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Mapping of Drosophila Melanogaster incomplete gene

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  1. Introduction
  2. Experimental Plan, Observations and Analysis
  3. Dihybrid cross to determine linkage on chromosome
  4. Discussion
  5. Conclusion

Gene mapping is the process of assigning gene to specific chromosomes or specific loci on that chromosome. It also determines the relative distance between genes linked on the same chromosome (Strachan & Read 2004). Gene mapping is used to construct linkage map that shows the relative locus of all genes on each chromosome. This allows discovery of genetic markers or DNA sequences that are readily identifiable under microscope observation. By doing so, locations of critical genetic elements that are responsible for a disease could be identified. In humans, information of inheritance pattern and disease system obtained solely from pedigree analysis are limited, as sufficient progeny are not available to give reliable confirmation on characteristics and inheritance mode of disease-causing genes. Missing individuals or erroneous information in the pedigree further hinders analysis. Modern genetic linkage are particularly useful, as it can be examined in collaboration with pedigree to maximize information that can be collected to infer likely genotypes of any missing individuals.

According to Mendel's principle of independent assortment, pairs of alleles for a gene are assorted independently into gametes during meiosis, independent of other genes. This means that the behavior of one allele on one chromosome is unaffected by that of another allele on different chromosomes, giving a typical 9:3:3:1 phenotypic ratio for dihybrid crosses. However, it only considers segregation of genes located on different chromosomes.

[...] Lastly, genetic mapping technique dictated the success of Human Genome Project which was completed in year 2004. A collaborated effort by international scientists, base sequence and all genes of human DNA were mapped completely and information are beneficial to many fields such as medicine and evolutionary studies. As aforementioned, this genome project allows us to better understand the cause of diseases and from there we can device effective treatments. Medications can be designed and their effects can be accurately predicted by looking at the molecular pathway associated with particular genes. [...]


[...] Full dihybrid cross date for Chromosome X linkage: Table 30: Number of F1 progeny resulting from cross between P11 (wild type female) and P12 (forked bristle, incomplete wing vein male) with respect to their phenotypes and sex. All F1 progeny had wild type eye and wing vein. No forked bristle, incomplete wing vein flies were observed. Table 31: Number of F2 progeny resulting from test cross between F1 wild type female and P12 (forked bristle, incomplete wing vein male) with respect to their phenotypes and sex. The ratio of dihybrid testcross for the forked bristle gene and incomplete wing vein gene follows the expected Mendelian's inheritance ratio of 1:1:1:1. [...]


[...] This was confirmed using Chi-square analysis based on null hypothesis that independent assortment occurred which ultimately was rejected. Mendelian ratio was not obeyed because both ebony and incomplete wing vein genes were inherited as single unit during meiosis, giving rise to resulting in two parental combinations namely wild type and ii) incomplete wing vein and ebony body, as well as recombinant combinations namely ebony body and ii) incomplete wing vein. The recombinants was due to crossing over events that occur between homologous chromosomes. [...]


[...] Full dihybrid cross data for Chromosome 4 linkage: Table 25: Number of F1 progeny resulting from cross between P9 (wild type female) and P10 (eyeless, incomplete wing vein male) with respect to their phenotypes and sex. All F1 progeny had wild type eye and wing vein. No eyeless, incomplete wing vein flies were observed. Table 26: Number of F2 progeny resulting from cross between F1 wild type female and P10 (eyeless, incomplete wing vein male) with respect to their phenotypes and sex. [...]


[...] It is not X-linked and is located at chromosome between sepia eye gene and ebony body gene. The map distance between sepia eye and incomplete wing vein is 17.87 mu, while between incomplete wing vein and ebony body is 19.16 mu. The map locus of incomplete wing vein gene is 43.87 mu. References: Bina M 2006, ?Methods for Identifying and Mapping Recent Segmental and Gene Duplications in Eukaryotic Genomes', in Methods in Molecular Biology: Gene Mappings, Discovery, and Expression-Methods and Protocols, Humana press Inc., New Jersey, pp. 9-21. [...]

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