Hox Genes, Patterning & Evolution Flashcards
What is mosaic development in insect embryos?
A form of embryonic development where cells have specific fates determined early in development.
Define homeotic mutations.
Transformations of one body part into another.
Where did Hox genes first come from?
Genes first identified in Drosophila, causing homeotic transformations and are evolutionary conserved transcription factors.
What is the homeodomain?
A 60 amino acid helix-turn-helix DNA binding motif.
How do genes duplicate?
Through tandem gene duplication, subfunctionalization, and whole genome duplication events.
What are paralogous genes?
Duplicated genes within a single genome.
What are orthologous genes?
Same gene in different organisms.
What is the 2R hypothesis?
The hypothesis that two rounds of whole genome duplication events occurred in the vertebrate lineage.
What are the consequences of Hox gene mutations in mammals?
They can lead to homeotic transformations, such as transforming lumbar vertebrae to thoracic vertebrae.
What is the significance of Hox gene expression patterns?
They provide positional identity along the anterior-posterior axis.
How many Hox genes are present in humans or mice?
39 Hox genes.
What is the role of the Hox gene toolkit?
To control anterior-posterior patterning and acquire novel functions.
What is the result of mutations in paralogous Hox genes?
Dramatic disruptions of limb skeletal morphology.
What is synpolydactyly?
A phenotype caused by mutation in HOXD13, leading to extra digits.
What are the general rules about vertebrate Hox genes?
Generated through duplication events, expressed in spatial domains, overlap in expression domains, and show spatial and temporal colinearity.
Fill in the blank: Hox genes are expressed in distinct ______ patterns.
proximal-distal
True or False: Hox genes are only markers of the A-P axis.
False
What is gene redundancy?
The phenomenon where duplicated genes can compensate for each other, making mutations less severe.
What is the role of cis regulatory elements in gene duplication?
They can change the time and place of gene expression.
What do mutations in regulatory regions lead to?
New expression domains or changes in timing of expression.
How many Hox clusters evolved from the ancestral set?
Four clusters from a set of 13.
What is the relationship between Hox gene expression and anatomical features?
Strong correlation exists, as Hox gene expression influences anatomical development.
What is the evolutionary significance of Hox genes?
They are involved in anterior-posterior patterning and are conserved across species.
What are Hox genes?
A group of genes that control how the body develops in early growth, determining where body parts like the head, arms and legs form
What is tandem duplication?
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
How does tandem duplication affect Hox genes?
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.
What is segmental duplication?
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
How does segmental duplication affect Hox genes?
May copy clusters of Hox genes which can evolve to take on specialised roles in controlling body development
What are spatial domains?
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
What are domain overlaps?
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
How are vertebrae clusters arisen from 2 whole genome duplication (WGD) events?
- 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
What is spatial collinearity?
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
What is temporal colinearity?
Hox genes are switched on in the same order they appear on the chromosome
Refers to timing of when genes are activated
What are the types of whole genome duplication events?
Allotetraploidy = hybridisation between 2 separate species followed by failure in meiosis
Autotetraploidy = duplication of genome through improper meiosis
What are homologous genes?
Genes that share a common ancestral gene
