Development Flashcards
Sexual reproduction
● Haploid sperm meets haploid egg
↳diploid Zygote
● Diploid stage dominates life cycle
Zygote undergoes Cleavage (Cleavage causes cell division without cell growth, i.e. not changing the overall size of the embryo, like splitting a party balloon into sections)
↳Blastula (hollow ball) The hollow ball forms an invagination (like a pouch)
that sets up the tissue layers that will ultimately
form the adult body parts.
● Blastula undergoes Gastrulation
↳Gastrula
Exceptions to sexual
reproduction
● Fragmentation (e.g.
planarians, sea stars)
● Parthenogenesis (e.g. aphid giving birth to live young via unfertilised egg)
Ectoderm, Endoderm, Mesoderm
● Ectoderm – surface of embryo, outer animal layer
● Endoderm – lines developing digestive tract
● Mesoderm – between Ectoderm and Endoderm
Diploblastic and Triploblastic
Diploblastic
2 germ layers e.g. jelly fish
Triploblastic
3 germ layers e.g. all bilateral Animals
Body cavity (coelom - hollow cavity)
Fluid/air filled space between digestive tract and outer wall
Function -
Cushioning of organs, Allows organs to grow and
move, Act as hydrostatic skeleton
Acoelomates,Pseudocoelomates, Coelomates - body cavity
- Acoelomates – no body cavity at all e.g. flatworms
- Pseudocoelomates – formed when mesoderm only partially enters the blastocoel, e.g. nematodes
- Coelomates – formed from tissue derived
from mesoderm e.g. earthworm
Axes of symmetry
● None (sponges)
● Radial – no left or right, no front or back
● Bilateral – 2 axis of orientation front to back & left and right
Animal Body Plans
A body plan is “an assemblage of morphological and developmental features shared among a group of animals” typically featuring:
● Symmetry
● Embryonic tissue layers
● Body cavities (also segmentation, appendage disposition…)
Cambrian explosion
Most animal body plans were established during the cambrian explosion
Cambrian explosion c. 539 Ma - a period of just 13-25 million years when
almost all complex animal life appears in the fossil record
Avalon explosion
Avalon explosion c. 575 Ma – a pre-cambrian event that might have established more
complex animals than previously thought
Main differences between Protostome Annelids,
Hexapods, Crustaceans &
Molluscs
Deuterostome Echinoderms
& Chordates
● Cleavage type
● Coelom formation
● Fate of the Blastopore
Protostomes - cleavage
In protostomes, when cleaving from 4-cells to 8-cells, the cells twist. This carries on in further cell divisions to create a spiral-shaped embryo
They also have determinate cleavage, meaning each cell’s fate to become different tissue types is pre-determined
Deutrostomes - cleavage
In deuterostomes they have radial cleavage, so do not spiral. Each cell’s fate is also indeterminate, meaning any cell has the capacity to become any other future
tissue type. This means that identical twins are possible in deuterostomes
Protostomes - coelom
In protostomes the coelom is formed inside the
mesoderm from the outset, as a pouch from the archenteron
Deuterostomes - coelom
In deuterostomes the coelom forms through folds in the archenteron
Blastophore
The blastopore is that first invagination that forms in the blastula when it goes through gastrulation
It’s the fate of this hole that gives rise to the names of these two groups, either forming the mouth or anus
Homeotic Transformations
When one body part grows in the wrong place this is called a homeotic transformation, these have been a focus of research because you can easily look for mutants in wild or artificially mutated populations
Hox genes
Regulatory genes that
tell the developing embryo where to form different limbs/organs (but not
how to form them)
Hox genes (and other regulatory genes) all contain the same short of
DNA sequences called Homeoboxes
What are the genes controlling developmental pathways and networks
They are highly
conserved in bilateria
Pax 6*
Hox*
Brachyury
Distalless*
BMP4/Chordin
Direct Development
The juvenile form largely
resembles the adult form
Indirect development
The animal’s
juvenile stages are morphologically
distinct from the adult, with sometimes multiple transient stages of maturation e.g. typical insect life cycle involves:
egg→ larva→ pupa→ adult
The animal kingdom is a
monophyletic clade called …
Metazoa
Most phyla belong to …
Bilateria
Ecdysozoa
includes
arthropods, nematodes +
other phyla, they typically:
● Excrete exoskeleton
● Undergo moult
Lophorophozoa
Includes annelids, molluscs and many other phyla.
They either:
● Develop a lophophore (crown ciliated tentacles involved in feeding (e.g. Brachiopods & ectoprocts), OR
● Have a distinctive development stage called Trochophore larva (e.g. molluscs & annelids)
