Lecture 11 - Dosophila as a development and genetic

Question 1

Describe the properties of a drosophila

Answer 1

• fly for several hours
• radius is >12km
• 1 mg

Question 2

What did drosophila melongaster ‘the fly’ get a nobel prize on?

Answer 2

genes on chromosomes are the basis of heredity

Question 3

What is a ‘centi-Morgan’?

Answer 3

if 2 genes are 1 centi-Morgan apart, they have a 1% chance of being segregated to different places

Question 4

Are drosophila a protostome or a deuterostomes?

Answer 4

protostomes - about 700 million years apart from humans as deuterostomes

Question 5

What are the genes that control development of a fly similar to?

Answer 5

genes that control the development of vertebrates

Question 6

What is forward genetics?

Answer 6

• 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

Question 7

What is reverse genetics?

Answer 7

starting with a gene (gene sequence known) - gene function needs to be determined. Occurs through knockout

Question 8

What is saturation screening?

Answer 8

• 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

Question 9

What is EMS?

Answer 9

a mutagen

Question 10

What do mutated genes need to be to show their phenotype?

Answer 10

homozygous - they screened 1000s of lines to find out functions of genes

Question 11

What do mutant screens lead to?

Answer 11

1. basic understanding of HOW genes are controlling & elaboration of a body plan
2. molecular identification of many new genes and cell-to-cell signaling pathways
3. confirmed ‘genetics’ as an extremely powerful way to dissect biological processes

Question 12

What genes and principles were found to be very similar in animals & humans?

Answer 12

genes that are important during development but often remain important throughout life - e.g. homeostasis, cancer, regeneration & ageing

Question 13

What is the life cycle of drosophila melongaster?

Answer 13

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

Question 14

What does a nuclear division create in drosophila?

Answer 14

syncytium - multiple nuclei in one cytoplasm

Question 15

What occurs after the formation of a syncycium?

Answer 15

• 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

Question 16

What do the pole cells form?

Answer 16

germline

Question 17

What occurs after the formation of the blastoderm?

Answer 17

gastrulation - formation of multiple internal cell layers

Question 18

What are the 3 parts that develop during gastrulation?

Answer 18

ECTODERM
MESODERM
ENDODERM

Question 19

What does the ectoderm form?

Answer 19

epidermis & nervous system

Question 20

What does the mesoderm form?

Answer 20

muscle

Question 21

What does the endoderm form?

Answer 21

gut

Question 22

What is aminoserosa?

Answer 22

embryonic tissue (disappear in development)

Question 23

Describe how gastrulation occurs

Answer 23

• 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.

Question 24

What takes places when germ-band extension occurs?

Answer 24

segmentation

Question 25

What can segmentation be broken down into?

Answer 25

thoracic segments, abdominal segments & mouthparts

Question 26

What occurs during metamorphosis?

Answer 26

• 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

Question 27

What has been used to explain how a number of patterning systems work?

Answer 27

wing

Question 28

Where are germline stem cells found?

Answer 28

at the tip of the testes and ovariole

Question 29

What are germline stem cells direct descendants of?

Answer 29

pole cells - set out early on in development

Question 30

What can occur during the screening stage?

Answer 30

• 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

Question 31

What is the dorsal side different from?

Answer 31

the ventral side

Question 32

What does a gap gene mutation lead to?

Answer 32

• 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.