Tetrad Analysis-Part II-Unordered Tetrad Analysis
Unordered Tetrad Analysis is done in yeast. Basically, Tetrad analysis is used for gene mapping in case of haploid system. In tetrad analysis, the gene mapping is done by measuring the distance of gene of interest from a centromere. Centromere is a great reference point because it does not show crossing over and shift in position. Once we established distance of gene of interest then we can measure distance of other genes form the gene of interest.
Tetrads are of two types. Tetrads in which the spores are arranged according to the order in meiotic division are called ordered tetrads. This is observed in Neurospora. Whereas the order or arrangement is not specific are called unordered tetrads. This is observed in yeast.
Neurospora has an interesting reproductive patter. It undergoes two rounds of meiotic divisions followed by a single round of mitosis and this results in production of 8 haploid asci spores at the end of reproductive cycle whereas yeast stops after meiotic division and produces four spores at the end.
The video explains terms such as Parental Ditype (PD), Non parental Ditype (NPD) and Tetratype (TT). At 03:21 an example is given on how to do the calculation for unordered tetrad analysis and find out recombination frequency.
Formula for Recombination Frequency = 1/2 of number of TT asci + number of NPD asci / Total number of asci x 100
If you missed the introduction on tetrad analysis and types of tetrads, watch the video on Ordered Tetrad Analysis.