APS136 2 Flashcards
What is development?
A series of progressive changes in form and function that occurs during an organism’s life
- embryonic stages precede birth, and development continues until death
Fertilisation is..
the fusion of eggs and sperm to produce a zygote
Cleavage is…
the division of cells to form a blastula
Gastrulation is…
the formation of tissue layers and a body axis
Organogenesis is…
the formation of organs
Morphogenesis is…
the mechanism of body shape formation
Fertilisation initiates…
the rapid divisions that produce the multicellular embryo
The cytoplasm and mitochondria of the zygote come from…
the egg
The nucleus of the egg is in the…
animal hemisphere
Nutrients accumulate in the…
vegetal hemisphere
In amphibians sperm enters at the … …; the cortex then rotates exposing the … … opposite
animal hemisphere, gray crescent
Proteins in the gray crescent control…
what form the cells will take
Vegetal cortical cytoplasm is …, whereas animal cortical cytoplasm is …
clear, opaque
Cells typically … in number at each cleavage
double
The line along which cells cleave is called the…
cleavage furrow
The cells in and before the blastula are called…
blastomeres
A blastula is…
a hollow ball of cells (with the hollow centre being called the blastocoel)
In animals, unlike plants, there is very little … during cleavage, so cells get … at each division, and the overall … stays more or less the same
growth, smaller, mass
What are the 3 different types of cleavage patterns? (vary between taxa)
- Complete
- Incomplete-discoidal
- Incomplete-superficial
+ the pattern depends on the amount of yolk and the orientation of spindles
With no yolk, cells are all..
equal in size at cleavage
Yolk … the cleavage furrow, so cells divide …
impedes, asymmmetrically
When there is lots of yolk, the cleavage furrows don’t penetrate the yolk, so cleavage is …. A … forms on top of the yolk in birds.
incomplete, blastodisc (discoidal cleavage)
In insects, … … cleavage occurs. The … migrate to the edge and the … grows inward, partitioning the … into individual …
superficial incomplete, nuclei, membrane. nuclei, cells
- no cytokinesis
What are the 3 ways in which mitotic spindles affect cleavage pattern?
- Radial cleavage - mitotic spindles form at right-angles or parallel to animal-vegetal axis
- Spiral cleavage - mitotic spindles are at oblique angles to animal-vegetal axis
- Rotational cleavage - first division is parallel to a-v axis, second is at right angles
Early in development, cells are…
totipotent
At … the cells’ fate becomes fixed
determination
At … the cells become structurally and functionally specialised
differentiation
What are the three tissue layers?
- Endoderm (inner layer) - digestive tract, circulatory tract and respiratory tract
- Ectoderm (outer layer) - epidermis and nervous system
- Mesoderm (middle layer) - bone, muscle, liver, heart and blood vessels
In sea urchins, the blastula … at the vegetal hemisphere to from a …. Primary and secondary … forms between the endoderm and ectoderm, and an … forms (primitive gut)
invaginates, blastopore, mesenchyme, archenteron
In birds, the blastodisc … will form into the embryo, and the … will form the extraembryonic membranes. Gastrulation in birds starts when … … moves along the blastodisc from the anterior to the posterior, leaving the … … in its wake.
epiblast, hypoblast, Hensen’s node, primitive streak
In mammals, the … forms into the placenta. The inner cell mass contains the …, which becomes the embryo, and the … which becomes the extraembryonic membranes
trophoblast, epiblast, hypoblast
… occurs early in organogenesis and begins the formation of the nervous system in vertebrates
neurulation
The anterior end of the … … develops into the brain
neural tube (forms above the notochord)
Blocks of mesoderm called … produce the vertebrae, ribs, and muscles of the trunk and limbs
somites
… … cells produce peripheral nerves
neural crest
The yolk sac is for…
nutrient transfer
The amniotic sac is for…
protection
The chorion is for…
gas/water exchange
The allantois is for…
waste storage
Development is controlled by…
- the cytoplasm
- genes
- the external environment
Nuclear DNA does 2 things:
- replicates itself
- makes protein (by transcription of RNA) - doesn’t occur in early embryos - transcription isn’t switched on
All enzymes and proteins involved in cell division are provided by…
the cytoplasm
All metabolic cycles and instructions for driving cell division are controlled by…
the cytoplasm
Zygotic cytoplasm comes from the …, so early development is under … control
mother, maternal
… … is the transition from maternal control to embryo control
genomic activation
The timing of genomic activation varies
- In pigs and rats it occurs at the … cell embryo
- In humans and cattle it occurs at the … cell embryo
- In frogs it occurs at the … cell embryo
- 4-8
- 8
- 3,000-4,000
Differentiation results from differential … …
gene expression
Differential gene expression is influenced by…
the cytoplasm and the extracellular environment
What does genomic equivalence mean?
No information is lost in the early stages of embryonic development
In amphibians, cytoplasmic factors in the … … are necessary for development
gray crescent
What are the two mechanisms that give rise to chemical signals involved in development?
- Cytoplasmic segregation - a factor is unequally distributed in the cytoplasm and ends up in some daughter cells but not others (and in different concentrations among cells), causing different differentiation
- Induction - a factor is secreted by some cells to induce others to differentiate
Cells “know” where they are in an animal by interpreting … …. This is given by the concentration gradient of a …
Positional information, morphogen
A signal is considered to be a morphogen if…
- it directly affects target cells
- different concentrations cause different effects
The cells that become the bones and muscles of a limb receive positional information, then organise appropriately. Cells at the base of the bud make a morphogen (…) whose gradient determines the ….-…. … if the limb.
