Developmental genetics - lecture 10 Flashcards
What is superficial cleavage in Drosophila?
rapid nuclear divisions without forming separate cells
How are gametes formed in Drosophila?
When some nuclei move to the posterior end
What happens to Drosophila Melanogaster to form the blastoderm?
nuclei move to the edge of the blastoderm , to form syncytial blastoderm . Cell membranes form around cells to create a cellular blastoderm
what does Invagination in Drosophila do, during gastrulation ?
A ventral furrow appears on the ventral surface and cellular movements begin to occur.
Future mesodermal cells move into the middle , this tube will then dissociate to form a layer internally
When does Germ- band occur?
At the same time as gastrulation.
What is Germ- band extension?
Movement of ventral tissue around the posterior end and onto the dorsal side . These cells invaginate in and become the midgut
Forming neuroblasts
After invagination of future mesodermal cells, the ventral furrow closes.
Ectodermal cells move in between external ectoderm and internal mesoderm , forming the neuroblasts
What is a genetic screen?
technique used to identify and study an interesting phenotype within a mutated genotype
Forward genetics
Scientists start the mutation, then determine which genes are involved
what are the three steps involved in forward genetics?
- Generate the mutants
- Identify genes that are mutated
- Find where the genes are expressed
Why is Drosophila well suited to genetic screens?
- Quick generation time
- simple genome
- small and cheap
- easy to determine phenotype
What are homeotic genes?
genes that control body plan axis and growth
▪transcription factors
▪control the pattern of body formation
▪contain a homeobox domain (HOX)
▪activate or repress other genes
Collinearity
The order of expression in the embryo matches the order on the chromosome
What genes control head development in Drosophila
Labial (Lab) and Deformed (Dfd)
What genes control thorax development?
- sex combs reduced (SCR)
- Antennapedia (Antp)
- Ultrabithorax (Ubx)
What genes control abdomen development?
- Abdominal A (abdA)
- Abdominal B (Abd B)
Who won Nobel prize in 1995 for discoveries concerning early embryonic
Eric Wiecschaus and Christiane Nusslein - Volhard?
What gives the antennae in the head?
Labial and Deformed give antennae
What gene give the legs in the thoracic segment 1?
Sex combs reduced
What gene gives legs and wings in thoracic segment 2?
Antennapedia
What genes gives a pair of legs and halteres in thoracic segment 3?
Ultrabithorax and antennapedia
What genes give no outgrowth in abdominal segment 4
UbaA Ubx and Antp
What is syncytial blastoderm?
all the cleavage nuclei are contained within a common cytoplasm.
What is the common form of Drosophila melanogaster?
- 1 pair of wings
- halteres
- 3 pairs of legs
How do you generate mutants in forward genetics?
- male mutated
- Breed coproduce F1; producing some mutated animals and some normal
- F1 offspring mutated with more wild animals to produce F2 . Then F3.
- only 1/16 of the offspring will be homozygous recessive and therefore be mutated
What begins gastrulation?
Appearance of a ventral furrow , then cellular movements can begin
