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

Define homeotic mutations.

Answer 2

Transformations of one body part into another.

Question 3

Where did Hox genes first come from?

Answer 3

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

Question 4

What is the homeodomain?

Answer 4

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

Question 5

How do genes duplicate?

Answer 5

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

Question 6

What are paralogous genes?

Answer 6

Duplicated genes within a single genome.

Question 7

What are orthologous genes?

Answer 7

Same gene in different organisms.

Question 8

What is the 2R hypothesis?

Answer 8

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

Question 9

What are the consequences of Hox gene mutations in mammals?

Answer 9

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

Question 10

What is the significance of Hox gene expression patterns?

Answer 10

They provide positional identity along the anterior-posterior axis.

Question 11

How many Hox genes are present in humans or mice?

Answer 11

39 Hox genes.

Question 12

What is the role of the Hox gene toolkit?

Answer 12

To control anterior-posterior patterning and acquire novel functions.

Question 13

What is the result of mutations in paralogous Hox genes?

Answer 13

Dramatic disruptions of limb skeletal morphology.

Question 14

What is synpolydactyly?

Answer 14

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

Question 15

What are the general rules about vertebrate Hox genes?

Answer 15

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

Question 16

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

Answer 16

proximal-distal

Question 17

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

Answer 17

False

Question 18

What is gene redundancy?

Answer 18

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

Question 19

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

Answer 19

They can change the time and place of gene expression.

Question 20

What do mutations in regulatory regions lead to?

Answer 20

New expression domains or changes in timing of expression.

Question 21

How many Hox clusters evolved from the ancestral set?

Answer 21

Four clusters from a set of 13.

Question 22

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

Answer 22

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

Question 23

What is the evolutionary significance of Hox genes?

Answer 23

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

Question 24

What are Hox genes?

Answer 24

A group of genes that control how the body develops in early growth, determining where body parts like the head, arms and legs form

Question 25

What is tandem duplication?

Answer 25

A type of genetic mutation where a segment of DNA is copied and the duplicate is placed right next to the original sequence. E.g. Original sequence = ABCD After tandem duplication = ABCBCD

Question 26

How does tandem duplication affect Hox genes?

Answer 26

Tandem duplications involving Hox genes can disrupt their normal function, leading to developmental abnormalities or disease Can create new Hox genes by copying an existing Hox gene and placing the copy next to it. Over time, the copies change slightly giving them new roles and creating clusters of Hox genes.

Question 27

What is segmental duplication?

Answer 27

A large chunk of DNA is copied and inserted into another part of the genome. These often contain multiple genes or other important DNA sequences Can lead to genetic variation and sometimes contribute to evolution but may also cause disease if they disrupt normal gene function

Question 28

How does segmental duplication affect Hox genes?

Answer 28

May copy clusters of Hox genes which can evolve to take on specialised roles in controlling body development

Question 29

What are spatial domains?

Answer 29

Regions along the Anterior-Posterior axis (AP) where the Hox genes are active Where Hox genes at the front = control structures near the head Hox genes at the middle and back = control structures in trunk and tail This ensures the correct body parts form in the right location along the AP axis *AP = head-to-tail direction in an animal’s body*

Question 30

What are domain overlaps?

Answer 30

Where the expression of multiple Hox genes overlap in the same region along the AP axis, allowing Hox genes to work together to fine-tune the development of specific body parts or structures In vertebrae, the boundary between ribbed and ribless vertebrae is controlled by the overlapping Hox genes where the combinations determine the specific vertebrae identity

Question 31

How are vertebrae clusters arisen from 2 whole genome duplication (WGD) events?

Answer 31

- WDG events give vertebrae extra copies of their Hox genes - Allows Hox genes to expand and specialise to form different types of vertebrae in the spine (i.e. the neck, back and lower back) - The extra Hox genes help control where each type of vertebrae would form - Creating different regions of the spine Having extra copies of Hox genes creates partial redundancy as they would have the same job If one gene is missing, the extra copy can step in and do the same job so the body still develops properly

Question 32

What is spatial collinearity?

Answer 32

The idea that the order of genes in a gene cluster (like Hox gene clusters) matches the order in which they are expressed along the body’s AP axis during development Refers to the physical location of genes on the chromosome and how this relates to their expression in the body

Question 33

What is temporal colinearity?

Answer 33

Hox genes are switched on in the same order they appear on the chromosome Refers to timing of when genes are activated

Question 34

What are the types of whole genome duplication events?

Answer 34

Allotetraploidy = hybridisation between 2 separate species followed by failure in meiosis Autotetraploidy = duplication of genome through improper meiosis

Question 35

What are homologous genes?

Answer 35

Genes that share a common ancestral gene