lecture 6 Flashcards
What are the adv and dis of using mice as model organisms?
Adv= not too big, are mammals and vertebrates Dis= very expensive to keep, require a licence, long generation time (90 days)
What are the adv and the dis of using chicks as model organisms?
Adv= accessible embryology, cheap to keep, vertebrates Dis= unable to carry out genetics and need licence
What are the dis and adv of using zebrafish as model organisms?
Adv= accessible embryos and relatively cheap Dis= ethics and not amazing genetics
What are the adv and dis of using drosophila as model embryos?
Adv= very cheap, no ethics, fast generation time, accessible embryo, excellent genetics Dis= not a vertebrate
Describe the life cycle of a drosophila
Embryo- syncytial blastoderm- larva- pupa- adult. They shed their skin twice due to out growing their skin. First 3hrs= will be segmented germ layer
Females mate 8-9 hours after emerging and will lay eggs 1 day later. Life expectancy is around 2 months
Give a brief history to the scientists involved in fly genetics
1) Thomas Hunt Morgan 1910= began experimenting with drosophila after he captured a white eyed fly
2) stratevant 1913= developed the first genetic map- found that DNA was a code
3) Bridges 1913/14= DNA was hereditary
4) Mullar 1927= X-rays cause mutations
5) Volhard and Wischaus 1979= carried out genetic screens and mutated the genome of the drosophila
6) 80s, 90s, 00s= misexpress genes and use transgenesis for genetic manipulation
What are the 7 chromosomes of drosophila and how many bps are there
X, 2L, 2R, 3L, 3R, 4, Y= 137.6mbps
There’s around 144 mbps of DNA sequenced from drosophila. What are the remaining 1.5 mbps?
heterochromatin
What can genome sequencing of invertebrates tell us about evolution?
Can make trees to see interrelatedness by comparing homologues and assess how evolved they are. Can see that species that diverged 3.4 million years ago are still closely related. Can see that introns mutate more frequently thus changing enhancer and promotor sequences
How do flies mate and what does it tell us?
They have a lot of behaviours e.g. licking, tapping, orientation etc. Can produce over 200 progeny in 2 weeks. This behaviour isn’t learned meaning that it is genetic
Describe drosophila spermatogenesis
Hub cells secrete unpaired onto stem cells closest to it to maintain their stem cell fate via the JAK/STAT pathway. The cells furthest away go on to differentiate to give rise to a cluster of 64 sperm cells.
describe drosophila oogenesis
Sperm in stored in the seminal receptacle in the female. The stem cells undergo 4 lots of cystoblast mitotic divisions- only 1 will form the oocyte. Go from germarium to cyst to egg chamber to follicle cell to oocyte. The nurse cell is large to supply the egg. It undergoes endo-reduplicant DNA replication. The oocyte is diploid and undergoes meiotic recombination when activated by the sperm
What are polytene chromosomes and how can they be observed?
They are duplicated DNA that aren’t in separate chromosomes- can be seen using ISH by labelling the DNA with a probe to observe gene function and location. See many fat bands due to transcriptional machinery
What are the maternal contributions to oocytes?
The nurse cells produce RNA and proteins that are delivered to the oocyte via ring canals- oocyte grows and the nurse cells shrivel and eventually die. The cytoskeleton contributes to subcellular localisation of bicoid- MT transport via plus and minus ended motors that glue proteins and mRNA in position
What is the purpose of the chorion and vitelline membrane?
Protect the embryo and prevent it from drying out as the VM is hydrophobic
