4/11/ 12Bell Ringer
1. What does incomplete dominance mean?
2. If I had a Red Homozygous Flower and a White Homozygous Flower, what would the Heterozygous Flower look like in incomplete dominance?
3. If I had a Dark Brown Homozygous Horse and a White Homozygous Horse, what would the Heterozygous Horse look like in incomplete dominance?
Incomplete Dominance
oWhen one allele is not completely dominant over another.
oHeterozygous phenotype is between the two homozygous phenotypes.
Homozygous Heterozygous Homozygous
RR R’R’
RR
R’
R’
RR’
RR’RR’
RR’
x
Now you try one
A Heterozygous snapdragon flower is crossed with another Heterozygous
snapdragon flower. What Genotypes and Phenotypes could the offspring
potentially have?
x
RR’ RR’
R
R R’
R’
R R
R’ R’R R’
R R’
25% RR50% R R’25% R’ R’
25% Red50% Pink25% White
Codominance
oWhen two dominant alleles are expressed at the same time.
o The phenotypes of both homozygotes are produced in heterozygotes.
x
BB WW
B B
W
W BWBW
BWBW
Now you try one
A Heterozygous Chicken is crossed with a Homozygous White Chicken. What
Genotypes and Phenotypes could the offspring potentially have?
WWBW
W W
B
W WWWW
BWBW
50% BW50% WW
50% Checkered50% White
Multiple Alleles
o Some traits can have multiple alleles that control what phenotype an organism will have.
B
A= Dominant
B
= Dominant to b but recessive to B A
b
= Recessive to both of the other alleles
Multiple Alleles In Humans
BLOOD TYPING:Single gene that has multiple alleles
O
A B
AB
How is a person’s blood type determined?
oBy the presence or absence of large molecules (Antigens) on the red blood cells.
o Antibodies (part of our immune system) react with foreign antigens so it is important for doctors to know their patients blood type.
ABO Blood GroupHUMAN BLOOD TYPES
PHENOTYPE GENOTYPE
A AA or AO
B BB or BO
AB AB
O OO
There are 3 alleles for blood typeA, B, and O
HUMAN BLOOD TYPES
PHENOTYPE GENOTYPE
A AA or AO
B BB or BO
AB AB
O OO
A is dominant to OB is dominant to O
A and B are Codominant
There are 3 alleles for blood type:A, B, and O
A B O
A AA AB AO
B AB BB BO
O AO BO OO
How many different allele combinations are there for Blood Type?
A person with the blood type AA is crossed with a person with the
blood type BB. What blood types could their offspring have?
A A
BB
ABABAB AB
One parent has the blood type A and the other blood type B. What are the
genotypes of the parents if they produce children with only blood type
AB?
Parents Phenotype
Parents Genotype Type A
Type B
or
or
A A A O
B B B O
A A
B
B
ABAB
AB AB
A A
O
B
AOAO
AB AB
A O
B
B
BOAB
AB BO
A O
O
B
OOAO
AB BO
