7.1.2 Dihybrid Inheritance

• In a dihybrid cross, the typical phenotypic ratio for heterozygous parents (YyRr) is 9:3:3:1
• The probability of the YYRR genotype in a dihybrid cross with heterozygous parents (YyRr) is 1/16
• The typical phenotypic ratio in a dihybrid cross arises from the independent assortment of alleles during gamete formation.
• Steps to analyze a dihybrid cross using a Punnett square.

  1️⃣ Identify the genes and genotypes of the parents

  2️⃣ Determine the possible gametes each parent can produce

  3️⃣ Create a 4x4 Punnett square

  4️⃣ Combine gametes to determine offspring genotypes

  5️⃣ Calculate the phenotypic ratio
• The first step in using a Punnett square for a dihybrid cross is to identify the genes and genotypes
• In a dihybrid cross with heterozygous parents, the 9:3:3:1 phenotypic ratio is a direct result of Mendel's Law of Independent Assortment.


  True
• Heterozygous parents in a dihybrid cross always produce a phenotypic ratio of 9:3:3:1.


  True
• If both parents are heterozygous dihybrids (YyRr), what is the probability of offspring being green and wrinkled?

  1/16
• What is the probability of the YYRR genotype in a dihybrid cross?

  6.25%
• What is the probability of offspring being dominant for both traits in a dihybrid cross?

  9/16
• Monohybrid crosses produce a phenotypic ratio of 9:3:3:1.

  False
• What is dihybrid inheritance?

  Inheritance of two genes
• What are the four types of gametes produced by a heterozygous dihybrid plant with genotype YyRr?

  YR, Yr, yR, yr
• What phenotypic ratio is observed in the offspring of a dihybrid cross?

  9:3:3:1
• In a dihybrid cross, the phenotypic ratio for dominant traits is 9:3:3:1.


  True
• What gametes can a heterozygous dihybrid (YyRr) produce?

  YR, Yr, yR, yr
• Which ratio arises from the independent assortment of two genes in a dihybrid cross?

  9:3:3:1
• The 9:3:3:1 phenotypic ratio represents the four possible combinations of the two dominant traits
• A dihybrid cross with heterozygous parents (YyRr) results in a 9:3:3:1 phenotypic ratio.


  True
• In a dihybrid cross, the phenotypic ratio for dominant traits is 9:3:3:1.


  True
• Dihybrid inheritance involves genes located on the same chromosome.

  False
• During gamete formation, the alleles for each gene segregate independently
• Steps to use Punnett squares for dihybrid crosses

  1️⃣ Identify the Genes and Genotypes

  2️⃣ Determine Gametes

  3️⃣ Set Up Punnett Square

  4️⃣ Fill in the Table

  5️⃣ Calculate Phenotypic Ratio
• Dihybrid inheritance is the inheritance of two genes located on different chromosomes
• In a dihybrid cross, the 9:3:3:1 phenotypic ratio arises from the independent assortment of two genes during gamete formation.


  True
• Match the gamete with its genotype in a dihybrid cross involving YyRr heterozygous parents:

  YR ↔️ Dominant for both traits

  Yr ↔️ Dominant for one, recessive for the other

  yR ↔️ Recessive for one, dominant for the other

  yr ↔️ Recessive for both traits
• The genotypic ratio in a dihybrid cross with heterozygous parents (YyRr) is 1:2:2:4:1:2:1:2:1.

  True
• Order the phenotypes in a 9:3:3:1 ratio for a dihybrid cross:

  1️⃣ Yellow, Round

  2️⃣ Yellow, Wrinkled

  3️⃣ Green, Round

  4️⃣ Green, Wrinkled
• Match the phenotype with its probability in a dihybrid cross with heterozygous parents (YyRr):

  Dominant for both traits ↔️ 9/16

  Dominant for one, recessive for the other ↔️ 3/16

  Recessive for both traits ↔️ 1/16
• Dihybrid inheritance involves two genes located on different chromosomes.


  True
• The 9:3:3:1 phenotypic ratio in a dihybrid cross arises from the random combination of gametes.


  True
• Genotype ratios in dihybrid crosses are visualized using a Punnett square.
• The typical phenotypic ratio in a dihybrid cross is dictated by Mendel's Law of Independent Assortment
• What is the probability of offspring being recessive for one trait and dominant for the other in a dihybrid cross with heterozygous parents?

  3/16
• Steps to analyze the probability of specific genotypes in dihybrid crosses

  1️⃣ Use a Punnett square

  2️⃣ Identify possible genotypes

  3️⃣ Calculate the ratio of each genotype

  4️⃣ Convert the ratio to a probability
• What is the total number of possible genotypes in a dihybrid cross using a Punnett square?

  16
• Dihybrid crosses follow Mendel's Law of Independent Assortment
• In tomatoes, if a plant heterozygous for both traits (RrTt) is crossed with a plant homozygous recessive for both (rrtt), what is the expected phenotypic ratio of the offspring?

  1:1:1:1
• Mendel's Law of Independent Assortment states that the inheritance of one gene is independent of the inheritance of another gene if they are located on different chromosomes
• During gamete formation, the alleles for each gene segregate independently