BIOL10002 Lecture Notes - Lecture 31: Gastrointestinal Tract, Invagination, Dynein
Lecture 31
Development Part 2
Inheritance
DNA and mitochondria come from the mother, DNA and centriole comes from the father
Non-mammalian oocytes
have an animal pole and a vegetal pole, which means after the second division the cells are not
identical
2 lineages that will have different developmental outcomes
Heavy cytoplasmic components sink to the bottom which is important for developing polarity
vegetal pole divides slower than the animal pole
The grey crescent – not in mammals!
sperm attaches to oocyte and as a result bilateral symmetry is created by an anterior-posterior
axis.
β-catenin and GSK-3 (glycogen synthase kinase – phosphorylates β-catenin and targets it for
degradation) are in the eggs cytoplasm, and after sperm entry a GSK-3 inhibitor moves from the
vegetal cortex into the grey crescent, where it prevents degradation of β-catenin
as a result there is more β-catenin on the dorsal side and more GSK-3 on the ventral side
Types of cleavage
holoblastic (complete or total), or mesoblastic (partial)
Complete cleavage – eggs with little yolk. Cleaves evenly.
Incomplete cleavage – lots of yolk. Cleave furrows do not fully penetrate.
- Superficial cleavage - a variation of incomplete cleavage, where the plasma membrane grows
inward around nuclei and forms cellular blastoderms. Repeated mitosis without cytokinesis (multiple
nuclei in the endoplasm). Nuclei move towards the yolk free periplasm. Pole cells form at posterior
pole
- Discoidal - embryo forms as a blastodisc that sits on top of the yolk.
Mammals: holoblastic and rotational. First cell division parallel to the animal–vegetal axis. second
division
Cleavage results in egg becoming a regular sized cell (downsizes)
Stages of development
1. Blastulation
- A blastomere is a cell formed after first cleavage of a fertilised ovum: blastomeres make up a
blastocyst
- they become determined— committed to specific fates—at different times in different species.
- In mosaic development cells are already determined, so if one blastomere is removed, a portion
of the embryo will not form
- only cells that divide with part of the grey crescent will develop normally - polarity will be
equivalent
- In regulative development other cells compensate for any lost cells – includes humans
32-cell stage: Inner cell mass (will form embryo) and Trophoblast (cells secrete fluid to create the
blastocoel cavity) – as this stage the cell is called a blastocyst
Fraternal twins = 2 eggs, Identical twins = inner cell mass splits
2. Gastrulation
Transformation of the blastula/blastocyst into an embryo with multiple tissue layers and a body axis.
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Dna and mitochondria come from the mother, dna and centriole comes from the father. Have an animal pole and a vegetal pole, which means after the second division the cells are not identical. 2 lineages that will have different developmental outcomes. Heavy cytoplasmic components sink to the bottom which is important for developing polarity. Vegetal pole divides slower than the animal pole. Sperm attaches to oocyte and as a result bilateral symmetry is created by an anterior-posterior axis. As a result there is more -catenin on the dorsal side and more gsk-3 on the ventral side. Types of cleavage holoblastic (complete or total), or mesoblastic (partial) Complete cleavage eggs with little yolk. Superficial cleavage - a variation of incomplete cleavage, where the plasma membrane grows inward around nuclei and forms cellular blastoderms. Repeated mitosis without cytokinesis (multiple nuclei in the endoplasm). Discoidal - embryo forms as a blastodisc that sits on top of the yolk.
