Ged: Dev Biol 3 Hox Genes, Patterning And Evolution

Front 1

Homeotic mutations?

Back 1

mutations which result in the transformation of one body structure or another

Structures are often perfectly formed, just in wrong place

Hint 1

Homo same

Front 2

Hox gene?

Back 2

family of genes that encode related transcription factors

characterised by containing a DNA binding domain called the homedomain/ homeobox

highly conserved in evolution

shown to be involved in anterior posterior patterning in dropshilia and other organisms

Front 3

what do the clusters of the hox genes in the genome show?

Back 3

the clusters show spatial and temporal relationships

genes in the 3' end are expressed before those in the 5' of the cluster

Front 4

homologous genes?

Back 4

genes that share a common ancestoral gene

Front 5

paralogous genes?

Back 5

genes that have been duplicated within a single genome

pairs and pairs in same genome

Front 6

orthologous genes?

Back 6

same genes in different organisms

others have same

Front 7

Gene redundancy?

Back 7

a situation where no change in phenotype is observed when a gene is mutated

this is because another gene (usually a paralouge) can replace the function of the mutated gene

thus the presence of a paralogous gene masks the presence of the mutated one

this kind of interaction is known as using one of the genes available in the genetic toolkit of the organism

Front 8

how can dev biol use genetics to identify genes involved in development|?

Back 8

when a mutation causes a disease phenotype to occur it can show what the mutated gene is responsible for

if a mutation results in loss of eye function, that gene is responsible for normal eye functioning

not that: often name for a gene is its loss of function phenotype

Front 9

how can genes duplicate?

Back 9

1) Tandem gene duplication: where a gene is replicated many times,

2) Segmental duplication: affects large portions of the chromosome ( like giant tandem duplication)

3) Whole genome duplication events

Front 10

In which ways can whole genome duplication events occur?

Back 10

1) Allotetraploidy = hybridisation between two seperate species (allo-diff)

2) Autotetreploidy = single individual ( duplication of genome through improper meiosis)

autotetraploidy can only occur if diploid state is maintained, so haploid gametes can be produced

Front 11

what normally happens to a gene that has been replicated?

Back 11

the genes is normally removed unless it gains a new function- subfunctionalisation

duplication and diverge

Front 12

what are the mechanisms for subfunctionisation of a duplicated gene?

Back 12

1) change protein sequence of product

new protein has new function, different binding etc

2) Change time / place of expression

cis regulatory regions are also duplicated, somehow these are changed, altering when and where these genes are expressed

Front 13

how have the hox genes co-opted in the mammalian genome?

has thier function been conserved at all?

Back 13

responsible for limb patterning in mammals

genes expressed in anterior of drosphi also expressed in anterior of mouse, same for posterior

their function has been somewhat conserved

now also involved in proximal-distal development of limbs

Front 14

Once gene has subfuntionalised, does it loose its original function?

Back 14

note subfunctionalisation is also refered to as the aquisition of novel functions

often it does not loose its original function

it becomes part of the genetic tool kit of an organism

Front 15

is their any correlation between hox genes and anatomical features of organisms?

Back 15

Using comparative anatomy of mouse and a chicken,

Chick has 14 cervical vert

mouse has 7,

the chick genome has many more hox genes associated with cervical vert development

Strong correlation between hox genes and anatomical features

Front 16

How do we find out if hox genes are only markers of ant-post positioning, or if they are direction involved with A-P positioning

that they are directly involved?

Back 16

easier method is to study the effects of mutations in hox genes for mammals,

mutations in the hox genes change ant-post patterning

Front 17

What is the issue with studying the function of hox genes, but looking at example with mutations?

Back 17

often there are more than one of each hox gene

therefore if one has a mutation, redundancy of a paralogous gene kicks in an normal function may still be maintained

therefore all paralogues of that hox will have to be removed, mutated for its functioning to be fully understood

removing all paralouges removes problem of redundancy