cleavage Flashcards
what are the stages from first cleavage to implantation
1/ Mitosis & organised cell division (cleavage)
2/ compaction - start of cell polarisation
3/ lineage formation (icm and te)
4/ formation of functional epithelium (needed for blastocyst formation)
5/ hatching from zona pellucida
6/ attachment and implantation into uterine wall
what is a blastomere
each of the identical cells formed by a cleavage division
mammalian cleavage occurs via ________________
…via contractile rings
why is cleavage so important
1/ generation of a large number of cells
2/ increase in nucleus to cytoplasmic ratio (optimal for RNA/ protein production to allow differentiation)
the length of the G1 and G2 phases is _____% of normal somatic cells
20% -significantly reduced
what do the number and type of divisions depend on
the size of the zygote - governed by the amount of nutrients held in the yolk
mammals show what type of cleavage
(rotational) holoblastic cleavage - complete division of whole cell
what type of cleavage is observed in fish reptiles and birds
meroblastic cleavage - incomplete division
what determines the pattern of cleavage
the orientation of the spindle
- the plane of cleavage is always perpendicular to the spindle
what are the four types of complete holoblastic cleavage
Radial
Spiral
Bilateral
Rotational
in mammals the first cleavage is _____________ and the second cleavage is _____________
the 1st is meridional, the 2nd is rotational
when is the gamete epigenetic pattern lost and the pluripotent pattern seen
8-16 cells
