Lecture 11 - Dosophila as a development and genetic Flashcards
Describe the properties of a drosophila
- fly for several hours
- radius is >12km
- 1 mg
What did drosophila melongaster ‘the fly’ get a nobel prize on?
genes on chromosomes are the basis of heredity
What is a ‘centi-Morgan’?
if 2 genes are 1 centi-Morgan apart, they have a 1% chance of being segregated to different places
Are drosophila a protostome or a deuterostomes?
protostomes - about 700 million years apart from humans as deuterostomes
What are the genes that control development of a fly similar to?
genes that control the development of vertebrates
What is forward genetics?
- find the mutant phenotype first then find out the particular function. We know the function we don’t know the sequence.
- if a gene that control development is deactivated, it should lead to development defects that will illustrate its function
What is reverse genetics?
starting with a gene (gene sequence known) - gene function needs to be determined. Occurs through knockout
What is saturation screening?
- in order to make a mutation, a chemical (EMS) was used - acts at random
- this treatment was adjusted such that an average gene would be destroyed with a chance of 1 in 500
What is EMS?
a mutagen
What do mutated genes need to be to show their phenotype?
homozygous - they screened 1000s of lines to find out functions of genes
What do mutant screens lead to?
- basic understanding of HOW genes are controlling & elaboration of a body plan
- molecular identification of many new genes and cell-to-cell signaling pathways
- confirmed ‘genetics’ as an extremely powerful way to dissect biological processes
What genes and principles were found to be very similar in animals & humans?
genes that are important during development but often remain important throughout life - e.g. homeostasis, cancer, regeneration & ageing
What is the life cycle of drosophila melongaster?
9 days for it to form from fertilised egg to reproducing adult.
24 hours larvae hatch (first instar larvae)
- hatch for a second time (second instar larvae)
- hatch for a third time (third instar larvae)
- then become pupa
metamorphosis occurs leading to the development of an adult fly
What does a nuclear division create in drosophila?
syncytium - multiple nuclei in one cytoplasm
What occurs after the formation of a syncycium?
- within 90 mins - nuclei migrate to periphery of cytoplasm
- 2 house Syncytial blastoderm leads to development of pole cells
- pole cells develop the germ-line - they will make the next generation of flies
- 3 hours post fertilisation the embryo consists of a single layer of cells enclosing the yolk (containing a few nuclei)
- at the posterior of the embryo - the POLE CELLS are separated off - these will form the germline
What do the pole cells form?
germline
What occurs after the formation of the blastoderm?
gastrulation - formation of multiple internal cell layers
What are the 3 parts that develop during gastrulation?
ECTODERM
MESODERM
ENDODERM
What does the ectoderm form?
epidermis & nervous system
What does the mesoderm form?
muscle
What does the endoderm form?
gut
What is aminoserosa?
embryonic tissue (disappear in development)
Describe how gastrulation occurs
- gastrulation starts on the ventral area of the embryo, before invagination leads to the development of the gut system.
- a second movement then occurs, where the ventral cells elongate and extend over the dorsal.
- This is called GERM-BAND EXTENSION
- after germ band extension, GERM-BAND EXTRACTION occurs.
What takes places when germ-band extension occurs?
segmentation
What can segmentation be broken down into?
thoracic segments, abdominal segments & mouthparts
What occurs during metamorphosis?
- number of imaginable discs have a particular function that will form a particular structure in the adult fly - e.g. wing, mouthparts, leg, genitalia, eye
What has been used to explain how a number of patterning systems work?
wing
Where are germline stem cells found?
at the tip of the testes and ovariole
What are germline stem cells direct descendants of?
pole cells - set out early on in development
What can occur during the screening stage?
- used larvae to look at patterning, as end part of the larvae has unique structures - each segment has a characteristic pattern of denticles.
- denticles have a particular orientation - allowing recognition of anteroposterior polarity in each segment
What is the dorsal side different from?
the ventral side
What does a gap gene mutation lead to?
- some parts of the segments are missing
- this means wherever the mutation is, it is involved in the mutation of these segments that haven’t developed.
