Download Multiple Alleles

Multiple Alleles
Multiple Alleles
• For each trait Mendel studied, there were
only two possible alleles. The dominant
allele controlled the trait. However, it is
possible to have more than two alleles,
this is called multiple alleles.
• Geneticists that study fruit flies (Drosophila
melanogaster), have seen many alleles for
one gene. They use numbers to indicate
which allele is dominant over another.
• In fruit flies the eye colors can be as
follows:
wild (E1E1), coral (E2E2), blood (E3E3),
easin (E4E4), cherry (E5E5), apricot (E6E6),
honey (E7E7), buff (E8E8), tinged (E9E9),
pearl (E10E10), ivory (E11E11), white
(E12E12)
* The smaller number is dominant over a
• E.g A fruit fly
heterozygous
wild/blood mates with
one heterozygous
coral/easin, describe
possible offspring eye
color.
• Parents: E1E3 * E2E4
F1
E1
E3
E2
E1E2
E2E3
E4
E1E4
E3E4
2 wild eye
1 coral eye
1 blood eye
Incomplete Dominance
• Prior to Mendel’s studies, scientists believed that
hybrids would have a blending of traits.
Although Mendel never found examples of this,
many do exist in nature.
• When Red x white = pink, this is called
intermediate inheritance (incomplete
dominance) .
• Another type of incomplete dominance is called
co-dominance, where both alleles are
expressed (Roan cows have red and white hair)
• This is a contradiction to Mendel’s thought that
one trait is always dominant over another
Law of Incomplete Dominance
• Both genes may be expressed
E.g. If a plant breeding pure for red flowers
crosses with one breeding pure for white
flowers. Red and white are incompletely
dominant producing pink flowers.
Describe possible F1 and F2 generation
offspring.
Pure red and pure white mate (F1)
• Parents RR x WW = RW
F1
R
R
W
RW
RW
W
RW
RW
Phenotype (what you see) – all pink
Pink and Pink mate (F2)
• Parents RW x RW
F1
R
W
R
RR
RW
W
RW
WW
Phenotype (what you see) –
1 red
2 pink
1 white
1. If a plant breeding pure for green leaf and
pure for purple flower crosses with one
breeding pure for white leaf and pure for
white flower (green + white are
incompletely dominant producing striped
leaf and purple and white are incompletely
dominant producing mauve flowers).
Describe possible F1 and F2 generation
offspring.
GG PP x WW FF
F2
GP
GP
WF
WGPF
WGPF
WF
WGPF
WGPF
G – green leaf
P - purple flower
W – white leaf
F – white flower
Phenotype –
100% are striped leaf and mauve
flower
Genotype –
100% WGPF
WG PF x WG PF
F2
WP
WF
GP
GF
WP
WW
PP
WW
PF
WG
PP
WG
PF
WF
GP
GF
WW WG
PF PP
WW WG
FF PF
WG
PF
WG
FF
WG
PF
WG
FF
GG
PF
GG
FF
GG
PP
GG
PF
Phenotype –
1 / 16 white seed, purple flower
2 / 16 white seed, mauve flower
1 / 16 white seed, white flower
2 / 16 striped seed, purple flower
4 / 16 striped seed, mauve flower
2 / 16 striped seed, white flower
1 / 16 green seed, purple flower
2 / 16 green seed, mauve flower
1 / 16 green seed, white flower
Genotype –
1 / 16 WW PP
2 / 16 WW PF
1 / 16 WW FF
2 / 16 WG PP
4 / 16 WG PF
2 / 16 WG FF
1 / 16 GG PP
2 / 16 GG PF
1 / 16 GG FF
• A guinea pig breeding pure for long hair
and pure for cowlicks mates with one
breeding pure for short hair and smooth
coat (Long hair and short hair are
incompletely dominant producing medium
length hair, while cowlicks are dominant.
• Describe possible F1 and F2 generation
offspring.
LL CC x SS cc
F2
LC
LC
Sc
LSCc
LSCc
Sc
LSCc
LSCc
L – Long hair
C - cowlicks
S – short hair
c – smooth hair
Phenotype –
100% are medium length with
cowlicks
Genotype –
100% LSCc
LSCc x LSCc
F2
LC
Lc
SC
Sc
LC
LL
CC
LL
Cc
LS
CC
LS
Cc
Lc
LL
Cc
LL
cc
LS
Cc
LS
cc
SC
Sc
LS
CC
LS
Cc
LS
Cc
LS
cc
SS
CC
SS
Cc
SS
Cc
SS
cc
Phenotype –
3 / 16 long hair, cowlick
1 / 16 long hair, smooth
6 / 16 medium hair, cowlick
1 / 16 medium hair, smooth
3 / 16 short hair, cowlick
1 / 16 short hair, smooth
Genotype –
1 / 16 LL CC
2 / 16 LL Cc
1 / 16 LL cc
2 / 16 LS CC
4 / 16 LS Cc
2 / 16 LS cc
1 / 16 SS CC
1 / 16 SS cc
2 / 16 SS Cc
• A plant breeding pure tall, pure red flowers
and pure green leaf, crosses with one pure
short, pure white flower and pure yellow
leaf. Underlined traits are dominant.
Describe phenotype of possible F1 and F2
generation offspring.
• Tri-hybrid cross
TT RR GG x tt rr gg
F2
TRG
TRG
trg
Tt Rr
Gg
Tt Rr Gg
trg
Tt Rr
Gg
Tt Rr Gg
Phenotype –
100% are tall with red flowers
and green leaves
Genotype –
100% Tt Rr Gg
T – tall , t – short
R – red flower, r – white flower
G – green leaf, g – yellow leaf
Tt Rr Gg x Tt Rr Gg
F2
TRG
TRG
trg
Tt Rr
Gg
Tt Rr Gg
trg
Tt Rr
Gg
Tt Rr Gg
Phenotype –
100% are tall
with red
flowers and
green leaves
Genotype –
100% Tt Rr Gg
T – tall , t – short
R – red flower, r – white flower
G – green leaf, g – yellow leaf