Vector Biology And Genetics Flashcards
What makes a mosquito a good malaria vector?
- Anthropophagic
- Endophilic
- Endophagic
- High frequency of biting
- High susceptibility to infection
- High vector density
What does anthropophagic mean?
Preferentially feeds on humans
What does endophilic mean?
Rest indoors, associated with the domestic environment
What does endophagic mean?
Feeds indoors
What is vectorial capacity?
It is a measure of the efficiency of vector-borne disease transmission. It can be summarised as a mathematical equation
What are the factors contributing to vectorial capacity?
Mostly genetic
- Vector density
- Vector biting frequency
- Female lifespan
- Extrinsic incubation cycle
- Interval between feeding
What is the most important factor which impacts vectorial capacity?
The extrinsic incubation period
What is the extrinsic incubation period?
It is the latent period of the parasite in the mosquito
What is a species complex?
A group of morphologically indistinguishable species which are closely related
What is the species complex in Africa?
A. gambiae sensu lato
How many species belong to the A.gambiae species complex?
7
Which species belonging to the species complex is the most efficient vector for Plasmodium falciparum spread?
A.gambiae sensu stricto
Anopheles species complex properties?
- Related species
- Morphologically related
- Vary in behaviour
- Vary in vector competence
- Vary in spatial/temporal associations
What do the members of the A.gambiae complex vary in?
Behaviour, vector competence, spatial/temporal associations
Population structure of A.gambiae complex?
Sympatric population structure- means that the species are present in the same area, they encounter one another
What does sympatric mean?
The species exist in the same geographical area
The members of the A.gambiae complex are different species as defined by?
The biological species concept
They are reproductively isolated
Mosquitos belong to which order?
Diptera
What are polytene chromosomes?
These are giant chromosomes which have visible bands
How do polytene chromosomes form?
Endoreduplication
There is DNA replication but there is no cell division
What is thought to be the function of polytene chromosomes?
Allows larvae to develop much faster
What is endoreduplication?
Rounds of DNA replication without cell division
What can occur in polytene chromosomes?
Chromosomal inversions
What are chromosomal inversions and how do they form?
Form from two cuts occurring in a chromosome
Chromosomal inversions form when a segment of a chromosome becomes reorientated 180 degrees from the normal
Pericentric inversions?
Include the centromere
Paracentric inversions?
Do not include the centromere
Issues of being an inversion heterozygote?
Looping out
Inversion loops form due to incorrect alignment
Homologous recombination purpose?
To generate genetic diversity
To allow for different combinations to occur
What is the issue associated with recombination occurring within chromosomal inversions?
Formation of acentric and dicentric chromatids
Acentric chromatid?
No centromere
Dicentric chromatid?
Two centromeres
The products of recombination within an inverted repeat are?
Non-viable
As the products of recombination within an inverted repeat are non-viable what occurs?
There is cross-over suppression
As a result of cross-over suppression?
As a result of cross-over suppression the genes in the inversion are genetically linked
What is genetic linkage?
Linkage is when genes located close together on a chromosome are inherited together
The tendency for genes located close together on a chromosome to be inherited together is known as?
Genetic linkage
What is the overall effect of chromosomal inversion?
- Cross-over suppression
- Tight linkage in the inverted segment as a result
What is a co-adapted gene complex?
A particular set of alleles at several genes on a chromosome that makes the individuals possessing them very well adapted
What threatens to break-up a co-adapted gene complex?
Every cycle of meiosis
Genetic recombination
What can protect a co-adapted gene complex?
If it occurs within an inverted segment where there is cross-over suppression
There is very tight linkage of genes in?
An inverted chromosomal segment
What are the two distinct forms of A.gambiae sensu stricto?
Mopti
Savannah
What is the main difference between Mopti and Savannah?
Differential habitat preference
Mopti prefers?
Semi-permanent bodies of water e.g. man made larval habitats such as rice fields or flooded areas
Savannah prefers?
Temporary larval habitats such as puddles and other rain dependent sites
What is thought to cause this differential habitat preference?
The chromosomal inversions associated with Savannah forms on Chr 2R… believed there is an associated co-adapted gene complex
Are the M and S forms reproductively isolated?
Not in the lab
In the lab the crosses are viable and fertile
Why are no M and S hybrids observed in the wild?
Due to pre-mating reproductive isolation mechanisms
Are the M and S hybrids separate species?
They are not yet separate species but they are at the early stages of speciation
Why is it important to know if they are reproductively isolated or not?
- Important for gene drives etc…
- Important for the spread of resistance
What allele confers resistance to pyrethroid insecticides?
kdr
knockdown resistance allele
How has the kdr allele spread?
Originated in the S form
Now present in the M form
How did the kdr allele enter the M form?
Introgression
What is linkage?
Linkage is the tendency for genes/DNA that are closely associated on a chromosome to be inherited together
What are QTLs?
There are loci which contain various genes contributing to a particular phenotype
How are QTLs mapped?
By identifying molecular markers and associating them with certain phenotypes
What are two markers which could be used?
SNPs
Microsatellites
Which marker type is more polymorphic?
Microsatellites
Once you find a QTL how do you find the causative gene?
Home in on the region and see if there are any genes already associated with the particular phenotype
Perform microarrays to see if there is differential expression of certain genes under specific conditions
