Cleavage Flashcards
Fertilization is followed by _____, a period of rapid cell division without growth.
cleavage
What is the end result of cleavage? (2)
o Cleavage partitions the cytoplasm of one large cell into many smaller cells called blastomeres.
o The blastula is the resulting ball of cells with a fluid-filled cavity.
o The fluid-filled cavity is called a blastocoel.
What happens in terms of cleavage in eggs with little yolk? (3)
o In species whose eggs have little yolk; such as Sea Urchins and mammals; cleavage occurs throughout the whole egg.
o This pattern is termed Holoblastic cleavage- which is a complete division of the egg
o It results in cells of equal size surrounding the blastocoel.
Organisms such as the frog and other amphibians have a _____ yolk
moderate
What does the yolk in species with moderate yolk result in?
The yolk in these species slows down cell division and result in the formation of blastocoel on the Animal pole.
The egg yolk affects cleavage patterns and results in polarity - defined by the distribution of yolk:
o Vegetal pole has more yolk.
o Animal pole has less yolk.
What does the egg’s polarity result in?
The polarity also causes unequal cell divisions which result in the blastocoel forming entirely in the animal hemisphere.
The egg’s polarity and ____ ____ influence the establishment of the body axis following sperm binding.
cortical rotations
What are cortical rotations?
Cortical rotations is the movement of the egg’s cytoplasm towards the point of sperm entry to reveal the grey scent.
The animal – vegetal poles dictate _____-_____ axis
anterior-posterior
What do cortical rotations dictate?
Cortical rotations dictate where the dorsal-ventral axis will form
What pattern does the first cleavage plane follow? (2)
o The first cleavage plane usually follows a pattern that bisects the zygote’s animal and vegetal poles.
o Once the anterior-posterior and dorsal-ventral axis are established, the right and left axis is fixed.
What happens in cleavage in eggs with a large yolk? (3)
o In eggs of birds and other reptiles, the cleavage furrow cannot pass through the yolk
o This is called meroblastic cleavage - incomplete division.
o This type of division produces a disc of cells with two layers on top of the yolk mass called a blastoderm.
o In chicks, _____ plays a role in the establishment of the anterior-posterior axis.
o __ levels between the two sides of the blastoderm establish the dorsal-ventral axis.
gravity
pH
Cell cycle during cleavage-stage
Cell cycle after cleavage stage
