Tetrad Analysis-Part I-Ordered Tetrad Analysis
Ordered tetrad analysis is done in Neurospora. 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.
At 15:29 an example is given on how to do the calculation for ordered tetrad analysis and find out recombination frequency.
Formula for finding Recombination Frequency = Number of cross over product / Total number of offsprings x 100
Remember to divide the RF value by two to half the frequency.
Watch the unordered tetrad analysis video.