Transcript Incomplete Dominance Codominance Multiple Alleles

Incomplete Dominance
Codominance
Multiple Alleles
Review
• Purple Flowers are dominant to White
Flowers
• Genotypes: ___________________
• Phenotypes: __________________
Review: Dominant/Recessive
• Fill-In: The stronger gene or ___________
gene will always mask the weaker gene or
_____________ gene
PP = purple
pp = white
Pp = purple
Review Problem:
Dominant/Recessive
• In pea plants, purple flowers (P) are dominant
over white flowers (p) show the cross between
two heterozygous plants.
GENOTYPES:
- PP (1); Pp (2); pp (1)
- ratio 1:2:1
PHENOTYPES:
- purple (3); white (1)
- ratio 3:1
P
p
P
PP
Pp
p
Pp
pp
Incomplete Dominance
• What if you did not have completely
dominant or completely recessive genes?
What if the traits were equally strong?
• This is incomplete dominance
• The two traits will combine or blend to
produce a third trait.
• In humans eye and hair color is decided
this way.
Incomplete Dominance
• A third (new) phenotype appears in the
heterozygous condition.
• Flower Color in 4 O’clocks
RR = red
rr = white
Rr = pink
Problem: Incomplete
Dominance
• Show the cross between a pink and a
white flower.
GENOTYPES:
- Rr (2); rr (2)
- ratio 1:1
r
Rr
rr
PHENOTYPES:
- pink (2); white (2)
- ratio 1:1
r
Rr
rr
R
r
Codominance
• The heterozygous condition, both
alleles are expressed equally
• Sickle Cell Anemia in Humans
NN =
normal cells
SS = sickle cells NS = some of
each
Problem: Codominance
• Show the cross between an individual with
sickle-cell anemia and another who is a
carrier but not sick.
N
S
GENOTYPES:
- NS (2) SS (2)
- ratio 1:1
S
NS
SS
PHENOTYPES:
- carrier (2); sick (2)
- ratio 1:1
S
NS
SS
Multiple Alleles
• Some genes have more than two alleles.
• One of the best-known examples is the gene that
is referred to as the “ABO Blood Group,” which
actually has quite a number of alleles.
• The three alleles we will work with are symbolized
by IA, IB, and i.
• However, keep in mind that a person can only
have two alleles, two copies of a gene. Thus, the
possible genotypes are IAIA, IAi, IBIB, IBi, IAIB, or ii.
• (Sometimes, you will see these simplified as AA,
AO, BB, BO, AB, and OO, but that does make it
harder to remember that these are all alleles for
the same gene.)
Who is a Donor?
• http://www.redcrossblood.org/learn-aboutblood/blood-types
Rules for Blood Type
• A and B are codominant
– AA = Type A
– BB = Type B
– AB = Type AB
• A and B are dominant over O
– AO = type A
– BO = type B
– OO = type O
Problem: Multiple Alleles
• Show the cross between a mother who has
type O blood and a father who has type AB
blood.
O
O
GENOTYPES:
- AO (2) BO (2)
- ratio 1:1
A
AO
AO
PHENOTYPES:
- type A (2); type B (2)
- ratio 1:1
B
BO
BO
Problem: Multiple Alleles
• Show the cross between a mother who is
heterozygous for type B blood and a father who is
heterozygous for type A blood.
GENOTYPES:
-AB (1); BO (1);
AO (1); OO (1)
- ratio 1:1:1:1
PHENOTYPES:
-type AB (1); type B (1)
type A (1); type O (1)
- ratio 1:1:1:1
A
O
B
AB
BO
O
AO
OO
In the 1950’s, a young woman sued film
star/director Charlie Chaplin for parental support of
her illegitimate child. Charlie Chaplin’s blood type
was already on record as type AB. The mother of
the child had type A and her son had type O blood.
• Complete a Punnett square for
the possible cross of Charlie and
the mother.
• The judge ruled in favor of the
mother and ordered Charlie
Chaplin to pay child support
costs of the child. Was the judge
correct in his decision based on
blood typing evidence?
• Explain why or why not.