In: Biology
What is the importance of Drosophila melanogaster in genetic research?
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.