Presentation on theme: "TETRAD ANALYSIS IN FUNGI"— Presentation transcript:
1 TETRAD ANALYSIS IN FUNGI Image removed to due to copyright considerations.THE PRODUCTS OF A SINGLE MEIOSISARE PACKAGED IN A SAC (ASCUS)
2 THE PRODUCTS OF A SINGLE MEIOSIS HaploidDiploid1stDivisionMeiosisImage removed to due tocopyright considerations.
3 Mendel 1.Segregation: Equal numbers of A and a The phenotype resulting from a mutation in a single gene will segregate exactly 2A : 2a.Question in Tetradspeak: Does the phenotype segregate2:2?Yes. A and a are alleles of a single gene.
4 HOW DO WE KNOW WHETHER TWO GENES ARE LINKED? ParentalDitype(PD)Non-ParentalDitype(NPD)
5 How do you determine linkage? You cross AB x ab and find in 100 tetrads:48 PD52 NPDAre A and B linked?
6 Mendel 1. Segregation: Equal numbers of A and a * The phenotype resulting from a mutation in a single gene will segregate exactly 2A : 2a.* Question in Tetradspeak:Does the phenotype segregate 2:2?Yes. A and a are alleles of a single gene.2. Independent Assortment (linkage): AB x ab* Tetradspeak: Are PD = NPDYesNoTwo genes are unlinkedTwo genes are linked
7 Independent Assortment (linkage): AB x ab *Tetradspeak: Are PD = NPD Two genes are unlinkedTwo genes are linked
9 The Products of a Single Crossover ParentalRecombinantRecombinantParentalTETRATYPE
10 •Tetradspeak: Are PD = NPD 2. Independent Assortment (linkage): AB x ab•Tetradspeak: Are PD = NPDYes NoTwo genes are linkedTETRATYPE?Two genes are unlinkedYes NO1/2 TTMap Distance100% linked=centiMorgansTOTAL
11 How do you determine linkage? You cross AB x ab and find in 100 tetrads:90 PD10 TTAre they linked?90 PD = 90 X4 = 360 Non-Recombinant Progeny10 TT = 10 x 2 = 20 Recombinant ProgenyMD in centimorgans = RecombinantsTotal tetradsMD = 20/400= 5 centiMorgansX 100Map DistancecentiMorgans=1/2 TTTOTAL
12 WHAT ABOUT DOUBLE CROSSOVERS? Linkage AB x abAre PD = NPD?Yes NoTwo genes are linkedTETRATYPE?Two genes are unlinkedYesNo1/2 TT=100% linkedMap DistanceTOTALWHAT ABOUT DOUBLE CROSSOVERS?
17 How do you determine linkage? You cross AB x ab and find in 100 tetrads:70 PD20TT10NPD(10)Count crossover gametes =X 100 = 20 cM400Analyze tetrads =X 100 = 40 cM100If we just count crossover gametes we would underestimate the distance.
18 THE THREE TYPES OF TETRADS ParentalNon-ParentalTetratypeNO ONE TETRAD TYPE IS SUFFICIENT.IT IS THE RELATIONSHIP THAT TELLS ALL
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