1. Timing and Development of Growth

2. All Cells in an Organism Contain the Same DNA
Come from the same zygote dividing over and over again

3. DNA Review 1 molecule of DNA forms a chromosome
Each chromosome contains many segments of DNA called a gene
1 gene codes for one polypeptide (portion of a protein)
Only about 1% of the DNA consists of genes

4. Gene Expression DNA in the nucleus is transcribed into RNA
RNA exits the nucleus and is translated into a polypeptide by ribosomes

5. Control of Transcription
The enzyme that transcribes DNA (RNA Polymerase) requires transcription factors
Activation of transcription factors triggers transcription, thus expressing the gene

6. Cells Are Different Because they Express Different Genes
Each cell generates different proteins and at different times
Very complicated, focus of research currently

7. During Development Different Genes Are Expressed
Homeotic genes control developmental patterns and sequences
Determine where each body part develops
Messing with homeotic changes researchers have gotten legs to grow instead of antennae in flies
Well conserved

9. Embryonic Induction
As cells develop and mature, they cause other cells to express certain genes
I.e. as the eye forms, one cell causes others to express the genes necessary to make eye cells
Allows each cell to develop at the correct time

12. 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.
When new cells form they usually have the same genes shut off as their parent cell

13. Genetic Mutations and Development
Minor mutations in homeotic genes or others can have hugely detrimental effects on development

14. MicroRNAs Regulatory molecule that blocks translation of RNA
Controls development and cellular organization

15. Apoptosis As organisms grow, some cells must be destroyed
Apoptosis= programmed cell death
I.e. originally there are cells between your fingers- they die, separating the fingers

16. Growth of Plant Seeds
Usually triggered by warm temperatures and availability of water
Evolved so that plants begin growing in spring- when light and water are available

17. Other Triggers Extreme heat / fire Long periods of cold
Digestive enzymes
All ensure growth at appropriate time