P Generation Yellow-round seeds (YYRR) Y F 1 Generation Y R R R Y r r r y y y Meiosis Fertilization Gametes Green-wrinkled seeds ( yyrr) All F 1 plants produce yellow-round seeds (YyRr) R R Y Y r r y y Meiosis R R Y Y r r y y Metaphase I Y Y R R r r y y Anaphase I r r y Y Metaphase II R Y R y y y y R R Y Y r r r r y Y Y R R yR Yr yr YR 1 / 4 1 / 4 1 / 4 1 / 4 F 2 Generation Gametes An F 1 F 1 cross-fertilization 9 : 3 : 3 : 1 LAW OF INDEPENDENT ASSORTMENT Alleles of genes on nonhomologous chromosomes assort independently during gamete formation. LAW OF SEGREGATION The two alleles for each gene separate during gamete formation. 1 2 3 3 2 1 1
P Generation. Yellow-round seeds ( YYRR ). Green-wrinkled seeds ( yyrr ). y. Y. r. . R. r. R. Y. y. Meiosis. Fertilization. r. y. Y. R. Gametes. All F 1 plants produce yellow-round seeds ( YyRr ). F 1 Generation. R. R. y. y. r. r. Y. Y. LAW OF SEGREGATION - PowerPoint PPT Presentation
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P Generation Yellow-roundseeds (YYRR)
Y
F1 Generation
Y
R R
R Y
r
r
r
y
y
y
Meiosis
Fertilization
Gametes
Green-wrinkledseeds ( yyrr)
All F1 plants produceyellow-round seeds (YyRr)
R R
YY
r ry y
Meiosis
R R
Y Y
r r
y y
Metaphase I
Y Y
R Rrr
y y
Anaphase I
r r
y Y
Metaphase IIR
Y
R
y
yyy
RR
YY
rrrr
yYY
R R
yRYryrYR1/41/4
1/41/4
F2 Generation
Gametes
An F1 F1 cross-fertilization
9 : 3 : 3 : 1
LAW OF INDEPENDENTASSORTMENT Alleles of geneson nonhomologouschromosomes assortindependently during gameteformation.
LAW OF SEGREGATIONThe two alleles for each geneseparate during gameteformation.
1
2
33
2
1
1
Parent
Bud
0.5 mm
2
PGeneration
Generation
Generation
Generation
Generation
Generation
F1
F2
All offspring had red eyes
Sperm
EggsF1
F2
P
Sperm
Eggs
XX
XY
CONCLUSION
EXPERIMENT
RESULTS
w
w
w
w
ww
w w
+
+
++ +
w
ww w
w
w
w
ww
+
+
+
+ +
+
3
X
Y
4
44 + XY
Parents 44 + XX
22 + X
22 +X
22 + Yor +
44 + XX or
Sperm Egg
44 + XY
Zygotes (offspring)
(a) The X-Y system
22 + XX
22 + X
(b) The X-0 system
76 + ZW
76 + ZZ
(c) The Z-W system
32(Diploid)
16(Haploid)
(d) The haplo-diploid system
5
(a) (b) (c)
XNXN XnY XNXn XNY XNXn XnY
YXnSpermYXNSpermYXnSperm
XNXnEggs XN
XN XNXn
XNY
XNY
Eggs XN
Xn
XNXN
XnXN
XNY
XnY
Eggs XN
Xn
XNXn
XnXn
XNY
XnY
6
X chromosomes
Early embryo:
Allele fororange fur
Allele forblack fur
Cell division andX chromosomeinactivationTwo cell
populationsin adult cat:
Active XActive X
Inactive X
Black fur Orange fur
7
EXPERIMENTP Generation (homozygous)
RESULTS
Wild type(gray body,normal wings)
Double mutant(black body,vestigial wings)
b b vg vg
b b vg vg
Double mutantTESTCROSS
b+ b+ vg+ vg+
F1 dihybrid(wild type)
b+ b vg+ vg
Testcrossoffspring Eggs b+ vg+ b vg b+ vg b vg+
Black-normal
Gray-vestigial
Black-vestigial
Wild type(gray-normal)
b vg
Sperm
b+ b vg+ vg b b vg vg b+ b vg vg b b vg+ vg
PREDICTED RATIOS
If genes are located on different chromosomes:
If genes are located on the same chromosome andparental alleles are always inherited together:
1
1
1
1
1 1
0 0
965 944 206 185
:
:
:
:
:
:
:
:
:
8
Testcrossparents
Replicationof chromo-somes
Gray body, normal wings(F1 dihybrid)
Black body, vestigial wings(double mutant)
Replicationof chromo-somes
b+ vg+
b+ vg+
b+ vg+
b vg
b vg
b vg
b vg
b vg
b vg
b vgb vg
b vg
b+ vg+
b+ vg
b vg+
b vg
Recombinantchromosomes
Meiosis I and II
Meiosis I
Meiosis II
b vg+b+ vgb vgb+ vg+
Eggs
Testcrossoffspring
965Wild type
(gray-normal)
944Black-
vestigial
206Gray-
vestigial
185Black-normal
b+ vg+
b vg b vg
b vg b+ vg
b vg b vg
b vg+
Sperm
b vg
Parental-type offspring Recombinant offspring
Recombinationfrequency =
391 recombinants2,300 total offspring
100 = 17%
9
RESULTS
Recombinationfrequencies
Chromosome
9% 9.5%
17%
b cn vg
10
Mutant phenotypes
Shortaristae
Blackbody
Cinnabareyes
Vestigialwings
Browneyes
Redeyes
Normalwings
Redeyes
Graybody
Long aristae(appendageson head)
Wild-type phenotypes
0 48.5 57.5 67.0 104.5
11
Meiosis I
Nondisjunction
(a) Nondisjunction of homologous chromosomes in meiosis I
(b) Nondisjunction of sister chromatids in meiosis II