early development

Question 1

what is a metazoan

Answer 1

a multicellular animal which goes through the stages of embryonic development

Question 2

what is cleavage

Answer 2

the first divisions of a zygote where blastomeres form but there is no net growth of the embryo

Question 3

what is the mid-blastula stage

Answer 3

the point at which zygotic DNA transcription begins- up until then the divisions are caused solely by maternal molecules and therefore can in theory reach this point with no nucleus

Question 4

what is fate mapping

Answer 4

is allows the determination of which parts of the organism develop from which parts of the embryo. this can be done through injection of dye or through transplant (produces chimeric organisms)

Question 5

what is gastrulation

Answer 5

the invagination of the blastula where the three germ layers develop- the ectoderm, mesoderm and endoderm

Question 6

what is neurulation

Answer 6

the development of the nervous system, including the notochord, primitive brain and neural tube

Question 7

what is the pharyngula bottleneck

Answer 7

embryos of different species converge to a similar form in the pharyngula phase, after which they dramatically diverge

Question 8

why are embryos important in phylogeny

Answer 8

phylogeny is often more accurately assumed in embryos than adults eg sea squirt embryos have a notochord, identifying it as a chordate

Question 9

what are the groups within bilateria

Answer 9

bilateria (or triploblasts) are divided into deuterostomes (anus first) and protostomes (mouth first). the ancestor to bilaterians was protostome- like

Question 10

describe BNP and chordin

Answer 10

in chordates BNP acts ventrally and chordin acts dorsally- this is flipped from other deuterostomes and conserved protosomes