Gregor Mendel’s
monastery garden.
Fig. 2.2
1
Removed stamens
from purple flower
2 Transferred sperm-
bearing pollen from
stamens of white
flower to eggbearing carpel of
purple flower
Parental
generation
(P)
3 Pollinated carpel
Stamens
Carpel (male)
(female)
matured into pod
4 Planted seeds
from pod
5 Examined
First
generation
offspring
(F1)
offspring:
all purple
flowers
Dominant
Recessive
X
X
X
X
X
X
EXPERIMENT True-breeding purple-flowered pea plants and
white-flowered pea plants were crossed (symbolized by ). The
resulting F1 hybrids were allowed to self-pollinate or were crosspollinated with other F1 hybrids. Flower color was then observed
in the F2 generation.
P Generation
(true-breeding
parents)

Purple
flowers
White
flowers
F1 Generation
(hybrids)
All plants had
purple flowers
RESULTS Both purple-flowered plants and whiteflowered plants appeared in the F2 generation. In Mendel’s
experiment, 705 plants had purple flowers, and 224 had white
flowers, a ratio of about 3 purple : 1 white.
F2 Generation
White
(pp)
Purple
(Pp)
Gametes
p
Purple
(PP)
p
P
Gametes
Gametes
Purple
(Pp)
P
p
PP
Pp
P
Pp
Pp
Gametes
p
P
Pp
Pp
F1 generation
All purple
Pp
pp
F2 generation
¾ purple, ¼ white
Parental P0 cross
P
P
p
p
F1 cross
P
P
p
Determine the genotype and phenotype
p
Parental P0 cross
p
p
P
Pp
Pp
P
Pp
Pp
F1 cross
P
p
P
PP
Pp
Determine the genotype and phenotype
p
Pp
pp
Phenotype
Purple
3
Purple
Genotype
PP
(homozygous)
1
Pp
(heterozygous)
2
Pp
(heterozygous)
Purple
1
Figure 14.6
White
pp
(homozygous)
Ratio 3:1
Ratio 1:2:1
1
copyright cmassengale
17
RrYy
RY Ry rY ry
x
RrYy
RY Ry rY ry
All possible gamete combinations
copyright cmassengale
18
RY
Ry
rY
ry
RY
Ry
rY
ry
copyright cmassengale
19
RY
RY RRYY
Ry
rY
ry
RRYy
RrYY
RrYy
Ry
rY
ry
RRYy
RrYY
RrYy
RRyy
RrYy
Rryy
RrYy
rrYY
rrYy
Rryy
rrYy
rryy
copyright cmassengale
Round/Yellow:
Round/green:
9
3
wrinkled/Yellow: 3
wrinkled/green:
1
9:3:3:1 phenotypic
20
ratio
LAW
DOMINANCE
SEGREGATION
INDEPENDENT
ASSORTMENT
PARENT
CROSS
OFFSPRING
TT x tt
tall x short
100% Tt
tall
Tt x Tt
tall x tall
75% tall
25% short
RrGg x RrGg
round & green
x
round & green
9/16
pods
3/16
pods
3/16
pods
1/16
pods
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round seeds & green
round seeds & yellow
wrinkled seeds & green
wrinkled seeds & yellow
21
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22
r
r
R
R
copyright cmassengale
23
r
r
R
Rr
Rr
R
Rr
Rr
produces the
F1 generation
All Rr = pink
(heterozygous pink)
copyright cmassengale
24
copyright cmassengale
25
copyright cmassengale
26
IA
i
IB
IAIB
IBi
IB
IAIB
IBi
copyright cmassengale
1/2 = IAIB
1/2 = IBi
27
• Example: male Type O (ii)
x
female type AB (IAIB)
IA
IB
i
IAi
IBi
i
IAi
IBi
copyright cmassengale
1/2 = IAi
1/2 = IBi
28
copyright cmassengale
29
Example: Eye color in fruit flies
Sex Chromosomes
fruit fly
eye color
XX chromosome - female
Xy chromosome - male
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30
Xr
Xr
XR
Y
copyright cmassengale
31
Xr
XR
XR
Xr
Y
Xr Y
Xr
XR
Xr
Xr Y
50% red eyed
female
50% white eyed
male
copyright cmassengale
32
copyright cmassengale
33
Genotypes could be:
SS or Ss for stars
What would the genotype for no
stars have to be?
R
r
R
RR
Rr
r
Rr
rr
R
r
R
RR
Rr
R
RR
Rr