Lecturea 2-4 Flashcards
how does a new multi cellular organism arise
an aggregation of many single cells.
cellular slime molds
these form multicellular aggregates in which cells are separated by their membranes
example of cellular slime mold
dictyostelium discoideum
fruiting body
fungal structures that contiain spores
asexula reproduction
bacteria and simple animals such as hydra can reproduce by budding.
mechanisms of asexual reproduction
fission - (separation of an organism into two or more individuals of approx equal size)
fission
fission - (separation of an organism into two or more individuals of approx equal size)
budding
budding - new individuals arise from existing ones. (found only in invertebrates0
fragmentation
two step process, breaking of the body into pieces, all or some of which develop into adults, followed by regeneration. (regrowth of lost body parts (annelid worms)
parthenogenesis
females produce offspring from unfertilised eggs (mainly invertebrates )
bees wasps and ants
zygote
a fertilised egg cell
driving force behind evolution
variation
general principles of development
cell division, cell differentiation, morphogenesis
gametogenesis
Spermatogenesis- the production of mature sperm is a continuous process in the adult
male. Sperm structure is very consistent throughout the animal kingdom.
Oogenesis, the development of a mature egg, is a prolonged process
why dont we study development in humans
Observation is difficult
• Morally and ethically- no experiments on human embryos (following implantation).
• We wouldn’t want to (nor could we) breed humans to look at effects of gene mutations
on embryos.
R
model organism
an organism who has very similar developmental mechanisms to the organism being studied
aspects to be considered when choosing a model organism
- biological considerations
- practical considerations
- historical considerations
organism for observing development and morphological analysis
Advantages in this case would be large eggs, accessible embryos, short development time, and easy to keep in the lab. So the organisms of choice for this kind of work would be the amphibian (frog) and the chicken. Arabidopsis in the case of plants.
for manipulating the embryo (experimental biology)
larg accesible embryos, robust embryos that can tolerate manipulation.
can be grown in a dish, in culture.
frog or chick
vertebrate
The frog Xenopus laevis (Chp 46 – first page)
Advantages
•Ease of access and manipulation of the egg and embryo
allowing experimental manipulation, assay inductive interactions
•Robust embryos, can tolerate manipulation in relatively simple lab facilities.
•Parts of the embryo can easily be cultured.
•Rapid development, 4 days to a free swimming tadpole.
•A well-established system
Disadvantages
•No genetics. Complex, uncharacterised genome.
•Animals cannot be bred for multiple generations in the lab.
The mouse Mus musculus has a long history as a mammalian model of development.
Advantages
•Much is known about its biology, including its genes.
•The genome is well characterized and almost completely sequenced
•Sophisticated and elaborate techniques exist to manipulate mouse genes:
transgenic mice and
mice in which particular genes are “knocked out” by mutation.
Disadvantages:
Mice are complex animals with a genome as large as ours, and their embryos develop in the
BYU11102 Organisms to Ecosystems: Multicellularity and Development
Dr. Rebecca Rolfe – Lecture 2
mother’s uterus, hidden from view.
•The embryo develops in utero and is inaccessible.
-we are restricted to snap shots of development
•Embryo culture is difficult and limited.
•The generation interval is long (3 months)
•Difficult to find genes by mutational screens, because of the above.
But the mouse is still an important model system because we want to be able to study
development in a mammal. It serves as a good model for human development.
invertebrate
INVERTEBRATE
The nematode worm Caenorhabditis elegans normally lives in the soil but is easily
grown in petri dishes.
•Only a millimeter long, it has a simple, transparent body with only a few cell types and
grows from zygote to mature adult in only three and a half days.
•Its genome has been sequenced.
•It is easy to identify mutant animals: Because individuals are hermaphrodites, it is easy to
detect recessive mutations: Self-fertilization of heterozygotes will produce some homozygous
recessive offspring with mutant phenotypes.
•The huge advantage is its simplicity: every adult C. elegans has exactly (only) 959 somatic
cells. These arise from the zygote in virtually the same way for every individual.
•By following all cell divisions with a microscope, biologists have constructed the
organism’s complete cell lineage, a type of fate map.
A fate map traces the development of an embryo – Cell lineage analysis. (
For Developmental genetics:
Advantages would be ease of breeding in the laboratory, short generation interval (time
from fertilisation to sexual maturity), simple or small genome and ease of observing embryos
to see mutant effects. Organisms that have been widely used for this are the fruit fly
(Drosophila), the zebrafish (Danio), the nematode worm (Caenorhabditis elegans), The plant
Arabidopsis thaliana, the mouse (despite major disadvantages, see below).
transcription factors
In molecular biology, a transcription factor is a protein that controls the rate of transcription of genetic information from DNA to messenger RNA, by binding to a specific DNA sequence
actin and myosin
In summary, myosin is a motor protein most notably involved in muscle contraction. Actin is a spherical protein that forms filaments, which are involved in muscle contraction and other important cellular processes
