Two organisms with the genotypes Aa bb Cc Dd Ee and Aa Bb Cc dd Ee were crossed. Use the branch method to determine the proportion of the following genotypes in the offspring. III. AA BB CC Dd ee
Table of contents
- 1. Introduction to Genetics51m
- 2. Mendel's Laws of Inheritance3h 37m
- 3. Extensions to Mendelian Inheritance2h 41m
- 4. Genetic Mapping and Linkage2h 28m
- 5. Genetics of Bacteria and Viruses1h 21m
- 6. Chromosomal Variation1h 48m
- 7. DNA and Chromosome Structure56m
- 8. DNA Replication1h 10m
- 9. Mitosis and Meiosis1h 34m
- 10. Transcription1h 0m
- 11. Translation58m
- 12. Gene Regulation in Prokaryotes1h 19m
- 13. Gene Regulation in Eukaryotes44m
- 14. Genetic Control of Development44m
- 15. Genomes and Genomics1h 50m
- 16. Transposable Elements47m
- 17. Mutation, Repair, and Recombination1h 6m
- 18. Molecular Genetic Tools19m
- 19. Cancer Genetics29m
- 20. Quantitative Genetics1h 26m
- 21. Population Genetics50m
- 22. Evolutionary Genetics29m
2. Mendel's Laws of Inheritance
Dihybrid Cross
Problem 7
Textbook Question
Mendel crossed peas having round seeds and yellow cotyledons (seed leaves) with peas having wrinkled seeds and green cotyledons. All the F₁ plants had round seeds with yellow cotyledons. Diagram this cross through the F₂ generation, using both the Punnett square and forked-line, or branch diagram, methods.

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Step 1: Identify the parental genotypes and phenotypes. The round seed (R) and yellow cotyledon (Y) traits are dominant, while the wrinkled seed (r) and green cotyledon (y) traits are recessive. The parental cross involves homozygous dominant (RRYY) and homozygous recessive (rryy) individuals.
Step 2: Determine the F₁ generation genotypes and phenotypes. Since the parental cross is between RRYY and rryy, all F₁ offspring will be heterozygous (RrYy) and exhibit the dominant phenotypes: round seeds and yellow cotyledons.
Step 3: Set up the F₂ generation cross. Cross two F₁ individuals (RrYy × RrYy). Use the Punnett square method to determine the genotypic and phenotypic ratios. Create a 4x4 Punnett square, with each parent contributing gametes (RY, Ry, rY, ry). Fill in the square by combining the alleles from each parent.
Step 4: Use the forked-line (branch diagram) method to calculate the phenotypic ratios. For each trait, calculate the probabilities of dominant and recessive phenotypes independently. Multiply the probabilities for seed shape (round vs. wrinkled) and cotyledon color (yellow vs. green) to determine the overall phenotypic ratios.
Step 5: Summarize the results. The F₂ generation will exhibit a phenotypic ratio of 9:3:3:1 (9 round yellow, 3 round green, 3 wrinkled yellow, 1 wrinkled green). This ratio reflects the independent assortment of the two traits, as described by Mendel's second law.

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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Mendelian Genetics
Mendelian genetics is the study of how traits are inherited through generations, based on the principles established by Gregor Mendel. It involves understanding dominant and recessive alleles, where dominant traits mask the expression of recessive ones. In this case, round seeds and yellow cotyledons are dominant traits, while wrinkled seeds and green cotyledons are recessive.
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Descriptive Genetics
Punnett Square
A Punnett square is a diagram used to predict the genotypes of offspring from a genetic cross. It organizes the possible combinations of alleles from each parent, allowing for a visual representation of inheritance patterns. In this scenario, the Punnett square will help illustrate the expected ratios of round versus wrinkled seeds and yellow versus green cotyledons in the F₂ generation.
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Chi Square Analysis
Forked-Line (Branch) Diagram
The forked-line or branch diagram is another method for visualizing genetic crosses, particularly useful for tracking multiple traits. It systematically branches out to show all possible combinations of alleles from each parent, similar to a tree structure. This method can effectively demonstrate the inheritance of both seed shape and cotyledon color in the F₂ generation.
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Branch Diagram
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