Which of the following represent trait variation caused from genetic variation?
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
20. Quantitative Genetics
Analyzing Trait Variance
Problem 4d
Textbook Question
A dark-red strain and a white strain of wheat are crossed and produce an intermediate, medium-red F₁. When the F₁ plants are interbred, an F₂ generation is produced in a ratio of 1 dark-red: 4 medium-dark-red: 6 medium-red: 4 light-red: 1 white. Further crosses reveal that the dark-red and white F₂ plants are true breeding
Predict the outcome of the F1 and F2 generations in a cross between a true-breeding medium-red plant and a white plant.

1
Step 1: Analyze the inheritance pattern. The F₁ generation shows intermediate phenotypes, suggesting incomplete dominance or polygenic inheritance. The F₂ generation ratio (1:4:6:4:1) indicates two genes with additive effects controlling the trait.
Step 2: Identify the genotypes of the true-breeding medium-red plant and the white plant. A true-breeding medium-red plant likely has a heterozygous genotype for both genes (AaBb), while the white plant is homozygous recessive for both genes (aabb).
Step 3: Set up a Punnett square for the cross between AaBb (medium-red) and aabb (white). The gametes from AaBb will be AB, Ab, aB, and ab, while the gametes from aabb will all be ab.
Step 4: Fill in the Punnett square to determine the genotypes of the offspring. Combine each gamete from AaBb with ab from aabb to produce offspring genotypes such as AaBb, Aabb, aaBb, and aabb.
Step 5: Predict the phenotypes of the offspring based on the genotypes. Use the additive effects of the alleles to determine the color intensity for each genotype, and calculate the phenotypic ratio for the generation.

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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Incomplete Dominance
Incomplete dominance occurs when the phenotype of the heterozygote is intermediate between the phenotypes of the two homozygotes. In this case, crossing a dark-red strain with a white strain produces an F₁ generation that is medium-red, illustrating that neither allele is completely dominant over the other.
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Variations on Dominance
Genotypic Ratios
Genotypic ratios represent the relative frequencies of different genotypes produced in a genetic cross. The F₂ generation's ratio of 1 dark-red: 4 medium-dark-red: 6 medium-red: 4 light-red: 1 white indicates a complex inheritance pattern, likely involving multiple alleles and interactions, which can be analyzed using a Punnett square.
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Gamete Genotypes
True Breeding
True breeding refers to organisms that, when mated, produce offspring with the same phenotype as themselves. In this scenario, the dark-red and white F₂ plants are true breeding, meaning they consistently pass on their specific traits to their offspring, which is crucial for predicting the outcomes of future crosses.
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Chi Square Analysis
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