Ch. 21 The Genetic Basis Of Development

Eye on antennae

I. Embryonic development A. Three processes make embryo development possible. Cell division - this would only produce identical cells Cell differentiation - cells become specialized in structure and function Morphogenesis - "creation of form" the physical process that gives an organism shape(this is like Power Rangers).

B. All three process overlap 1. Morphogenesis allows for the basic body plan. Cell division and cell differentiation help to direct morphogenesis. 2. Animals and plants have different morphogenesis Animals complete morphogenesis during embryonic development, and only grow for a certain juvenile period Plants have areas in which growth occurs throughout the life of the plant called meristems - perpetual embryonic regions. These occur at the tips of shoots and roots.

C. Model organisms used to study development 1. Frogs –They have large eggs that are easy to see –Fertilization and development happen outside the body. 2. Drosophila, C.elegans, mouse, zebra fish (Decker has some of these) and for plants Arabidopsis. 3. Drosophila has a 2 week generation time 4.Caenorhabditis elegans can be grown easily in petri dishes and grows from zygote to adult in 3.5 days. Its genome has been sequenced. They are also hermaphrodites

Mus musculus - mouse, there are now transgenic mice and mice who have had genes mutated, however embryo development is difficult to see. Danio rerio - zebrafish - easy to breed and generation time is longer than other models (2-4 months) but early development is quick with a fish hatching two days after fertilization. Arabdopsis thaliana - a weed can produce 1000s of progeny in 8-10 weeks. They are easily transformed

Differential gene expression - we know that all cells have the same genes so how do certain genes get turned on and others not? –Carrot cells taken from the root grew into normal carrot plants (a clone). Plant cells are totipotent- they have the potential to become any type of cell. –Animal cells do not behave like this. Many can not even divide in culture at all. Attempts have been made to remove the nuclei from a frog egg cell and replace it with the nuclei from various stage tadpole cells. This has been marginally successful.

As embryonic development progresses potency of cells in animals changes. –Dolly - The nucleus from an udder cell into a unfertilized egg cell ( the udder cells were stopped at the G1 checkpoint), then the eggs were implanted into surrogates. Her mitochondrial DNA is from the egg donor. –Many clones do not develop normally because of DNA being methylated in the wrong places and disrupting gene expression.

Stem cells- unspecialized, continually reproducing, can differentiate into specialized cells of different types. –Bone marrow- stem cells for different blood cells –Recently discovered brain stem cells –Pluripotent- cells that can become different types of cells. –Embryos have stem cells that can be made immortal.

Stem cell,Stem cell, Brain stem cellBrain stem cell

Different cell types make different proteins –Specific cells make proteins that will direct their specific roles in the body. –Cytoplasmic determinants from the mother direct the embryo development –3. Induction - signal molecules cause changes in developing cells by causing changes in gene expression.

Transcription factors

Apoptosis

Evolution of homologous genes

Mice