TETRAD ANALYSIS IN FUNGI Image removed to due to copyright considerations THE PRODUCTS OF A SINGLE MEIOSIS ARE PACKAGED IN A SAC ASCUS THE PRODUCTS OF A SINGLE MEIOSIS Haploid Diploid 1st division Meiosis A a X A a A A a a A A a a Image A removed to due to a copyright a considerations A 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 HOW DO WE KNOW WHETHER TWO GENES ARE LINKED A B A A a a X B B b b AB AB a b a b Parental Ditype PD or a b b b B B A A a a Ab Ab a B a B Non Parental Ditype NPD How do you determine linkage You cross AB x ab and find in 100 tetrads 48 PD 52 NPD Are A and B linked 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 NPD Yes Two genes are unlinked No Two genes are linked Independent Assortment linkage AB x ab Tetradspeak Are PD NPD Two genes are unlinked Two genes are linked Complete Linkage of Two Genes X AB ab AB AB ab ab AB Parental ditype AB AB ab ab AB ab ab The Products of a Single Crossover A B a X A B A a a X b AB Parental B Ab b aB b ab Recombinant Recombinant Parental TETRATYPE 2 Independent Assortment linkage AB x ab Tetradspeak Are PD NPD Yes No Two genes are unlinked Two genes are linked TETRATYPE Yes Map Distance centiMorgans NO 100 linked 1 2 TT TOTAL How do you determine linkage You cross AB x ab and find in 100 tetrads 90 PD 10 TT Are they linked 90 PD 90 X4 360 Non Recombinant Progeny 10 TT 10 x 2 20 Recombinant Progeny MD in centimorgans Recombinants X 100 Total tetrads MD 20 400 5 centiMorgans Map Distance 1 2 TT centiMorgans TOTAL Linkage AB x ab Are PD NPD Yes Two genes are unlinked No Two genes are linked TETRATYPE Yes Map Distance 1 2 TT NO 100 linked TOTAL WHAT ABOUT DOUBLE CROSSOVERS DOUBLE CROSSOVERS A B AB A B A B AB A B Ab b ab b ab b aB a XX b A B Ab A B AB b aB a X b a ab a a PD ab X a TT AB A B A B Ab b aB b aB a X a 1PD 1NPD 2TT TT Ab NPD CROSSING OVER OCCURS AT THE 4 STRAND STAGE A B AB A B A B AB A B Ab b ab b ab b aB a XX b A B Ab A B AB b aB a X b a ab a a PD ab X a TT AB A B A B Ab b aB b aB a a X TT Ab NPD Linkage AB x ab Are PD NPD Yes No Two genes are linked TETRATYPE Two genes are unlinked Map Distance Yes NO 1 2 TT TOTAL 100 linked NPD NO YES SINGLE DOUBLE MD 1 2 TT 3NPD TOTAL ESTIMATION OF DOUBLE CROSSOVERS Singles TT Doubles 1PD 2TT 1NPD Single 1 2 TT 2NPD Doubles 4NPD MD 1 2 TT 2NPD 4NPD Total SINGLE DOUBLE MD 1 2 TT 3NPD TOTAL How do you determine linkage You cross AB x ab and find in 100 tetrads 70 PD 20TT 10NPD Count crossover gametes 40 4 10 X 100 20 cM 400 Analyze tetrads 10 30 100 X 100 40 cM If we just count crossover gametes we would underestimate the distance THE THREE TYPES OF TETRADS Parental AB AB a b a b Non Parental Ab Ab a B a B Tetratype AB Ab a B a b NO ONE TETRAD TYPE IS SUFFICIENT IT IS THE RELATIONSHIP THAT TELLS ALL
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