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Tetrad (genetics)
 
 
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The tetrad is the four spore
Spore

In biology, a spore is a reproduction structure that is adapted for biological dispersal and surviving for extended periods of time in unfavorable conditions....
s of a yeast
Yeast

Yeasts are eukaryote microorganisms classified in the Kingdom fungus, with about 1,500 species currently described; they dominate fungal diversity in the oceans....
, that separate after mating. If the two parents have a mutation in two different genes, the tetrad can segregate as the parental ditype, the non-parental ditype or as the tetratype.
trad type containing two different genotypes, both of which are parental. A spore arrangement in Ascomycetes that contains only the two non-recombinant-type ascospores.

ore arrangement in Ascomycetes that contains only the two recombinant-type ascospores (assuming two segregating loci).






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The tetrad is the four spore
Spore

In biology, a spore is a reproduction structure that is adapted for biological dispersal and surviving for extended periods of time in unfavorable conditions....
s of a yeast
Yeast

Yeasts are eukaryote microorganisms classified in the Kingdom fungus, with about 1,500 species currently described; they dominate fungal diversity in the oceans....
, that separate after mating. If the two parents have a mutation in two different genes, the tetrad can segregate as the parental ditype, the non-parental ditype or as the tetratype.

Parental ditype

A tetrad type containing two different genotypes, both of which are parental. A spore arrangement in Ascomycetes that contains only the two non-recombinant-type ascospores.

Non-parental ditype

A spore arrangement in Ascomycetes that contains only the two recombinant-type ascospores (assuming two segregating loci). A tetrad type containing two different genotypes, both of which are recombinant.

Tetratype

A Tetratype is a tetrad containing four different genotypes, two parental and two recombinant. A spore arrangement in Ascomycetes that consists of two parental and two recombinant spores indicating a single crossover between two linked loci.

Linkage analysis

The ratio between the different types arising after the sporulation is a measure of the linkage
Genetic linkage

Genetic linkage occurs when particular genetic Locus or alleles for genes are inherited jointly. Genetic loci on the same chromosome are physically connected and tend to stay together during meiosis, and are thus genetically linked....
 between the two genes.

Tetrad Dissection

Tetrad Dissection has become a powerful tool of yeast geneticists, and is used in conjunction with the many established procedures utilizing the versatility of yeasts as model organism
Model organism

A model organism is a species that is extensively studied to understand particular biology phenomena, with the expectation that discoveries made in the organism model will provide insight into the workings of other organisms....
s. Use of modern microscopy
Microscopy

Microscopy is the technical field of using microscopes to view samples or objects. There are three well-known branches of microscopy, optical microscopy, electron microscopy and scanning probe microscopy....
 and micromanipulation
Micromanipulator

A micromanipulator is a device which is used to physically interact with a sample under a microscope, where a level of precision of movement is necessary that cannot be achieved by the unaided human hand....
 techniques allows the four hapoid spores of a yeast tetrad to be separated and germinated individually to form isolated spore colonies.

Uses

Tetrad analysis can be used to confirm whether a phenotype is caused by a specific mutation, construction of strains, and for investigating gene interaction.

General Procedure

Crosses are performed between haploid MATa and MATa mating strains, then the resulting diploids are transferred to sporulation media to form a tetrad containing four haploid spores. Tetrads can then be prepared with Zymolyase, or another enzyme, to digest the wall of the ascus. The spores are then separated with a micromanipulator needle and deposited in separate positions on a petri dish
Petri dish

A Petri dish is a shallow glass or plastic cylindrical lidded dish that microbiologists use to microbiological culture cell s. It was named after Germany bacteriologist Julius Richard Petri, who invented it when working as an assistant to Robert Koch....
.

Tools

Traditionally, tetrad dissection has a reputation as "dark art" . However, instruments have since been developed specifically for tetrad dissection; the most advanced allow easy and semi-automated separation of tetrads . Most micromanipulators use a fiberglass needle to which the spores adhere due to the formation of a water meniscus
Meniscus

Meniscus, plural: menisci, from the Greek language for "crescent", is a curve in the surface of a molecular substance and is produced in response to the surface of the container or another object....
 between the agar
Agar

Agar or agar agar is a gelatinous substance derived from seaweed. Historically and in a modern context, it is chiefly used as an ingredient in desserts throughout Japan, but in the past century has found extensive use as a solid substrate to contain Growth medium for microbiology work....
 and the needle.

See also

  • yeast
    Yeast

    Yeasts are eukaryote microorganisms classified in the Kingdom fungus, with about 1,500 species currently described; they dominate fungal diversity in the oceans....
  • Model organism
    Model organism

    A model organism is a species that is extensively studied to understand particular biology phenomena, with the expectation that discoveries made in the organism model will provide insight into the workings of other organisms....
  • synthetic genetic array
    Synthetic genetic array

    Synthetic Genetic Array analysis is a high-throughput technique for exploring synthetic lethality and synthetic sick genetic interactions . SGA allows for the systematic construction of double mutants using a combination of Recombinant DNA, mating and selection steps....

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