Tetrad analysis

tetrad analysis and problems

1. Tetrad analysis Manjunatha S I M.Sc.(Botany) University of Mysore Mysuru

2. Contents Introduction Organisms used and Advantages Analysis of tetrads Problem References

3. Introduction C ertain species of lower Eukaryotes such as algae and fungi which spend most of their lifecycle in haploid state, have also been used in mapping studies. Fungi can also reproduce sexually and produces 4 sexual spores which are haploid known as Tetrad . In some, meiosis is followed by mitosis to form 8 spores known as O ctad .

4. Organisms used Lower Eukaryotes such as Algae and Fungi Especially in Fungi, Sachharomyces cerevisiae , Coprinus lagopus Chlamydomonas reinhardtii (Tetrads) and Neurospora crassa Aspergillus nidulans ( Octads ) are used extensively

5. Got many Advantages...!!!! Potential for analyzing all of the products from each meiotic division. H aploid in nature. P roduce very large numbers of progeny. The life cycles of these organisms tend to be short. Can make direct observations on the behavior of genes during meiosis, can examine cross-overs . C an map centromeres.

6. Analysis of Unordered Tetrads Unordered tetrad : Ascus provides enough space for tetrads to randomly mix together Eg : Sachharomyces cerevisiae

7. AB AB ab ab P arental ditype or PD . Ab Ab aB aB Nonparental ditype or NPD. AB Ab aB ab T etratype,or TT

8. Class I Class II Class III Class IV Class V Class VI 2 18 28 4 16 32 ade + + ade + tyr ade + tyr ade his + ade his tyr ade his tyr ade + + ade + + ade + tyr ade his + ade his + ade his tyr + his tyr + his tyr + his + + + tyr + + + + + + + his tyr + his + +his + + + tyr + + tyr + + + Check whether the genes are linked or not and also Calculate the distance between the genes

9. Analysis of Ordered tetrads Ordered tetrad : Tight Ascus is produced which prevents spores from randomly moving around Eg: Neurospora crassa Map distance = ( ½ No of SDS Asci / T otal no of Asci ) 100

10. Life cycle of Neurospora

11. 1+2 3+4 5+6 7+8 No. of Asci 1 a + a + + b + b 79 2 a + + + a b + b 14 3 a + a b + + + b 6 4 a + + b a + + b 1 Spores Two strains of Neurospora , one mutant for gene a, the other mutant for gene b are crossed . Determine the linkage relationships b/w these to genes and the map distance

12. References 1.Daniel L. Hartl & Elizabeth W. Jones, 4 th edition 1998 Genetics: Principles and Analysis , Jones and Bartlett Publishers International, London UK. 2. Anthony J.F. Griffiths & Susan R. Wessler , 8 th Edition An Introduction to Genetic Analysis W.H . FREEMAN Publishers 3 . Williamd Stansfield , 3 rd Edition Schavm's outline of theory and problems Genetics, McGraw hill Publications, USA