A dihybrid cross is a breeding experiment between two organisms which are identical hybrids for two traits. In other words, a dihybrid cross is a cross between two organisms, with both being heterozygous for two different traits. The individuals in this type of trait are homozygous for a specific trait. These traits are determined by DNA . Dihybrid Cross Examples. Mendel took a pair of contradicting traits together for crossing, for example colour and the shape of seeds at a time. He chose the green wrinkled seed and round-yellow seed and crossed them. He obtained only round-yellow seeds in the F1 generation. This indicated that round shape and yellow colour of seeds are dominant. A dihybrid cross describes a mating experiment between two organisms that are identically hybrid for two traits. ... From his experiment, Mendel observed that the pairs of traits in the parental generation sorted independently from one another, from one generation to the next.

1. “Dihybrid cross is the cross between two different genes that differ in two observed traits.”
“Dihybrid cross”
Presented By:
Dr. R. N. CHAVHAN
Assistant Professor in Zoology,
Mahatma Gandhi Arts, science and
late N. P. Commerce college, Armori, District Gadchiroli (M.S.)

2. The inheritance of dihybrid traits can be calculated according to the following steps:
Step 5: Write out the phenotype ratios of potential offspring
 Phenotypic ratios reflect mathematical probabilities only and may not
necessarily reflect actual offspring ratios
Step 1: Designate characters to represent the alleles
 Capital letter for dominant allele, lower case letter for recessive allele
Step 2: Write down the genotype and phenotype of the parents (P generation)
 Always pair alleles from the same gene and always write capitals first (e.g. AaBb, not ABab)
Step 3: Write down all potential gamete combinations for both parents
 Use the FOIL method (or the claw) to identify all possible combinations
Step 4: Use a Punnett square to work out potential genotypes of offspring
 Only include the different gamete combinations for each parent (e.g.
AaBB has two combinations = AB and aB)
Genetic crosses involving two pairs of contrasting genetic characters are called dihybrid crosses

3. RY Ry rY ry
R r Y y
ONE PARENT OTHER PARENT
YELLOW SEED COLOUR (YY) DOMINANT GREEN SEED COLOUR (yy) RECESSIVE
ROUND SEED SHAPE (RR) DOMINANT WRINKED SEED SHAPE (rr) RECESSIVE
YELLOW = YY
ROUND = RR
GREEN = yy
WRINKLED = rr
SELF
FERTILIZATION
The plant having YYRR genotype is a pure
dominant, while that having the yyrr
genotype is a pure recessive.

4. Phenotypic Ratio:9:3:3:1

5. RRYY = 1
RRYy = 2
RrYY = 2
RrYy = 4
RRyy = 1
Rryy = 2
rrYY = 1
rrYy = 2
rryy = 1
Genotypic Ratio:
1: 2: 2: 4: 1: 2: 1: 2:
1