15 - Evo-devo

Question 1

What is evo-devo?

Answer 1

How development mechanisms evolved

Question 2

What are the two different kinds of regulatory elements?

Answer 2

• cis-acting -> elelments (enhancers/ silencers and promoter) proximal to the gene
• Trans-acting -> elements (TFs) encoded by distal regions, activators or repressors

Question 3

Explain the action of cis and trans elements when all TFs are the same

Answer 3

• TFs may work independently - the higher the number of TFs, the more likely a cis-factor is to be occupied by them - expression may be triggered at a lower TF concentration as only a few need to be bound
• TF binding may be cooperative - individual TFs may have a low affinity - stabilising interactions between TFs may increase binding - at low TF conc, low binding, at a specific concentration cooperative binding will come in, generates and S-curve

Question 4

Explain the action of cis and trans elements when there are different TFs

Answer 4

• different cis-elements might bind different TFs
• different inputs may regulate the cells in which a gene is transcribed
• also may regulate the level at which it is transcribed

Question 5

What is often the output of ligands binding to receptors?

Answer 5

• change in gene expression due to activation of TFs

Question 6

Explain the anterior-posterior axis development in fruit flies

Answer 6

• maternal effect genes - gradients from anterior to posterior - genotype of the mother patterns here
• Segmentation genes (gap genes) - defined broad regions
• pair-rule genes - defines 7 segments
• segment-polarity genes - defines 14 segments
• Homeotic genes - determines regional characteristics

Question 7

What is the effect of a mutation in the maternal effect genes?

Answer 7

• major disturbances in anteroposterior organisation

Question 8

What is the effect of a mutation in the segmentations genes (gap genes)?

Answer 8

• adjacent segments missing in major region of the body

Question 9

What is the effect of a mutation in the pair-rule genes?

Answer 9

• part of pattern deleted in every other segment

Question 10

What is the effect of a mutation in the segment-polarity genes?

Answer 10

• segments replaces by their mirror images

Question 11

What is the effect of a mutation in the homeotic genes?

Answer 11

• inappropriate structures forms for a given segmentation level

Question 12

Explain the role of the bicoid TF in development

Answer 12

• diffuses from anterior to posterior
• binds to enhancers of target gap genes
• individual nuclei share the same cytoplasm
• each gap gene has a different arrangement of cis elements for bicoid
• low affinity, only active at high concentrations
• if using cooperative binding, activates at low concentrations

Question 13

Give an example of a gap gene

Answer 13

hunch back gene

Question 14

Give an example of a pair rule gene

Answer 14

even-skipped

Question 15

Explain the function of the pair-rule and segment polarity genes

Answer 15

• different cis-elements
• each stripe is activated by a specific combination and concentration of inputs

Question 16

What do pair-rule genes regulate?

Answer 16

the expression of segment polarity genes

Question 17

What is the role of hox genes?

Answer 17

• determine the identity of repeater body units
• 8 genes in two complexes
• order of genes corresponds to order of body regions

Question 18

What is the genetic toolkit of development?

Answer 18

• patterning genes
• hox genes

Question 19

What is co-option?

Answer 19

using a pre-existing gene for a new function

Question 20

What is an evolutionary advantage to mutations in the enhancer?

Answer 20

• mutations in code would effect expression in all tissues
• many processes may be affects
• may impact biochemical function

Question 21

Name _ developmental constraints

Answer 21

• lack of a pathway in an organism
• traits show strong correlations with each other
• TFs binding to multiply genes creates pleiotropy