Dihybrid Crosses Incomplete Dominance Codominance Multiple Alleles In a nutshell!
Codominance When there are at least 2 usually 3 alleles that influence a trait. –1 is recessive....
24
Codominance •When there are at least 2 usually 3 alleles that influence a trait. –1 is recessive. –The other 2 are dominant to that allele but not to each other.
-
Upload
abigail-chambers -
Category
Documents
-
view
213 -
download
0
Transcript of Codominance When there are at least 2 usually 3 alleles that influence a trait. –1 is recessive....
Codominance•When there are at least 2 usually 3 alleles that influence a trait.
–1 is recessive. –The other 2 are dominant to that allele but not to each other.
Human
Blood Types
In the human population, there are 3 major alleles for the surface protein gene: A, B, and O.
A
B
O
A and B are dominant to O but not to each other
Recessive
Genotype Phenotype
AA or AO
IAIA or IAi
Type A
BB or BO
IBIB or IBi
Type B
AB
IAIB
Type AB
OO
ii
Type O
Human Blood Types
CodominanceCodominance
• Example:Example: homozygous male B (IBIB)
x heterozygous female A
(IAi)
IAIB IAIB
IBi IBi
1/2 = IAIB
1/2 = IBi
IA
IB IB
i
CodominanceCodominance
• Example:Example: male O (ii) x female AB (IAIB)
IAi IBi
IAi IBi
1/2 = IAi1/2 = IBi
i
IA IB
i
Codominance
• In codominance, the alleles are neither dominant, nor recessive. Neither allele is masked by the other.
Roan CowIs both white and red
Chestnut or Red Roan
Black or Blue Roan
Palonimo
Mystery Bull Experiment
• http://tepserver.ucsd.edu/people/Tracee-Parsons/Final-genetics-project/mystery-bull.html
Through genetic engineering, you and your partner, Maisie have developed a new type of corn. You have named it WonderCorn.
•It has a tasty flavor of butter and salt. •The good thing about this new corn is that you do not have to add butter and salt to it once it is cooked. •This makes it a much healthier dish.
Flav-R-Gro, Inc.
You and Maisie suspect that the taste trait is corn in codominant. To find out, you crossed two other types of corn: a homozygous salty corn (SS) and a homozygous buttery corn (BB). The offspring were all WonderCorn.
Create the Punnett Square
S S
B
B
SB SB
SB SB
What is the genotype of WonderCorn?
What percent of the offspring will have this genotype?
S B
S
B
You were correct. Taste is a codominant trait.
Make a Punnett Square showing a second-generation cross. (Both parents are heterozygous)
What percent of the offspring will be WonderCorn?
SS SB
SB BB
50 % will be WonderCorn.
1:2:1 Ratio
The demand for WonderCorn is high. Grover’s Grocery has already ordered 50 bushels and wants more. You are all out. You are at the beginning of a new growing season. Would you be better off using homozygous plants to grow or heterozygous? Why?
Do the math!
• If a heterozygous cross produces 736 offspring, how many will be WonderCorn?
• How many of the 736 offspring will taste salty but not buttery?
50% of 736 = 368 25% of 736 = 184
Quiz
Tomorrow
