to determine what gene was switched. Finally, the chromosomal number was determined for the autosomal chromosomes. Several different test crosses were done to determine if the mutation was on chromosome 2 or 3. If the chromosome did not come up positive for chromosome 2 or 3, then it will be located on chromosome 4. All x-linked mutations are...