15/ hox genes and EvoDevo

Question 1

why are our genomes so similar w other species but we are so different

Answer 1

changes in expression of common set of developmental genes

Question 2

how do we determine if proteins are similar, what does similar proteins suggest

Answer 2

• blast protein alignment
• input the aa sequence of protein in question
• blast program searches huge database
• shows alignment of a query protein to subject protein (zen)
• proteins evolved from the same common ancestor and proteins have similar molecular functions

Question 3

how many vertebrate fgfs? how many categories do they fall into, how many fgfs does a ciona (chordate) have, what does this suggest, how do they arise, what are copies called

Answer 3

• 22
• 4
• 4 - one from each group
• the common ancestor of the sea squid and vertebrate had 4 fgfs
• more fgfs arose due to gene duplication: polyploidy and local duplications
• new copies called paralogues

Question 4

how can an extra copy of a gene result in changes in expression

Answer 4

• we have a redundant gene - can change it while the original gene continues
• can change pattern of expression during development
• can change structure of the protein
• = gene neofunctionalism, driving force of morphological evolution

Question 5

why are changes in expression patterns of genes thought to play a major role in evolution

Answer 5

regulatory elements can be easily changed

Question 6

how can changes in enhancers alter gene expression

Answer 6

• example: new enhancer brought close to a gene
• this can add/delete sites by rearrangements, insertions, deletions or base pair substitutions
• but has to be v specific to form a working protein

Question 7

what are hox genes, how did they originate - how do we know, how are they expressed, what changes if their expression changes

Answer 7

• tfs found in clusters in the genome
• have sequence similarity - suggests they originated from same genome
• expressed in specific segments in the embryo
• changes in segmental identity - which segment makes which structure

Question 8

in vertebrates what hox gene is responsible for cervical (neck) and thoracic (chest) spine development

Answer 8

• cervical - hoxc5
• thoracic - hoxc6

Question 9

example of how hox expression changes change morphology

Answer 9

• expression of hoxc6 starts more posteriorly in chick - longer neck in chick and smaller chest

Question 10

how can changes in hox genes expression explain the loss of limbs in snake evolution

Answer 10

• snakes have 300 somites, while mice have 60
• snakes have no forelimb and severely reduced hindlimb
• in snakes, expression of hoxc6 and hoxc8 runs almost entirely throughout the snake and flank and thoracic expression fully overlap

Question 11

what apart from changes in hox expression can change morphology

Answer 11

size of vertebrae - eg giraffes have same number of vertebrae they’re just longer

Question 12

what explains how crustaceans have legs on their abdomen but insects don’t

Answer 12

• ubx evolution causes changes in protein expression
• in fly larvae, DIx tf specifies leg precursor cells
• ubx is expressed in the abdomen where it replaces DIx expression - it represses DIx expression
• NOT IN crustaceans - here function of ubx has changed
• ubx is expressed in abdomen of crustacean larvae but it doesn’t turn off DIx expression
• thought that ubx gene became able to repress DIx expression in an ancestor of drosophila