Question

In: Biology

Drosophila melanogaster

What is the importance of Drosophila melanogaster in genetic research?

Solutions

Expert Solution

  • Drosophila melanogaster has been extensively studied over a century as a model organism for genetic investigations.

  • It has many characteristics which make it an ideal organism for the study of animal development and behavior, neurobiology and human genetic diseases.

  • A model organism needs to share on the molecular level many similar features and pathways with humans.

  • It turns out that approximately 60% of a group of readily identified genes that are mutated, amplified or deleted in a diverse state of human diseases have counterpart in Drosophila.

  • Studying these genes in drosophila led scientists to bypass some of the ethical issues of biomedical research involving human subjects.

  • The fruit fly has many practical features that allow scientists to carry out research with ease.

  • First of all a very short life cycle, ease of culture and maintainance and a low number of chromosomes.

  • A small genome size in terms of base pairs but giant salivary gland chromosomes known as polytene chromosomes.

  • The Female fruit fly about 3 mm in length will lay between 750-1500 eggs in her lifetime.

  • The life cycle of fruit fly takes only about 12 days to complete at room temperature.

  • After the egg is fertilized the embryo emerges in about 24 hours.

  • The embryo undergoes successive molds to become the 1st, 2nd and the 3rd instar larvae.

  • The larval stages are characterized by consumption of food and resulting growth followed by the crescent pupal stage during which there is a dramatic recognition of the body plan followed by the emergence of the adult fly.

  • Because the flies themselves are quite small, near about 1mg, we can raise a lot of them at once.

  • Traditionally, flies have been raised in quarter pint milk bottles using a well ripened banana as food although more often our cornmeal agar mixture is now used.

  • Genetic experiments can be done in a shell vial with just a few flies.

  • Thus, many different mutant stocks can be maintained and numerous experiments carried out.

  • In a small lab space,when large amounts of material are needed, large population cages which hold upto 50,000 flies in a cage which means that scientists can collect and harvest 100's of grams of embryos larvae or adults at a time.

  • The material can be frozen in liquid nitrogen and then used as the starting point for preparing enzymes such as RnA polymerase 2 or for purifying chromosomal proteins such as histones or for analysis of chromatin structures.

  • The genetic information in all cells is carried in the chromosome packed in the cell's nucleus as with humans.

  • The chromosomes of Drosophila melanogaster come in pairs but unlike humans which have 23 pairs of chromosomes.

  • The fruitfly has only 4, a pair of sex chromosmes together designated one along with 3 pairs of autosomes labelled 2 through 4. 

  • Chromosome 4 is the smallest and is also called the dot chromosome.

  • It represents just about 2% of the fly genome.

  • The low manageable number of chromosomes was a key attraction of the organism in early genetic studies.

  • Indeed some classic genetic analysis of mutations and mapping of mutants of specific chromosomes in drosophila were used to determine the ground rules for the transmission of genes.

  • In terms of base pairs the fly genome is only 5% of the size of the human genome i.e., 132 million base pairs for the fly compared with 3.2 billion base pairs for the human.

  • In terms of the number of genes, however the comparison isn't nearly so lopsided.

  • The fly has approximately 15,500 genes on its 4 chromosomes, whereas humans have about 22,000 genes among their 23 chromosomes.

  • Thus the density of the genes per chromosome in Drosophila is higher than for the human genome.

  • Humans and flies have retained the same genes from their common ancestors over about 60% of their genome.

  • Based on an initial comparison approximately 60% of genes associated with human cancers and genetic disease are found in the fly genome.

  • The parallels between the genomes of Drosophila and humans are central to using this tiny flies to explore human development behavior and genetic disease.

  • Often the genes associated with these attributes in humans have closely matched fly counterparts.

  • There are many examples of conditions in drosophila that are parallel to human conditions.

  • This can provide an opportunity to study the function of these genes and perhaps help the development of valuable drugs.


 

  • Drosophila melanogaster is commonly called Fruit fly.

  • It is widely used for genetic research.

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