Lecture 20. Evo-Devo: How body plans can change through evolution ?

Question 1

What is evo-devo ?

Answer 1

The synthesis of the study of evolution and developmental biology

Question 2

How is development is regulated ?

Answer 2

Through transcriptional control and regulatory networks

Question 3

What regions of genes are important ?

Answer 3

The control regions and not just the coding regions

Question 4

What are developmental regulatory genes referred to as ?

Answer 4

The genetic toolkit for development

Question 5

What do regulatory genes make up ?

Answer 5

A fraction of all genes

Question 6

What do regulatory genes encode ?

Answer 6

Either transcription factors or components of signaling pathways

Question 7

What is the spatial and temporal pattern of regulatory gene expression closely correlated ?

Answer 7

Regions in the animal where the gene functions

Question 8

What are the three types of changes in developmental regulatory genes that might bring about changes in body plan ?

Answer 8

1. Change in number of genes
2. Change in the timing and spatial domain of expression
3. Change in gene interaction

Question 9

What was discovered about multicellular animals with organised body plans ?

Answer 9

Contain clusters of Hox genes

Question 10

How many hox clusters do invertebrates have ?

Answer 10

A single Hox cluster

Question 11

What happened around 520 million years ago to allow elaboration of the vertebrate body plan ?

Answer 11

Postulation - Cluster duplication

Question 12

What happens after postulation ?

Answer 12

A second duplication around 425 million years ago yielded four clusters

Question 13

What does gene duplication facilitate ?

Answer 13

Evolutionary change

Question 14

What does the presence of more hox genes arranged in additional clusters allow ?

Answer 14

The evolution of more complex and new body parts

Question 15

What does the change in spatial expression show us ?

Answer 15

Examine the expression of Hox genes in various species can shed further light on how body parts were gained or modified or lost

Question 16

What are the two main derived features of snakes ?

Answer 16

1. limblessness

2. Vertebrae are all of the thoracic type and bear ribs

Question 17

What is the hox positional code of snakes ?

Answer 17

Complex overlapping expression of 39 hox genes in different anterior posterior locations

Question 18

How has the hox code gene expression in snakes changed ?

Answer 18

Expansion of Hox gene expression domains along the body axis giving thoracic type code at all points. Also removes the cue to make a forelimb

Question 19

How are snakes hindlimbs believed to be lost ?

Answer 19

Regression

Question 20

How do we get out fingers and toes ?

Answer 20

Limbs with fingers/toes acquired a new region of hox gene expression at the distal end of the limb to allow digits to be patterned

Question 21

How could changes in spatial expression occur ?

Answer 21

By changing the control regions - enhancers driving expression of the hox genes in the embryo

Question 22

What is extremely important in the evolution of body plans ?

Answer 22

Control regions can also evolve

Question 23

What do marine spined sticklebacks have ?

Answer 23

Ventral spines to protect from predators

Question 24

What do lake sticklebacks have ?

Answer 24

Reduced or absent spines

Question 25

What has causes this recent change in stickleback body plans ?

Answer 25

Lake sticklebacks have specifically lost expression of pitx 1 where ventral spines would form instruction to make a spine. This is missing

Question 26

What is pax 6 ?

Answer 26

The master regulator of eye development

Question 27

What type of gene is pax 6 ?

Answer 27

A homeobox gene

Question 28

What is a mutation in pax6 in drosphilia called ?

Answer 28

Eyeless

Question 29

What does the mutation in pax 6 in drosphilia lead to ?

Answer 29

Leads to loss of eyes

Question 30

What is the mutation in pax 6 lead to ?

Answer 30

A phenotype called small eye in the heterozygous state

Question 31

What does the mutation in pax 6 in humans cause ?

Answer 31

Aniridia, a malformation of the iris

Question 32

What does forced expression of the pax 6 gene in drosphilia on the leg or antenna lead to ?

Answer 32

The formation of extra ectopic eyes in that site

Question 33

Where is Ubx expressed in insects ?

Answer 33

Abdominal segements

Question 34

What does Ubx do in abdominal segments in insects ?

Answer 34

Suppresses limb formation

Question 35

Where is Ubx expressed in arthropods other than insects ?

Answer 35

Expressed in abdominal segments

Question 36

What does the Ubx do in arthropods other than insects ?

Answer 36

It does not suppress leg formation

Question 37

What influences changes in protein sequences of Ubx activity as an activator/ repressor ?

Answer 37

Sequence comparisons

Question 38

What allows changes in the body plan of organisms ?

Answer 38

Changes in the activity of a positional regulatory gene

Question 39

What creates morphogenesis ?

Answer 39

Differential growth rates

Question 40

What is meant by a homologous structure ?

Answer 40

Structures that arise from same structure in common organisms

Question 41

What can the different relative sizes and shapes of homologous structures be changed by ?

Answer 41

The length of time a particular signaling pathway or organising centre such as AER is active

Question 42

What are the shapes of skeletal rudiments sensitive to ?

Answer 42

Mechanical stimulation which can be seen in the hippo pathway