Model Organisms - Drosophila melanogaster

Model Organisms - Drosophila melanogaster

• Drosophila melanogaster is a common model organism
• It belongs to the Order Diptera, Family Drosophilidae, and Genus Sophora
• It is found on every continent except Antarctica
• It is a powerful model organism due to its ease of care, many offspring, short generation time, and well-studied genome
• Its genome size is estimated at ~180 Mb
• It has four pairs of chromosomes; one pair of sex chromosomes (X and Y) and two pairs of autosomes and a small dot chromosome
• Its life cycle involves embryos, larvae (with 3 instar stages), pupae, and adults
• Gene expression during metamorphosis is mediated by the hormone ecdysone
• Larval tissues break down, and adult tissues develop from imaginal discs, which are tissue-specific progenitor cells
• Wild-type Drosophila feed on yeast, bacteria, and rotting plant matter
• In the lab, Drosophila are fed standardized diets consisting of cornmeal, yeast, and agar.
• Adult flies lay eggs on the food surface, and larvae burrow into the food.
• Wandering third instar larvae crawl out and pupate on the sides of vials.
• The first physical maps of Drosophila chromosomes were created by Calvin Bridges in 1935 using polytene chromosomes in the salivary glands
• Adding a chemical dye to polytene chromosomes creates unique banding patterns
• These regions were numbered and standardized

Sex Determination in Drosophila

• The presence of a Y chromosome does not directly determine sex in Drosophila
• Sex determination is regulated by an X chromosome counting mechanism, which "senses" the dosage of X chromosomes
• XO flies are males due to the decreased X dosage

Genome Features

• The genome assembly predicts 13,920 protein-coding genes.
• 72% of the genome is considered functional.
• More than half of Drosophila melanogaster genes exhibit alternative splicing.
• 45% of genes produce more than one protein.

Forward Genetics

• Work by the Heberlein lab identified genes associated with alcohol tolerance and alcoholism (barfly & tipsy)
• This demonstrated similarities in neural responses between Drosophila and humans

Reverse Genetics

• Analyse the phenotype of a gene by directly editing the gene
• This also includes Transgenics and UAS/Gal4 & P-elements

Transposable Elements

• Drosophila has ~150 families of transposable elements (TEs) in its genome
• TEs are often detrimental, as they can insert into genes and cause chromosomal rearrangements.
• The P element assisted in the development of many genetic tools

Transgenics

• Transgenics involve transferring foreign genes into the Drosophila genome.
• A common technique involves introducing the gene during pole cell budding

Gal4/UAS System

• This system allows for tissue-specific gene expression.
• The enhancer-trap Gal4 drives gene expression in specific tissues

Gene Knockout

• This technique involves disrupting specific genes to study their function.
• CRISPR-Cas9 is typically involved in modifying DNA

Further reading

• Core reading: Chapters 1 & 2: Heredity; Chapter 5: Linkage, Recombination, Gene mapping; Chapter 19: Manipulating the Genomes of Eukaryotes
• Extra reading: Chapter 22: Genetic Analysis of Development

Explore the fascinating world of Drosophila melanogaster, a widely used model organism in genetic research. Learn about its characteristics, life cycle, and significance in studies of gene expression and development. This quiz covers important aspects of its biology and practical applications in scientific research.