Two Genes Unlinked Aa Bb x aa bb ABAbaBab abAaBbAabbaaBbaabb 1AB: 1Ab: 1aB: 1ab Two Genes Linked A...
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Transcript of Two Genes Unlinked Aa Bb x aa bb ABAbaBab abAaBbAabbaaBbaabb 1AB: 1Ab: 1aB: 1ab Two Genes Linked A...
Two GenesUnlinked
Aa Bb x aa bb
AB Ab aB ababAaBb AabbaaBbaabb
1AB: 1Ab: 1aB: 1ab
Two GenesLinked
A B/a b x ab/ab
AB abab AB/abab/ab
1AB: 1ab
Perform Test Crosses to Determine if Genes Are Linked
Prophase IPaired Homologous Chromosomes
(tetrad of 4 chromatids)
Chiasmata(Crossing-over points)
F yy ww x M y+ w+ Yyellow body, brown bodywhite eyes red eyes
P
F1
If genes independently assort1y+ w+ Y: 1y+ w Y: 1 y w+ Y: 1y w Ybrown body brown body yellow body yellow body
red eyes white eyes red eyes white eyes
F2
F y+y w+wbrown body
red eyes
M y w Yyellow bodywhite eyes
x
Actual Data4484 y+ w+ Y:4413 y w Y: 76 y w+ Y: 53y+ w Y
brown body yellow body yellow body brown bodyred eyes white eyes red eyes white eyes
“Parental Classes” “Recombinant Classes”4484 y+ w+ Y 76 y w+ Y
brown body, red eyes yellow body, red eyes
4413 y w Y 53 y+ w Y yellow body, white eyes brown body, white eyes
4484 + 4413 x 100 = 99% 76 + 53 x 100 = 1% 9026 9026
F yy ww x M y+ w+ Yyellow body, brown bodywhite eyes red 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 femalesGenerates the Recombinant Gametes
y+ w+ y+ w y w+
X
F2
F w+ m+/w+ m+ x M w m/Yred eyes, white eyes,wt wings miniature wings
P
F1 F w+ m+/w mred eyeswt wings
M w+ m+/Y red eyes wt wings
x
Parental: w+ m+/Y 412red eyes, wt wings
w m/Y 389white eyes, miniature wings
Recombinant: w+ m/Y 206red eyes, miniature wings
w m+/Y 185white eyes, wt wings
412+389 x 100= 67.2% 1192
206+185 x 100= 32.8% 1192
}
}
Fig. 4.4
F b c+/b c+ x M b+ c/b+ cblack body, wt body,
wt wings curved wingsP
F1 F b c+/b+ cwt body (b/b+)wt wings (c+/c)
M b c/b cblack body,
curved wings
x Test Cross!
Fig. 4.5
Crossing-Over in theF1 Female b c+/b+ c
b c+
b+ c
b c+
b c
b+ c
b+ c+
b c+
b c
b+ c+
b+ c
Prophase I Metaphase II Gametes
F2
F b c+/b c+ x M b+ c/b+ cblack body, wt body body,
wt wings curved wingsP
F1 F b c+/b+ cwt body (b/b+)wt wings (c+/c)
M b c/b cblack body,
curved wings
x Test Cross!
black body, wt wings 2934
black body, curved wings871
wt body, curved wings2768
wt body, wt wings 846
Parental: black body, wt wings 2934
Recombinant: black body, curved wings871
Parental: wt body, curved wings 2768
Recombinant: wt body, wt wings846
Parental: black body, wt wings 2934b c+/b c
Recombinant: black body, curved wings871b c/b c
Parental: wt body, curved wings 2768b+ c/b c
Recombinant: wt body, wt wings846b+ c+/b c
total=7419
% Recombination =(871 + 846)/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 Sety- w 1.1% Recombination Frequencyw-m 32.8% Recombination Frequencyy-m 34.3% Recombination Frequency
The First Chromosome Map
1.1 32.8
34.3
w-m 32.8
A Series of Two Point Crosses Can Generate A Chromosome Map
Fig. 4.11
Three Point Mapping Cross: Order of Genes Unknown
P ¡ vg b pr/vg b pr x ¢ vg+ b+ pr+/vg+ b+ pr+
vestigial wings wt wingsblack body wt bodypurple eyes wt eyes
F1 vg b pr/vg+ b+ pr+
all wildtype
Test Cross Heterozygous F1:¡ vg b pr/vg+ b+ pr+ x ¢ vg b pr/vg b pr
F2:vestigial, black, purple 1779
wildtype 1654
black, purple 252
vestigial 241
black 131
vestigial, purple 118
vestigial, black 13
purple 9
4197
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
Three Point Mapping Cross: Order of Genes Unknown
P ¡ vg b pr/vg b pr x ¢ vg+ b+ pr+/vg+ b+ pr+
vestigial wings wt wingsblack body wt bodypurple eyes wt eyes
F1 vg b pr/vg+ b+ pr+
all wildtype
Test Cross Heterozygous F1:¡ vg b pr/vg+ b+ pr+ x ¢ vg b pr/vg b pr
F2:vestigial, black, purple 1779
wildtype 1654
black, purple 252
vestigial 241
black 131
vestigial, purple 118
vestigial, black 13
purple 9
4197
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