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 organisms. Use of modern
microscopy and
micromanipulation techniques allows the four haploid 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. Since the frequency of tetrad segregation types is influenced by the recombination frequency for the two markers, the segregation data can be used to calculate the genetic distance between the markers if they are close on the same chromosome. Tetrad analyses have also contributed to detection and study of the phenomena of gene conversion and post-meiotic segregation. These studies have proven central to understanding the mechanism of meiotic recombination, which in turn is a key to understanding the adaptive function of sexual reproduction. The use of tetrads in fine-structure genetic analysis is described in the articles
Neurospora crassa and
Gene conversion.
General procedure Crosses are performed between haploid MATa and MATα
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.
Tools Traditionally, tetrad dissection has a reputation as "black 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 glass fiber needle to which the spores adhere due to the formation of a water
meniscus between the
agar and the needle. ==See also==