Drosophila

Question 1

1. state 4 advantages of using drosophila in biomedical research
2. state 2 disadvantages of using drosophila in biomedical research

Answer 1

1. • small organisms therefore they are easy and cheap to keep
   • short generation time
   • large number of embryos produced
   • sequenced genome
2. • small organisms therefore tissue manipulation is difficult
   • invertebrates, therefore they are distantly related to humans

Question 2

name 2 temperatures that drosophila are kept at, and the effects that these temperatures have on the length of development

Answer 2

1. 25^oC (where development is 10 days)
2. 18^oC (where development is >21 days)

Question 3

1. how long does it take to go from a fertilised egg to a sexually mature adult?
2. what process gives rise to the syncytial blastoderm?
3. What do the pole cells give rise to? When and how are they set aside?
4. after how many hours post fertilisation does gastrulation occur?
5. what also occurs during gastrulation?
6. After how many hours post fertlisation is a fully segmented larvae produced?

Answer 3

1. 10 days
2. nuclear division without cytokinesis
3. the germ cells. they are set aside during the syncytial phase when a few nuclei move to the posterior end of the embryo and become cellularised
4. 3 hours
5. germ band extension
6. 10 hours

Question 4

1. name the 3 defined regions of a hatched larvae.
2. are imaginal discs present in the hatched larvae?
3. How many times does the larvae shed its outer layer? What is this called?
4. What happens to the 3rd instar larvae?

Answer 4

1. acron, telson and denticle belt
2. yes
3. twice. instar
4. it pupates and undergoes metamorphosis

Question 5

1. during the saturation mutagenesis performed in 1980, how many genes involved in the development and patterning of the larval cuticle?
2. how many chromosomes does the drosophila genome contain? How many genes does it contain? The Y chromosome is essentially what?
3. comparisson of the drosophila genome with the genomes of other organisms that what 2 things are conserved?

Answer 5

1. 139
2. 4 pairs (XY pair and 3 autosomal pairs); 16000 genes; essentially heterochromatin
3. protein coding regions as well as introns (which are probably gene regulatory sequences)

Question 6

1. why is courtship behaviour strongly reproducable behaviour?
2. name the 6 courtship behaviours of drosophila

Answer 6

1. because it is genetically encoded
2. orientation | tapping | wing vibration | licking | attempted copulation | intercourse

Question 7

1. what are sperm tails coated in? What does this substance do?
2. where abouts in the testes does spermatogenesis occur?
3. how do hub cells influence stem cells and differentiation of sperm?
4. how do somatic stem cells arrange themselves around germline stem cells

Answer 7

1. sex peptide. It makes females less responsive to the courtship behaviour of competing females
2. in the tip
3. hub cells secrete the JAK/STAT pathway ligand, which influences surrounding cells to remain as stem cells. Cells adjacent to the hub cells receive more ligand therefore remain as stem cells while cells further away recieve less signal thus differentiate into sperm
4. somatic stem cells form capsules around sperm stem cells.

Question 8

1. describe the pathway of the egg from production to being laid.
2. where are germline stem cells found within the ovary?
3. how does a germline stem cell become differentiated into an egg?
4. what do nurse cells and the oocyte and the nurse cells become surrounded by? What does this form?
5. What are these cells (Q4) involved in and how?
6. What is the name of the process where nurse cells undergo DNA replication without nuclear or cell division?
7. How are proteins and RNA made by the nurse cells that are required for growth and development transferred into the oocyte?