BMP2
Anterior-posterior axis
Highest dose of BMP2 –>
Smallest dose of BMP2 –>
Thumb
Little finger
In mammals, some development genes are active only if they come from a …, others only if they come from an …. This is called … …
Sperm, egg, genetic imprinting
- male-male zygotes don’t produce an embryo
- female-female zygotes don’t form a placenta
Prader-Willi syndrome results from…
a deletion on paternal chromosome 15
Angelman syndrome results from…
a deletion on maternal chromosome 15
… … influence the number, boundaries and polarity of the body segments
Segmentation genes
… … organise large areas along the anterior-posterior axis
Gap genes
… … … divide the embryo into units of two segments each
Pair rule genes
… … … determine segment boundaries
Segment polarity genes
… … are expressed along the length of the body and determine what the segments will become
Homeotic genes
In mice, 4 families of homeotic genes, called … genes, control differentiation along the body axis
Hox
Temporal and spatial expression of hox genes follows the same pattern as their linear order on the…
chromosomes
Antennapedia causes…
legs to grow instead of antennae in drosophila
Bithorax results in…
an extra thorax in drosophila
… is programmed cell death, caused by the activation of “…” genes
apoptosis, death
Human embryos have webbed hands and feet, the enzyme … stimulates apoptosis
caspase
C. elegans has 1,090 somatic cells, … are programmed to die
131
Sometimes an environmental factor is necessary for successful development, for example, house mice raised in microbe-free environments lack … …, and these induce gene expression in the …, which is essential for normal … development
gut bacteria, intestine, capillary
Neurulation is primarily under genetic control, but environmentally derived material in the form of … and … are also needed
vitamins, minerals
Neural tube defects can be reduced if pregnant women receive adequate…
folic acid
In tibet, a lack of … in the diet causes … in adults and … in babies
iodine, hyperthyroidism, cretinism
Environmental factors can also disrupt development. For example, …, found in the corn lily plant, causes birth defects in lambs. It inhibits the action of the … … protein, which is involved in the formation of the neural system
cyclopamine, sonic hedgehog
A clone is…
an individual that is genetically identical to another individual (not necessarily phenotypically identical)
What are the mechanisms of cloning?
- Natural
- Embryo splitting
- Reprogramming somatic cells
- Nuclear transfer
What is the primary mechanism of natural cloning?
Asexual reproduction
Blastomeres in a 2 cell embryo sometimes separate naturally at an early stage, resulting in..
monozygotic twins
Reprogramming somatic cells: sometimes differentiation is …. A carrot root cell can be “tricked” into forming a new plant that is a clone of the original
reversible
Why is somatic cell nuclear transfer (SCNT) controversial?
- The technique is invasive
- There are technical problems
- It gives rise to an ethical dilemma (potential for human to be cloned)
What two features allow cloning by nuclear transfer?
- The nucleus of every somatic cell contains a complete copy of the individual’s genome
- A fertilised egg is totipotent
How is SCNT done?
The DNA (nucleus) from one cell is combined with a fertilised egg that has been enucleated
What were the first sheep cloned by nuclear transfer called?
Megan and Morag (cloned from embryonic cells)
- Dolly was first cloned from adult somatic cells
What was the name of the first transgenic sheep clone?
Polly
- Wilmut and Campbell’s goal was to produce a flock of transgenic sheep that could produce therapeutically useful proteins
What are some potential uses of cloning?
- Developmental research, using clones as controls
- Conservation (e.g. rare or extinct species)
- Cloning of elite livestock
- Disease resistant farming
- Assisted reproductive techniques
- Therapeutic cloning
+ Pharming
+ Xenotransplantation
Clones have … of their own
mutations
Stem cells are … cells that are capable of extensive …
undifferentiated, proliferation
Stem cells produce…
- more stem cells
- differentiated progeny cells
Stem cells in the lab can be induced to differentiate using … …
signal molecules
- e.g. stem cells given vitamin A derivatives form nerve cells
Darwin recognised that relationships among organisms could be deduced from similarities among their …
embryos
Evolutionary Developmental biology (evo devo) looks at..
- How changes in the genes that regulate development affect the adult forms of organisms
- How those genes have changed during the course of evolution
- How these changes have influenced evolution
Many developmental genes are highly …
conserved
- e.g. the same genes drive the development of the fly’s compound eye and the house mouse’s camera-like eye
+ the same set of hox genes provide anterior-posterior information in both mammal and insect embryos
A huge variety of animals are produced by…
a common set of instructions
Morphological changes can result from…
- Mutations in genes that regulate development
- Changes in the spatial expression of developmental genes
- Changes in the temporal expression of developmental genes
… makes all of these pathways of evolution easier
modularity
Development is sensitive to…
environmental and social conditions
In mosquitos, a blood meal stimulates production of vitellogenin, a necessary component of …
eggs
In leafhoppers, gut bacteria are necessary for…
normal abdomen development
The squinting bush brown butterfly has a dry-season and a wet-season with different … …. Temperature during pupation determines … …. This is an example of polyphenism
Wing colouration, adult form
<20 degrees C –> dry season form develops
>24 degrees C –> wet season form develops
(temperature affects expression of distal-less gene - increased expression during wet season)
If spadefoot toad ponds begin to dry up, the tadpoles…
- Develop a wider mouth, powerful jaw muscles and a modified intestine
- Speed up development by eating other tadpoles
