What is meant by the cleavage of an embryo?
the pattern of early mitotic divisions that divides up the large volume egg cytoplasm
the early zygote is uniquely large and with each division the cells get smaller –> this stops at the mid-blastula transition
What is the mid-blastula transition?
the point where the blastula changes from the cleavage stage of development to gastrulation
Which of the big 7 (sponges and cnidaria not included) are deuterostomes and which are protostomes?
deuterostomes: Chordata, echinoderms
protostomes: Nematoda, annelids, Mollusca, Arthropoda, platyhelminthes
Key features of protostomes
- gastrulation becomes the mouth
- determinate cleavage meaning if you take a cell away you will not have a viable embryo
- spiral cleavage
Keu features of deuterostomes
- gastrulation becomes the anus
- indeterminate cleavage meaning if one cell is damaged it still has the ability to become a whole embryo
- radial cleavage
Key features of an embryo
ectoderm - will form epidermal layer of skin
endoderm - will form the lining of the gut, liver and lungs
mesoderm - will form muscle, bone, kidney etc
animal pole - cytoplasm more active and contains nucleus
vegetal pole - cytoplasm less active and contains most yolk
What is a blastopore?
the temporary opening on the surface of an early embryo (gastrula)
What separates animals having a direct development compared to an indirect development?
if the animal has lots of yolk or a placenta then it is direct e.g. human. if it has little yolk then it is indirect e.g. mosquitos
What is a coelom
a fluid filled body cavity between the body wall and the digestive tract
- provides space for internal organs
- help organ development
- acts as a cushion to protect organs
What is the evolutionary significance of the coelom?
- facilitates advanced organ development
- enables more complex body segmentation
- offers evolutionary advantages e.g. greater mobility
What is an acoelomate?
doesn’t have a coelom e.g. flatworms
What is an pseudocoelomate?
incomplete or false coelom e.g. roundworms
What is an coelomate?
have true coeloms lined with mesoderm e.g. humans and earthworms
Explain the different mesoderm formations
- schizocoels: mesoderm cells fill blastocoel to form a band around gut –> spaces open in the band to form the coelom. protostomes
- enterocoeles: cells from the gut lining grow pouches into the blastocoel and pinch off. deuterostomes
What is cell differentiation?
development of non-specialised cells into cells with specialised functions
controlled by gene expression
What is gene expression and what controls it?
activation of a gene that results in a polypeptide or protein
controlled by transcription factors
What are homeotic genes?
regulatory genes that code for transcription factors
determine where certain anatomical structures will develop during morphogenesis and organogenesis
What is the homeobox genes?
coding sequence within homeotic genes (also shortened to HOX genes)
number and arrangement varies among different animals but all animals have them
Key features of echinoderm development
- evolved from bilateral animals
- develop into bilateral larvae
- during development part of the larvae is discarded to produce a pentaradial adult