Answer 8

1. egg produced and released by ovarioles into the oviduct where it decends into the uterus. In the oviduct, sperm stored in the spermatheca fertilise the egg.
2. the tip
3. 16 cells are produced bt 4 divisions. 2 of these cells make 4 connections with other cells. One of these cells undergoes mitosis to form the oocyte. the 15 other cells become nurse cells
4. follicle cells, forming the egg chamber
5. early patterning of the oocyte. They become divided into different subpopulations around the oocyte, which express different genes that have different effects on the oocyte?
6. endoreduplication.
7. cytoplasmic dumping via ring canals

Question 9

1. what is responsible for the subcellular localisation of maternal factors that governs oocyte patterning?
2. what is this dependent on?
3. how is maternal RNA transported within the cell in response to what? use bicoid as an example
4. what do follicle cells produce? (2)

Answer 9

1. reorganisation of the microtubule cytoskeleton
2. posteriorly localised PAR proteins
3. positive/negative motor proteins in repsonse to a signal (e.g. bicoid is transported using dyenin in response to the gurken signal
4. chorion and vitelline membrane

Question 10

1. how many segments do drosophila have? What is the characteristic of each?
2. what does each segment have?
3. When does segmentation occur?

Answer 10

1. 14: 3 head, 2 thoracic and 8 abdominal
2. polarity - naked cuticle and denticle belt
3. embryogenesis

Question 11

1. what is the phenotype of the bicoid mutant?
2. what is the phenotype of the knirps mutant?
3. what is the phenotype of the paired mutant?
4. what is the phenotype of the gooseberry mutant?

Answer 11

1. lack of anterior structures
2. loss of A2-A7 segments
3. loss of every other segment
4. loss of part of each segment

Question 12

name the 4 classes of genes that influence segmentation

Answer 12

1. maternal genes
2. gap genes
3. pair rule genes
4. segment polarity genes

Question 13

1. describe the distribution of bicoid throughout the syncytial blastoderm
2. what does bicoid act as?
3. what are high affinity sites activated by? Where does this occur?
4. What are low affinity sites activatedy by? where does this occur?

Answer 13

1. a gradient, with high concentration at the anterior end and a low concentration at the posterior end
2. a morphogen
3. lower bicoid concentration; middle of the embryo
4. higher bicoid concentration; anterior end of embryo

Question 14

1. what is the activity of gap genes determined by?
2. name 4 gap genes. In what pattern are these genes expressed?
3. Name the gene that influences the expression of gap genes. How do the gap genes respond to this gene, in respect to the pattern of expression. Give example

Answer 14

1. gradient of maternal factors
2. giant, kruppel, knirps and tailless. They are each expressed in bands
3. Hunchback. Each gap gene has a different sensitivity to hunchback, therefore is only expressed in the region of a certain concentration of Hunchback. E.g. Kruppel is repressed at high concentrations and very low concentrations, but expressed at a moderate concentration of hunchback.

Question 15

Pair Rule Genes

1. in what pattern are these genes expressed?
2. how is this pattern specified?
3. what is the expression dependent upon
4. are the regulatory complexes of these genes complex or simple?

Answer 15

1. expressed in stripes in every other segment
2. each stripe is specified independently
3. dependent upon the interraction of positively and negatively acting transcription factors (i.e. the combination of TFs in each segment)
4. complex

Question 16

1. name 2 segment polarity genes
2. what is the role of segment polarity genes
3. name the pair rule gene which induces the expression of one of these genes and where in the segment it is expressed
4. describe how the genes mentioned in Q1 maintain each others expression. What does this feedback loop do?

Answer 16

1. Hh and Wg
2. define the AP regions of each segment
3. Engrailed. It is expressed at the anterior border of the posterior parasegment
4. engrailed induces Hh expression in the same cells. Hh is secreted and acts anteriorly. It induces the expression of Wg in the cells at the posterior border of the anterior parasegment. Wg is secreted and acts posteriorly to maintain Hh expression. This feedback loop defines the segment borders

Question 17

1. how do other insects become segmented?
2. Which signalling pathway is implicated? How are the signalling components expressed?
3. describe how a new segment is formed.

Answer 17

1. They start off with head and thoracic segments; extra posterior segments are added sequentially due to the budding off of the posterior disc
2. notch, It is expressed in rings in the tail region, in an oscilatory circuit.
3. Adjacent stripes of delta and her set up a feedback loop in an oscilatory pattern, the wave of which produces the segments

Delta activates notch which activates Her. Her downregulates itself, and delta so tat the adjacent cell receives a weaker signal thus less delta is downregulated.