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L18- development of multicellular organisms
Karten in diesem Stapel (9)
- 1Development from a single cell to many different cells and organs- All life starts off as an egg (zygote)
- Once fertilised, the egg cell makes many cells through multiple rounds of cell division.
1. Fertilisation: 1 sperm enters the egg and releases nuclear contents (genetic material) within. This sets off a chemical reaction, a wave of calcium across the egg, making it impermeable to other sperm.
Divides, forming a zygote
2. Zygote then moves from the oviduct, where cell divisions begin, and by the time it reaches the uterus, where it implants, it is a blastocyst. - 2Proliferation and differentiation- During embryogenesis the organism gets bigger (proliferation), and more complex (differentiation).
- all cells in the organism contain the same genetic information, although they make up a number of different cell types with different shapes and functions.
- in order to differentiate, cells must be equipped with different proteins. These are encoded by genes, so, in order to differentiate, cells must express different genes. - 3Proliferation-Fertilisation
-Cleavage (1st rounds of division)
-Blastula (hollowed embryo)
-Gastrulation (formation of germ layers) - 4How cell layers become tissue and organs: Gastrulation- gastrulation is the reorganisation of the blastula into a 3 layered embryo
Germ layers:
*Ectoderm: goes around the outside, forms skin and neural tube
*Mesoderm: Layer under the ectoderm, forms muscle, bones and some organs
*Endoderm: inside layer. Forms digestive trancts and respiritory system
- each step of differentiation is built upon the previous step, becoming more specialised as you go along - 5Pattern formation: How shapes and form emerge during development- Patterns are generated early on a small scale, ranging from just 10s to a few 100s of cells.
- Adult pattern is due to the growth of the basic pattern
- Key events in human development occure during the earliest stages of embrogenesis: germ layers differentiating, pattern laid down, further growth.
- However, development can go wrong in a number of ways as the process is so long and complex. - 6How genes control development- to understand how genes control development, model organisms can be used, as many genes are conserved between organisms.
EG:
- fly
- zebra fish
- frog
- chick
- mouse - 7Experiments investigating development in the frog (xenopus)- synchronised developent in frogsspawn; many frog eggs divide at the same time.
- eggs are outside the body so stages of development can be easily studied - 8Investigating how genes regulate development in a frog- Pax-6: transcription factor expressed at the regions of the embryo where the eye is going to form
- Finding out where the genes are expressed gives an idea as to what they do in development.
- hypothesese can be tested by overexpressing genes of interest into specific areas. Adding RNA for the gene in an area that is not usually expressed.
- this is done using a whole-mount in situ, where a lineage tracer shows where RNA has been injected.
However, the way we can prove this, inhibiting PAX-6 must result in no eye devlopment, which it did. - 9Results of mutations of the PAX-6 gene in humans- no iris forms so light cannot be controlled
- photophobia
- issues with optic nerves
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- cell bio l18 development of multicellular organisms
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- Rose P
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