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.
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 12c
Textbook Question
In Drosophila, gray body color is dominant to ebony body color, while long wings are dominant to vestigial wings. Assuming that the P₁ individuals are homozygous, work the following crosses through the F₂ generation, and determine the genotypic and phenotypic ratios for each generation. gray, long x gray, and vestigial.

1
Step 1: Define the alleles for the traits. Let 'G' represent the dominant allele for gray body color, 'g' represent the recessive allele for ebony body color, 'L' represent the dominant allele for long wings, and 'l' represent the recessive allele for vestigial wings.
Step 2: Write the genotypes of the P₁ generation. Since the P₁ individuals are homozygous, the gray, long parent will have the genotype GGLL, and the gray, vestigial parent will have the genotype GGll.
Step 3: Determine the gametes produced by the P₁ individuals. The gray, long parent (GGLL) can only produce gametes with the alleles 'GL', while the gray, vestigial parent (GGll) can only produce gametes with the alleles 'Gl'.
Step 4: Perform the F₁ cross. Combine the gametes from the P₁ generation to determine the F₁ offspring. All F₁ individuals will have the genotype GGLl, which is heterozygous for the wing trait but homozygous for the body color trait. The phenotype of all F₁ individuals will be gray body color with long wings.
Step 5: Perform the F₂ cross. Cross the F₁ individuals (GGLl x GGLl) to determine the genotypic and phenotypic ratios in the F₂ generation. Use a Punnett square to combine the alleles for both traits, considering all possible combinations of gametes (GL, Gl, gL, gl). Then, count the genotypes and phenotypes to determine the ratios.

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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Dominance in Genetics
Dominance refers to the relationship between alleles, where one allele masks the expression of another in a heterozygous individual. In this case, gray body color and long wings are dominant traits, meaning that if an individual has at least one allele for these traits, they will express the dominant phenotype. Understanding dominance is crucial for predicting the outcomes of genetic crosses.
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Variations on Dominance
Punnett Square
A Punnett square is a diagram used to predict the genotypic and phenotypic ratios of offspring from a genetic cross. By organizing the alleles of the parents, it allows for a visual representation of all possible combinations in the F1 and F2 generations. This tool is essential for analyzing inheritance patterns and determining the likelihood of specific traits appearing in offspring.
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Chi Square Analysis
Homozygosity and Heterozygosity
Homozygosity occurs when an individual has two identical alleles for a particular gene, while heterozygosity refers to having two different alleles. In the given question, the P₁ individuals are homozygous, which simplifies the initial cross since all gametes will carry the same allele. Understanding these terms is vital for predicting the genetic makeup of the offspring in subsequent generations.
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Hardy Weinberg
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