Lecture 6- Introduction to drosophila Flashcards
What are advantages and disadvantages of drosophila as a model organism?
Advantages: accessible embryology and adult developmental stages, low cost, fast, excellent genetics, no ethical concerns
Disadvantages: not a vertebrate and kept as live stock
Briefly outline the lifecycle of drosophila
- Fertilised egg undergoes cleavage to form a syncitial blastoderm
- Gastrulattion occurs to form a segmented embryo
- Embryo hatches out as feeding larva and growth through two more rounds of instars
- Eventually a pupa is formed which will metamorphose into an adult fly
What was discovered by Morgan in 1910?
White eyed flies
What was constructed by Sturtevant in 1913?
First genetic map with genes arranged in a linear order
What did Bridge show in 1914/16?
That chromosomes must contain genes
What was identified from saturation mutagenesis screens in 1987/80?
Identified genes involved in the development and patterning of the larval cuticle
What techniques were used more recently in Drosophila studies?
- P-element transformation- transgenics
- Enhancer/promoter traps
- Gal4/UAS system- gene misimpression
- FLP/FRT- clonal mutant analysis
- RNAi
- Omic technologies
What was released regarding Drosophila in 2014?
Genome- 137.6Mbp on 7 chromosome arms
What does knowing the Drosophila genome sequence allow?
- Make estimates of evolution
- For example take other closely related flies genomes and aline against drosophila melanogaster ptp61F gene
- Allows you to see untranslated exon, protein coding exons and introns
- If you align these regions between different species, you show the degree of similarity
- Protein coding exons specifically show very little change between species and are conserved as protein is needed to survive
- Most intron regions aren’t conserved among species
- Few intron regions that are conserved and are likely to be control regions/regulatory domains to ensure the correct gene expression at the correct time
How does the size of Drosophila males compare to females?
Male Drosophila are smaller than females with smaller abdomens
Outline the mating and gametogenesis of Drosophila
Mating and egg laying occurs in less than 2 weeks and produces over 200 eggs
Describe Drosophila courtship
Orientation - tapping - wing vibration - licking - attempted copulation
- Female will store sperm in specialised structures in the abdomen and is able to lay eggs the rest of her life (without the need to mate again)
- Strongest most reproducible behaviour is genetically encoded
Describe spermatogenesis
- Spermatogenesis occurs in males within the testes located in the abdomen
- The tip of the testes contains germ line stem cells located adjacent to the hub
- Hub cells secrete factors e.g unpaired- JAK/STAT pathway ligand
- As stem cells divide, daughter cells furthest away from the hub differentiate and further divisions will give rise to mature sperm
- Stem cells are maintained by activation of the JAK/STAT pathway. Disruption of this pathway leads to the loss of stem cells
- Sperm tails are very long and when mating occurs, the majority of ‘stuff’ transferred is sperm tails which prevent being responsive to a second courting attempt
- Males have made sex peptide which transfers with the sperm tails and dissolves in female blood stream and modifies her brain to become unresponsive to future courtship behaviour after she has mated
- However, females have anti-peptides to try and prevent this interaction
- This evolutionarily results in sperm tails getting progressive longer to try to counteract the anti-peptides released by the females
Describe oogenesis
- Females only need to mate one
- Abdomen contains 2 ovaries (with many ovarioles) and connect via oviduct
- Sperm is stored in the seminal receptacle
- As the eggs mature, they move down the oviduct, are fertilised and laid in the uterus
- Eggs ‘drilled’ into food when laid
- In ovarioles, there is a sequence of eggs as they develop through time
- In the tip, there is a population of stem cells (which are maintained by the JAK/STAT pathway)
- The stem cells which are not being maintained at the ovariole tip, divides and divides to many cells and form a germline cyst (4 x incomplete cystoblast mitotic divisions
- Divisions are not complete and the cells remain connected by bridges
- One cell will become the oocyte, the others will become nurse cells
- Selection of future oocyte: chosen oocyte will have diploid nucleus and undergo meiotic recombination before fertilisation
- Nurse cells will undergo endo-reduplication (DNA replication without cytokinesis) and provide maternal contributions for the fertilised egg
- Oocyte is surrounded by nurse cells which are surrounded by follicle cells and overtime this complex grows
- Nurse cells scarifies themselves to feed the growing oocyte/egg
- Egg activation by meiosis I and II
- Sperm fuses with female pro-nucleus
What are puffs in polytene chromosomes?
Extremely active genes
