Two Genes Unlinked Aa Bb x aa bb ABAbaBab abAaBbAabbaaBbaabb 1AB: 1Ab: 1aB: 1ab Two Genes Linked A B/a b x ab/ab ABab abAB/abab/ab 1AB: 1ab Perform Test Crosses to Determine if Genes Are Linked

Prophase I Paired Homologous Chromosomes (tetrad of 4 chromatids) Chiasmata (Crossing-over points)

F yy ww x M y+ w+ Y yellow body, brown body white eyesred eyes P F1 If genes independently assort 1y + w + Y:1y + w Y:1 y w + Y:1y w Y brown bodybrown bodyyellow bodyyellow body red eyeswhite eyesred eyeswhite eyes F2 F y + y w + w brown body red eyes M y w Y yellow body white eyes x Actual Data 4484 y + w + Y:4413 y w Y:76 y w + Y:53y + w Y brown bodyyellow bodyyellow bodybrown body red eyeswhite eyesred eyeswhite eyes

“Parental Classes”“Recombinant Classes” 4484 y + w + Y76 y w + Y brown body, red eyes yellow body, red eyes 4413 y w Y53 y + w Y yellow body, white eyes brown body, white eyes x 100 = 99% x 100 = 1% F yy ww x M y + w + Y yellow body, brown body white eyesred eyes P F2: F y + y w + w x M y w Y brown body, red eyes F1

y w Crossing Over in the F1 females Generates the Recombinant Gametes y + w + y + wy w + X

F2 F w + m + /w + m + x M w m/Y red eyes, white eyes, wt wingsminiature wings P F1 F w + m + /w m red eyes wt wings M w + m + /Y red eyes wt wings x Parental:w + m + /Y412 red eyes, wt wings w m/Y389 white eyes, miniature wings Recombinant: w + m/Y206 red eyes, miniature wings w m + /Y185 white eyes, wt wings x 100= 67.2% x 100= 32.8% 1192 } } Fig. 4.4

F b c + /b c + x M b + c/b + c black body, wt body, wt wingscurved wings P F1 F b c + /b + c wt body (b/b + ) wt wings (c + /c) M b c/b c black body, curved wings x Test Cross! Fig. 4.5

Crossing-Over in the F1 Female b c + /b + c bc+c+ b+b+ c bc+c+ bc b+b+ c b+b+ c+c+ bc+c+ bc b+b+ c+c+ b+b+ c Prophase IMetaphase IIGametes

F2 F b c + /b c + x M b + c/b + c black body, wt body body, wt wingscurved wings P F1 F b c + /b + c wt body (b/b + ) wt wings (c + /c) M b c/b c black body, curved wings x Test Cross! black body, wt wings2934 black body, curved wings871 wt body, curved wings2768 wt body, wt wings846 Parental: black body, wt wings2934 Recombinant: black body, curved wings871 Parental: wt body, curved wings2768 Recombinant: wt body, wt wings846 Parental: black body, wt wings2934 b c+/b c Recombinant: black body, curved wings871 b c/b c Parental: wt body, curved wings2768 b+ c/b c Recombinant: wt body, wt wings846 b+ c+/b c total=7419 % Recombination = ( )/7419 x 100 = 23% Fig. 4.5

Recombination Frequency Reflects Distances between Genes if closely linked: cross-overs less likely to occur between A&B if farther apart: cross-overs more likely to occur between A&B

Sturtevant’s Data Set y- w 1.1% Recombination Frequency w-m32.8% Recombination Frequency y-m34.3% Recombination Frequency The First Chromosome Map

w-m 32.8 A Series of Two Point Crosses Can Generate A Chromosome Map Fig. 4.11

vg b pr vg + b + pr + vg + b pr vg b + pr + vg + b pr + vg b + pr vg b pr + vg + b + pr F F M M Fig. 4.12

vg b pr vg + b + pr + vg b + pr vg + b pr + vestigial, purple black b vg pr b + vg + pr+ b vg + pr b + vg pr+ black, purple vestigial vg pr b vg + pr + b + vg pr + b vg + pr b + vestigial, black purple

vg b pr vg + b + pr + vg + b pr vg b + pr + vg + b pr + vg b + pr vg b pr + vg + b + pr F F M M Fig. 4.12