Hox Genes, Patterning & Evolution

Question 1

What is mosaic development in insect embryos?

Answer 1

A form of embryonic development where cells have specific fates determined early in development.

Question 2

What are halteres in fruit flies?

Answer 2

The 3rd thoracic segment.

Question 3

What is the result of a mutation in the bithorax complex?

Answer 3

Transformation of the 3rd thoracic segment to a 2nd thoracic segment.

Question 4

What happens with a mutation in the antennapedia complex?

Answer 4

Legs form instead of antennae.

Question 5

Define homeotic mutations.

Answer 5

Transformations of one body part into another.

Question 6

What are Hox genes?

Answer 6

Genes first identified in Drosophila, causing homeotic transformations and are evolutionary conserved transcription factors.

Question 7

What is the homeodomain?

Answer 7

A 60 amino acid helix-turn-helix DNA binding motif.

Question 8

How do genes duplicate?

Answer 8

Through tandem gene duplication, subfunctionalization, and whole genome duplication events.

Question 9

What are paralogous genes?

Answer 9

Duplicated genes within a single genome.

Question 10

What are orthologous genes?

Answer 10

Same gene in different organisms.

Question 11

What is the 2R hypothesis?

Answer 11

The hypothesis that two rounds of whole genome duplication events occurred in the vertebrate lineage.

Question 12

What are the consequences of Hox gene mutations in mammals?

Answer 12

They can lead to homeotic transformations, such as transforming lumbar vertebrae to thoracic vertebrae.

Question 13

What is the significance of Hox gene expression patterns?

Answer 13

They provide positional identity along the anterior-posterior axis.

Question 14

How many Hox genes are present in humans or mice?

Answer 14

39 Hox genes.

Question 15

What is the role of the Hox gene toolkit?

Answer 15

To control anterior-posterior patterning and acquire novel functions.

Question 16

What is the result of mutations in paralogous Hox genes?

Answer 16

Dramatic disruptions of limb skeletal morphology.

Question 17

What is synpolydactyly?

Answer 17

A phenotype caused by mutation in HOXD13, leading to extra digits.

Question 18

What are the general rules about vertebrate Hox genes?

Answer 18

Generated through duplication events, expressed in spatial domains, overlap in expression domains, and show spatial and temporal colinearity.

Question 19

Fill in the blank: Hox genes are expressed in distinct ______ patterns.

Answer 19

proximal-distal

Question 20

True or False: Hox genes are only markers of the A-P axis.

Answer 20

False

Question 21

What is gene redundancy?

Answer 21

The phenomenon where duplicated genes can compensate for each other, making mutations less severe.

Question 22

What is the role of cis regulatory elements in gene duplication?

Answer 22

They can change the time and place of gene expression.

Question 23

What do mutations in regulatory regions lead to?

Answer 23

New expression domains or changes in timing of expression.

Question 24

How many Hox clusters evolved from the ancestral set?

Answer 24

Four clusters from a set of 13.

Question 25

What is the relationship between Hox gene expression and anatomical features?

Answer 25

Strong correlation exists, as Hox gene expression influences anatomical development.

Question 26

What is the evolutionary significance of Hox genes?

Answer 26

They are involved in anterior-posterior patterning and are conserved across species.