Dihybrid CrossProblem 3: A genetic cross yielding a 9:3:3:1 ratio of offspring.Tutorial to help answer the questionWhich of the following genetic crosses would be predicted to give a phenotypic ratio of 9:3:3:1?TutorialPredicting the genotype of offspringDetermine 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 9:3:3:1A 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
