dihybrid punnett squares
DESCRIPTION
Dihybrid Punnett Squares. What exactly is a dihybrid cross? Predicting the outcomes from crossing 2 traits. Why do we use them? Instead of doing to monohybrid crosses, you can combine them to see all the possible combinations from that particular mother and father. Dihybrid Cross. - PowerPoint PPT PresentationTRANSCRIPT
Dihybrid Punnett SquaresDihybrid Punnett SquaresWhat exactly is a dihybrid cross?
Predicting the outcomes from crossing 2 traits.
Why do we use them?Instead of doing to monohybrid
crosses, you can combine them to see all the possible combinations from that particular mother and father.
Dihybrid CrossDihybrid CrossTraits: Seed shape & Seed colorTraits: Seed shape & Seed colorAlleles:Alleles: R round r wrinkled Y yellow y green
RrYy x RrYy
RY Ry rY ryRY Ry rY ry RY Ry rY ryRY Ry rY ry
All possible gamete combinationsAll possible gamete combinations
Dihybrid CrossDihybrid Cross
RYRY RyRy rYrY ryry
RYRY
RyRy
rYrY
ryry
Dihybrid CrossDihybrid Cross
RRYY
RRYy
RrYY
RrYy
RRYy
RRyy
RrYy
Rryy
RrYY
RrYy
rrYY
rrYy
RrYy
Rryy
rrYy
rryy
Round/Yellow: 9
Round/green: 3
wrinkled/Yellow: 3
wrinkled/green: 1
9:3:3:1 phenotypic ratio
RY Ry rY ry
RY
Ry
rY
ry
Incomplete DominanceWhen the heterozygous condition
is intermediate between dominant and recessive
Happens because one allele is defective, example: R=red flowers, R’= white flowers so RR’ = pink flowers (R codes for enzyme to produce red pigment, R’=no enzyme)
Incomplete dominance
White
Red
F1 generation: 1 Red: 2 Pink: 1 white
RR x R’R’
R’R’ x R’R’
CodominanceCodominance
Heterozygote expresses both alleles’ conditionsEx. A black rooster bred with a
white hen produces a black and white checkered chicken.
Usually uses both capital letters (black= B, white=W , checkered = BW)
Codominance practice: cross a black rooster with a white hen
B
B
WW
Results:
100% checkered (BW)
BW BW
BW BW
Key:
B = black
W = white
BW = checkered
Now let’s cross a checkered hen with a checkered rooster.
B
W
WBResults:
25% Black
50% Checkered
25% White
(1:2:1)
BB BW
BW WW
CodominanceCodominance
Two allelesTwo alleles are expressed are expressed ((multiple allelesmultiple alleles) in ) in heterozygous heterozygous individualsindividuals..
Example:Example: blood type blood type
1.1. type Atype A = I= IAAIIAA or I or IAAii2.2. type Btype B = I= IBBIIBB or I or IBBii3.3. type ABtype AB= I= IAAIIBB
4.4. type Otype O = ii= ii
Blood type quick factsBlood type quick factsRed blood cells are called erythrocytes
Proteins on their surfaces are called antigens, controlled by genes
Antigens make antibodies to foreign substances, which includes RBCs with different antigens on their surface
4 phenotypes: A, B, AB, O3 alleles: IA, IB, i
• The lA allele is dominant to i, so
inheriting either the lAi alleles or the lA lA alleles from both parents will give
you type A blood.
Phenotype APhenotype A
• Surface molecule A is produced.
Surface molecule A
• The lB allele is also dominant to i.
Phenotype BPhenotype B
• To have type B blood, you must
inherit the lB allele from one parent and
either another lB allele or the i allele
from the other.
• Surface molecule B is produced.
Surface molecule B
• The lA and lB alleles are codominant.
Phenotype ABPhenotype AB
• If you inherit the lA allele from one parent and the lB allele from the other, your red
blood cells will produce both surface molecules and you will have type
AB blood.
Surface molecule B
Surface molecule A
Phenotype OPhenotype O
•No antigens produced
Blood Group
Antigens Antibodies Can receive
from
Can give to
A A B A or O A or AB
B B A B or O B or AB
AB A and B None A, B, AB, O
AB
O None both O A, B, AB, O
Codominance ProblemCodominance Problem
Example:homozygous male Type B (IBIB) x
heterozygous female Type A (IAi)
IAIB IBi
IAIB IBi
1/2 = IAIB
1/2 = IBi
IB
IA i
IB
Another Codominance Another Codominance ProblemProblem
Example:Example: male Type O (ii) x female type AB (IAIB)
IAi IBi
IAi IBi
1/2 = IAi1/2 = IBi
i
IA IB
i