Is it possible to make 3:7ratio in dihybrid cross??
Answers
Answer:
Predicting the genotype of offspring
Determine all possible combinations of alleles in the gametes for each parent.
Half of the gametes get a dominant S and a dominant Y allele; the other half of the gametes get a recessive s and a recessive y allele.
Both parents produce 25% each of SY, Sy, sY, and sy.
(Review the tutorials for problems #1 and problem #4 if necessary).

Punnett square.
Since each Parent produces 4 different combinations of alleles in the gametes, draw a 4 square by 4 square punnett square.

Gametes from Parent 1
List the gametes for Parent 1 along one edge of the punnett square.

Gametes from Parent 2
List the gametes for Parent 2 along one edge of the punnett square.

Alleles from Parent 1
Fill out the squares with the alleles of Parent 1.

Alleles from Parent 2
Fill out the squares with the alleles from Parent 2.
The result is the prediction of all possible combinations of genotypes for the offspring of the dihybrid cross, SsYy x SsYy.

Predicting the phenotype of offspring
Spherical, yellow phenotype
There are 9 genotypes for spherical, yellow seeded plants. They are:
SSYY (1/16)
SSYy (2/16)
SsYY (2/16)
SsYy (4/16)

Spherical, green phenotype
Two recessive alleles result in green seeded plants.
There are 2 genotypes for spherical, green seeded plants. They are:
SSyy (1/16)
Ssyy (2/16)

Dented, yellow phenotype
Two recessive s alleles result in dented seeded plants.
There are 2 genotypes for dented, yellow seeded plants. They are:
ssYY (1/16)
ssYy (2/16)

Dented, green phenotype
A ssyy plant would be recessive for both traits.
There is only 1 genotypes for dented, green seeded plants. It is:
ssyy (1/16)

A phenotypic ratio of 9:3:3:1
A phenotypic ratio of 9:3:3:1 is predicted for the offspring of a SsYy x SsYy dihybrid cross.
9 spherical, yellow
3 spherical, green
3 dented, yellow
1 dented, green