Genetics of Development
All Cells in an Organism Contain the Same DNA Come from the same zygote dividing over and over again
Cells Are Different Because they Express Different Genes Each cell generates different proteins and at different times Very complicated, focus of research currently
Homeotic/Hox Genes Control developmental patterns and sequences Determine where each body part develops
Very Well Conserved in Animals We have almost the same exact Hox genes as fruit flies But we have more copies due to gene duplication
What do Hox genes do? Code for transcription factors Turn on or off combinations of genes in different regions of the embryo
Emma…
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Embryonic Induction Cells stimulate nearby cells to express certain genes E.g. as the eye forms, one cell causes others to express the genes necessary to make eye cells Transplantation experiments showed adding one cell could change cells around it
How Induction Works One cell specializes, likely due to Hox genes It triggers further development of nearby cells Likely produces proteins that act on the genes of nearby cells Ensures proper timing and development
Spemann-Mangold Experiment
All Cells Originally Can Be Anything But over time processes restrict what genes can be expressed DNA methylation and other processes shut off many genes Processes like induction shut off gene expression or turn on gene expression long-term. When new cells form they usually have the same genes shut off as their parent cell
MicroRNAs Regulatory molecule that blocks translation of RNA Controls development and cellular organization
MicroRNAs Appear to help fine- tune development Prevent certain genes from being expressed in certain cells
Apoptosis As organisms grow, some cells must be destroyed Apoptosis= programmed cell death E.g. originally there are cells between your fingers- they die, separating the fingers
Other Examples of Apoptosis Destruction of WBCs that attack the body Destruction of neurons that are not used (pruning) Destruction of mutated cells Recycling of mature cells 50-70 billion cells apoptosize each day