Development III

Question 1

What are hox genes

Answer 1

Deeply conserved group of transcription factors that occur as clutsers ina linear order in the chromosome.

Question 2

Describe the structure of hox genes

Answer 2

Group of evolutionary conserved TFs that occur in clusters along the chromosome. They all contain a homeodomain - 60 alpha helices DNA binding motif.

Question 3

What do hox genes code for

Answer 3

Hox genes code forbody plans that are symmetrical along a head tail axis.

Question 4

Explain why homeotic mutations are rarely seen in vertebrates?

Answer 4

Because in vertebres, one body part is encoded by multiple genes.

Question 5

Define homeotic tranformation

Answer 5

When you knock out a hox gene it causes one body part to develop into another.

Question 6

What is responsible for producing a homeotic transformation

Answer 6

Hox gene knockouts.

Question 7

What is the drosophila bithorax mutation

Answer 7

halters are formed where the notum and wings are found.

Question 8

What is the Drosophila antennapedia complex mutation

Answer 8

legs are formed instead of antennae.

Question 9

The anterior posterior axis which contains three segnemts, what are they? Anterior =?? Posterior = ??

Answer 9

Anterior = Head end

Posterior = rear end

Head, thorax and abdomen = 3 segments

Question 10

Define paralogous genes

Answer 10

Duplicated genes within a single genome

Question 11

Define orthologous genes

Answer 11

The same gene in different organisms. For example the insulin gene.

Question 12

Define homologous genes

Answer 12

Refers to the fact that for every gene, there is a maternal and paternal copy/ version.

Question 13

State the three mechanisms that give rise to a gene duplication event

Answer 13

Tandem gene duplication

Segmental gene duplication

Whole genome duplication.

Question 14

Explain Tandem gene duplication

Answer 14

Occurs due to unequal cross over caused by chromosome mis pairing at meiosis.

When two sequences are misalligned on the maternal and paternal homologue, unequal crossing may create a tandem repeat on one chromosome and a deletion on the other.

Question 15

Explain segmental gene duplication

Answer 15

Lots of tandem duplication that affects a whole chunk/section of the chromosome

Question 16

Explain whole genome duplication

Answer 16

Can be allotetraploid or autotetraploidy

Question 17

Explain how the 2 hox clusters in drosophila came to be

Answer 17

Both segmental and tandem gene duplication events have given rise to the 2 hox clusters.

Question 18

Define allotetraploid

Answer 18

Defined as the hybridization between two separate species.

Question 19

Define autotetraploid

Answer 19

Duplication of the genome through impoper meiosis

Question 20

Explain the 2R hypothesis

Answer 20

States that there were 2 rounds of whole genome duplication events in the vertebrate lineage.

2 rounds of chromosome duplications created 4 paralogous hox clusters. This hypothesis explains how the original hox cluster formed 4 hox clusters.

Question 21

How many hox clusters are present in humans and mice?

Answer 21

4 hox clusters

Question 22

How are these hox clusters arranged

Answer 22

4 hox clusters on 4 separate chromosomes.

Question 23

Define allotetraploidy

Answer 23

This is the hybridization between two separate species. Occurs in plants like cotton and rape. Here the genomes of both species are present in the gametes.

Question 24

Explain autotetraploidy

Answer 24

This is the duplication of the whole genome through improper meiosis.

Question 25

Explain subfunctionalization

Answer 25

This is the altering of a gene function following gene duplication.

Subfunctionalizaton can be caused by a change in protein sequence/change in time/place of expression or to mutated regulatory regions.

Question 26

Summarize the concept of the gene toolkit

Answer 26

Evolution has adopted the ancestral (old) function of hox genes and co-opted it to pattern the limbs.