tim boswell2 Flashcards
how many segments does an adult drosophila have
12; 1 head, 3thorax and 8 abdomen
what are imaginal discs
clumps of of undifferentiated epithelial cells in the larva that become new adult strctures like mouthparts, legs , wings etc
does moving an imaginal disc still give rise to the structure its sopposed to
most of the time.
sometimes it doesnt; transdetermination
what is a homeotic mutant. give an example
an organism with homeosis (transformation of one body part to another)
antennapedia; legs for antenna
which chromosome are drosophila homeotic genes on
3
how many complexes of homeotic genes are there? what are these clusters known as collectively? name them? how did different complexed evolve
2
antennapedia complex; expressed anteriorly (head)
bithorax complex;expressed posteriorly (abdomen)
HOM-C complex
different complexed evolved by duplication
what sequence do all homeotic genes contain? how many bp’s is it? how big it the protein it is expressed as
homeobox sequence, 180bp, 60AA protein called the homeodomain
how to homeotic genes have their effect on body plan
they are expressed as transcription factors which bind to DNA and activate gene’s whos products will have developmental functions. Reaper, the apoptosis gene is activated
what is a hox gene
a gene with the 180 bp homeobox sequence, and is part of the HOM-C complex
what evidence is there for hox genes having their effects on segments
knocking out individual hox genes lead to deformaties in different segments
what are the 4 hypothesis why for different body plans exist
1) changes in the number of hox genes
2) different body zones express different genes
3) genes are expressed in all zone, but local acitvity ushc as inhibition occours
4) target genes respond differently to hox gene TF’s
discuss the steps in amphibian gastrulation
1) endoderm cells become bottle cells and move inwards, creating a dorsal lip of the blastopore
2) epiboly occours; ectoderm spreads out from animal pole, covering all of the embryo apart from the yolk plug
3) mesoderm move past dorsal lipdand spread out under the ectoderm
4) endoderm move inwards past dorsal lip and spread out underneath the mesoderm
5) the archenteron expands (eventually becomes gut) as the blastocoel is destroyed
discuss amphibian neuralation (follows gastrulation)
1) the dorsal mesoderm clumps together to fom the notochord (forms spinal column) and somites (form muscle, skin, vertebrae)
2) the cells above the dorsal mesoderm go on to become the nervous tissue (brain, spinal cord) and are therefore sometimes called the neurectoderm)
describe how the dorsal mesoderm become the notochord
the cell layer thickens into a neural plate before becoming tube like (neural groove) and then a full neural tube
define primary embryonic induction
the process by which mesoderm specifies the fate of overlying neurectoderm
