DEVELOPMENTAL BIOLOGY

Question 1

What is the preformation theory?

Answer 1

that fertilised egg or sperm contains a preformed miniature version of the adult

Question 2

What is theory of epigenesis?

Answer 2

that the adult spontaneously emerges from a fertilised egg as ‘fresh formation’

Question 3

As development proceeds, cell fates become more _(a)___ and determined.

Answer 3

restricted

Question 4

What is a development organiser?

Answer 4

signalling cells that induce the development program of surrounding cells

Question 5

What was the evidence for a development organiser?

Answer 5

grafting experiments in early newt embryos; blastopore cells transplanted to another embryo in regions that would become ventral side, produced second embryo

Question 6

What are ‘toolkit genes’? These were identified using what methodology?

Answer 6

genes involved in embryo patterning

• a genetic screen in Drosophila

Question 7

‘Toolkit’ genes make up a (a) fraction of the genome and are (b) conserved among distantly related species. These are often expressed during different (c) of development and will usually encode (d) or signalling molecules such as ligands.

Answer 7

a) small
b) widely
c) times
d) transcription factors

Question 8

What is the pax6 gene?

Answer 8

• a gene that controls eye development via a transcription factor
• highly conserved between humans and drosophila

Question 9

4 key characteristics of transcription factors

Answer 9

1) they are proteins and modular in fashion, with highly conserved DNA binding domains
2) come in large gene families, each with a developmental function
3) each have specific DNA binding sequences, occasionally forming hetero or homodimers with related transcription factors
4) usually contain transcription activation or repression binding sites in order to recruit DNA pol

Question 10

Many mutations that alter development, are mutated in genes that encode for ___ ___.

Answer 10

transcription factors

Question 11

a) What does agamous mean?
b) An Ag Arabidopsis mutant has ___ & ___ instead of stamens and carpels
c) the agamous protein is an example of a __ ___ and is usually highly localised to which area of the plant?

Answer 11

a) no sex organs

b) sepals
carpels

c) transcription factors
- centre of flowers

Question 12

Describe the structure of the DNA binding MADS box?

Answer 12

• has a highly conserved structure as a helix - beta loop - helix
• beta loop mediates dimerisation

Question 13

a) What are enhancers?

b )What are their function?

c) The agamous gene has an enhancer region for the binding of the transcriptional factor __. When this is mutated, then Ag expression is ___.

Answer 13

• discrete DNA regions upstream of core promoter and define b) where and when a gene is expressed

c) WUS
- inhibited

Question 14

What are reporter genes (naive)?

Answer 14

genes that encode a recognisable product

Question 15

How do differences between cells originate?

Answer 15

• secreting a varied gradient of extracellular ligands

Question 16

Describe how intercellular signalling pathways operate?

Answer 16

1. the receptor for the signalling molecule is typically a membrane bound protein that has a binding pocket for ligands
2. ligand binds to the protein which causes a conformational change
3. which releases an intracellular signal, such as a kinase that alters proteins and causes an alteration in gene expression through transcription

Question 17

a) Give an example of a membrane bound protein that is highly conserved.
b) What does the ligand binding lead to?
c) what does hh code for?
d) What is the organiser?

Answer 17

a) PATCHED (PTC) in hedgehod
b) leads to complicated phosphorylation cycles, and release of Cubitus Interruptus (Ci) activating target genes in the nucleus
c) a small diffusible protein signal
d) ZPA