Chapter 20: Developmental genetics

What does development mean?

a series of changes in the state of a cell, tissue, organ, or organism

What does developmental genetics mean?

how gene expression controls this process

What is the most helpful model organism?

Fruit fly

What happens during development?

Each cell receives positional information that tells it where to go and what to become

What happens when cells receive positional information?

4 things that the cell can do:

• divide, migrate, differentiate, or die

Development of hand

1. Cell division promotes the growth of the limb

2. Cell migration causes cells to reach their correct location.

3. Cell differentiation produces specialized cells such as muscle cells.

4. Apoptosis eliminates cells in between the fingers

How is this positional information provided?

by morphogens and cell adhesion molecules

What are morphogens?

signaling molecules during development

• substances that govern the pattern of tissue development

Are morphogens distributed symmetrically or asymmetrically?

Asymmetrically

How are morphogens distributed?

• in the oocyte or egg precursor

• In the embryo by secretion and transport

How do morphogens act?

Act in a concentrated dependent manner with a critical threshold concentration

• Give positional information and promote cellular changes.

What does anterior end mean?

head side

What does posterior mean?

tail side

What does Dorso mean?

back side

What are the cell adhesion molecules responsible for?

cell stickiness

How does cell adhesion provide positional information?

like adhesion molecules come together. (cell sorting)

Case Study: Development of Drosophila (Fruit fly)

What is phase one?

establishment of body axes

How are body axes determined?

based on the concentration of morphogens (ex: Bicoid tsc factor)

• morphogens are distributed prior to fertilization

Why does the oocyte have asymmetrical bicoid?

because the nurse cell produces bicoid mRNA to the oocyte from one side

What is Bicoid?

Functions as a transcription factor

What does asymmetrical distribution mean?

activated only in certain regions

Bicoid morphogen determines anterior position. What happens if Bicoid is mutated?

No head structure

What is the Phase 2?

When phase 2 is completed, we see body segments.

What are the three kinds of segmentation genes in Phase 2?

Gap genes, pair-rule genes, and segment-polarity genes

• they are all transcription factors

• get more complicated as the name gets longer

What is phase 3?

Segment characteristic

• each segment produces characteristic structure

What type of genes are acting in phase 3?

Homeotic genes→ responsible for segment characteristics/ cell fate

What if there are mutations in the homeotic genes?

It will alter the cell’s fate/segment structure

What is an example of a mutation in homeotic genes?

Bithorax mutant

What do Homoeotic genes encode?

Homeotic proteins that function as transcription factors

• regulate transcription of specific genes that promote developmental changes

What is the homeobox?

Homeobox binds to DNA to control transcription. DNA-binding domains of all homeotic genes are conserved.