Bio 1-L15- Organising a Body Plan in Multicellular Organisms

examples of model organisms

• c elegans- for cell differentiation

• dropshphila- genetics studies

• frog- developmental biology

• mouse- mammal and has genome sequences

order of embryology

1. fertilisation

2. cleavage- rapid mitosis- hollow ball- blastula/blastoderm

3. gastrulation- movement of cells- 3 layers- endoderm, mesoderm nd ectoderm

4. neurulation- making of the neural tube and circulatory system

5. organogenesis

gastrulation - explain the 3 and what they give rise to

1. ectoderm- outer- skin, nervous system

2. mesoderm-middle- bone, blood, muscle

3. endoderm- inside- digestive and respiratory tract

how do cells receive info about relative position

1. induction- by paracrine and juxtacrine

what are homeotic genes and who discovered this?

• in mutants of these genes- the structures are in the wrong place

• Edward Louis- drosophila- alteration of homeotic genes and Hox genes gave rise to legs in the antennae region

what are hox genes

genes that encode transcription factors- and are genes mutated in homeotic mutants- control body parts

what are organisers in cells and 2 examples for limbs- who discovered this?

• organiser influences the development of surrounding tissue

  1. apical ectodermal ridge- AER- removing it seizes growth of limbs or if removed earlier- limbs grow shorter on P/D axis

  2. zone of polarising activity- ZP1- if transplanted on anterior- duplication of fingers

spennman- tests in chicks

AER- what happens when removed?

• the limb does not grow- along proximal to distal axis

ZPA- what is it and WHERE

• located in posterior mesoderm in developing limb bud

• if transplanted to anterior- it causes a duplication of digits

how are genes controlled in development- example model organism

1. maternal effect genes- establish the poles

2. segmentation genes- segmented units

3. homeotic gene- where different parts should be

in drosophila