Developmental Biology Flashcards
Embryogenesis
process that makes a single-celled zygote into a multicellular embryo
What happens after fertilization?
cleavage
cleavage
rapid cell division without any growth between division events
Blastula
when cleavage is complete, the embryo consists of a mass of blastomere cells with an inner cavity known as the blastocoel
Potency of blastomere cells
multipotent
can develop into more than one cell type
Monozygotic twins
come from the same zygote, but their blastomeres are separated in an early stage
fertilized by the same sperm
Dizygotic twins
occur from two independent fertilization events
fertliized by two different sperms
Gastrulation
extensive and highly organized movements that radically rearrange the embryonic cells into a structure called gastrula
When does gastrulation begin?
with the formation of an opening called a blastopore
cells move towards the blastopore to form a tube-like structure (the gut)
Germ layers
created during gastrulation
known as ectoderm, mesoderm, and endoderm
Ectoderm
ectoderm cells on the surface of the gastrula will give rise to the entire nervous system
How do cells know how to specialize?
through communication
stem cells
able to self renew (copy themselves) or differentiate
totipotent
potency
developmental potential (ability to become other cell types)
totipotent
can give rise to all lineages (including placenta)
pluripotent
can give rise to all cell types of the body
multipotent
can develop into more than one cell type
unipotent
can only produce one type of cell
Morphogens
mRNA molecules that help establish the basic anterior/posterior coordinates
pattern formation molecules that are present in a concentration gradient
Bicoid
a type of morphogen that develops anterior structures
Maternal effect genes
genes transcribed in the ovarian (“nurse”) cells that surround the developing egg
morphogens are an example
How does Bicoid work?
it is a regulatory transcription factor that activates many genes when turned on
nanos
an RNA binding protein that helps to develop the posterior coordinate
affects translation, whereas Bicoid affects transcription
Bicoid and nanos
are present in opposing concentration gradients
this allows one end to develop anterior structures and the oppossing end to develop posterior structure
Stages of development/genes
early in development gap genes define general position of head, thorax, and abodominal region
later, pair-rule genes define the edges of individual segments
finally, homeotic genes are expressed along the length of the body and tell the segments what to become
Homeotic/hox genes
determine that one part of an animal will be morphologically distinct from another
Hox genes code for transcription factors
Homeobox
a DNA sequence that is required for the expression of hox genes
encodes for the homeodomain, which binds consensus DNA sequences in the promoters of many downstream, target genes
homeobox sets into motion a series of events
Homeotic transformation
the development of a dramatic mutation in invertebrates where a structure is located in the wrong place
Why do we not see homeosis in vertebrates?
we have 4 families of Hox genes, while invertebrates only have 2, so it makes it harder to mutate
What are the four families of Hox genes considered?
paralogus
have a similar DNA sequence and A/P position
What happens if there are no Hox genes?
there is no variation in morphology
What is something that vertebrates have that invertebrates do not have when it comes to Hox genes?
Retinoic acid
Communicates what Hox genes are going to be expressed where
Exists in a concentration gradient
Lack of retinoic acid can lead to extreme birth defects
