1. Dihybrid Inheritance
Dihybrid inheritance refers to the simultaneous inheritance of two characters

2. Mendel’s experiment
Mendel investigated the inheritance of seed shape (round v wrinkled) and seed color (green v yellow) at the same time.
From his monohybrid crosses he knew that round seeds were dominant to wrinkled seeds and yellow seeds were dominant to green seeds.
He chose to cross plants that were pure breeding for both dominant features (round and yellow seeds) with plants that were pure breeding for both recessive features (wrinkled and green seeds)

3. Results
Parents plants with round x plants with wrinkled and yellow seeds and green seeds
F1 offspring 100% plants with round and yellow seeds
F1 intercross plants with round x plants with round
and yellow seeds and yellow seeds
F2 offspring Total 556 seeds collected from F2 plants
Ratio
round and yellow seeds
round and green seeds
wrinkled and yellow seeds
wrinkled and green seeds
However, the ratio of dominant to recessive features is still 3:1

4. Explanation of Mendel’s results
Let the allele for round seeds be R and the allele for wrinkled seeds be r
Let the allele for yellow seeds be Y and the allele for green seeds be y
Parents Phenotype round x wrinkled
yellow seeds green seeds
Genotype RR YY rryy
Gametes
F1 offspring RY RY ry ry

5. F1 intercross
Parents
phenotype round, yellow seeds x round, yellow seeds
genotype Rr Yy Rr Yy
Gametes RY Ry rY ry RY Ry rY ry
What are the genotypes and phenotypes of the F2 offspring and in what ratio?

6. F2 offspring genotypes phenotypes expected observed
RRYY (1) RrYy (4) yellow, round
RRYy (2) RrYY (2) yellow, round
RRyy (1) Rryy (2) round, green
rrYY (1) rrYy (2) wrinkled, yellow
rryy (1) wrinkled, green

7. Allowing for statistical error, Mendel’s results were a reasonable approximation to the expected 9:3:3:1 ratio
Each of a member of an allelic pair may combine randomly with either of another pair
A test cross can be performed to check the possible genotypes of a plant producing round, yellow seeds (RRYY, RrYY, RrYy, RRYy) by crossing the plants with a homozygous recessive plant with wrinkled green seeds genotype rryy
What phenotypes and genotypes would the offspring possess from the 4 crosses, and in what ratios?