Table of contents
- 1. Introduction to Biology2h 42m
- 2. Chemistry3h 37m
- 3. Water1h 26m
- 4. Biomolecules2h 23m
- 5. Cell Components2h 26m
- 6. The Membrane2h 31m
- 7. Energy and Metabolism2h 0m
- 8. Respiration2h 40m
- 9. Photosynthesis2h 49m
- 10. Cell Signaling59m
- 11. Cell Division2h 47m
- 12. Meiosis2h 0m
- 13. Mendelian Genetics4h 44m
- Introduction to Mendel's Experiments7m
- Genotype vs. Phenotype17m
- Punnett Squares13m
- Mendel's Experiments26m
- Mendel's Laws18m
- Monohybrid Crosses19m
- Test Crosses14m
- Dihybrid Crosses20m
- Punnett Square Probability26m
- Incomplete Dominance vs. Codominance20m
- Epistasis7m
- Non-Mendelian Genetics12m
- Pedigrees6m
- Autosomal Inheritance21m
- Sex-Linked Inheritance43m
- X-Inactivation9m
- 14. DNA Synthesis2h 27m
- 15. Gene Expression3h 6m
- 16. Regulation of Expression3h 31m
- Introduction to Regulation of Gene Expression13m
- Prokaryotic Gene Regulation via Operons27m
- The Lac Operon21m
- Glucose's Impact on Lac Operon25m
- The Trp Operon20m
- Review of the Lac Operon & Trp Operon11m
- Introduction to Eukaryotic Gene Regulation9m
- Eukaryotic Chromatin Modifications16m
- Eukaryotic Transcriptional Control22m
- Eukaryotic Post-Transcriptional Regulation28m
- Eukaryotic Post-Translational Regulation13m
- 17. Viruses37m
- 18. Biotechnology2h 58m
- 19. Genomics17m
- 20. Development1h 5m
- 21. Evolution3h 1m
- 22. Evolution of Populations3h 52m
- 23. Speciation1h 37m
- 24. History of Life on Earth2h 6m
- 25. Phylogeny2h 31m
- 26. Prokaryotes4h 59m
- 27. Protists1h 12m
- 28. Plants1h 22m
- 29. Fungi36m
- 30. Overview of Animals34m
- 31. Invertebrates1h 2m
- 32. Vertebrates50m
- 33. Plant Anatomy1h 3m
- 34. Vascular Plant Transport1h 2m
- 35. Soil37m
- 36. Plant Reproduction47m
- 37. Plant Sensation and Response1h 9m
- 38. Animal Form and Function1h 19m
- 39. Digestive System1h 10m
- 40. Circulatory System1h 49m
- 41. Immune System1h 12m
- 42. Osmoregulation and Excretion50m
- 43. Endocrine System1h 4m
- 44. Animal Reproduction1h 2m
- 45. Nervous System1h 55m
- 46. Sensory Systems46m
- 47. Muscle Systems23m
- 48. Ecology3h 11m
- Introduction to Ecology20m
- Biogeography14m
- Earth's Climate Patterns50m
- Introduction to Terrestrial Biomes10m
- Terrestrial Biomes: Near Equator13m
- Terrestrial Biomes: Temperate Regions10m
- Terrestrial Biomes: Northern Regions15m
- Introduction to Aquatic Biomes27m
- Freshwater Aquatic Biomes14m
- Marine Aquatic Biomes13m
- 49. Animal Behavior28m
- 50. Population Ecology3h 41m
- Introduction to Population Ecology28m
- Population Sampling Methods23m
- Life History12m
- Population Demography17m
- Factors Limiting Population Growth14m
- Introduction to Population Growth Models22m
- Linear Population Growth6m
- Exponential Population Growth29m
- Logistic Population Growth32m
- r/K Selection10m
- The Human Population22m
- 51. Community Ecology2h 46m
- Introduction to Community Ecology2m
- Introduction to Community Interactions9m
- Community Interactions: Competition (-/-)38m
- Community Interactions: Exploitation (+/-)23m
- Community Interactions: Mutualism (+/+) & Commensalism (+/0)9m
- Community Structure35m
- Community Dynamics26m
- Geographic Impact on Communities21m
- 52. Ecosystems2h 36m
- 53. Conservation Biology24m
13. Mendelian Genetics
Dihybrid Crosses
Problem 1
Textbook Question
Two pea plants heterozygous for the characters of pod color and pod shape are crossed. Draw a Punnett square to determine the phenotypic ratios of the offspring.

1
Step 1: Identify the genotypes of the parent plants. Since both plants are heterozygous for pod color and pod shape, their genotypes are 'GgSs', where 'G' represents the dominant allele for green pod color, 'g' represents the recessive allele for yellow pod color, 'S' represents the dominant allele for smooth pod shape, and 's' represents the recessive allele for constricted pod shape.
Step 2: Determine the possible gametes each parent can produce. Use the FOIL (First, Outer, Inner, Last) method to combine the alleles for each trait. For a 'GgSs' parent, the possible gametes are 'GS', 'Gs', 'gS', and 'gs'.
Step 3: Set up a 4x4 Punnett square. Label the rows with the gametes from one parent ('GS', 'Gs', 'gS', 'gs') and the columns with the gametes from the other parent ('GS', 'Gs', 'gS', 'gs').
Step 4: Fill in the Punnett square by combining the alleles from the rows and columns. For example, the combination of 'GS' (row) and 'Gs' (column) would result in the genotype 'GGSs'. Repeat this process for all 16 squares in the Punnett square.
Step 5: Analyze the genotypes in the Punnett square to determine the phenotypic ratios. Group the offspring based on their phenotypes (e.g., green smooth, green constricted, yellow smooth, yellow constricted) by considering the dominance of the alleles ('G' is dominant over 'g', and 'S' is dominant over 's'). Count the number of each phenotype 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.
Punnett Square
A Punnett square is a diagram used to predict the genotypes and phenotypes 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 case, it will help determine the ratios of different phenotypes resulting from the cross of two heterozygous pea plants.
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Punnett Squares
Heterozygous
Heterozygous refers to an organism that has two different alleles for a particular gene, one inherited from each parent. In the context of the pea plants, being heterozygous for pod color and pod shape means that each plant carries one dominant and one recessive allele for these traits. This genetic variation is crucial for understanding the potential outcomes in the offspring.
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Dihybrid Crosses
Phenotypic Ratio
The phenotypic ratio is the relative frequency of different phenotypes in the offspring resulting from a genetic cross. It is calculated by analyzing the outcomes from the Punnett square, which shows how traits are expressed based on the combinations of alleles. Understanding phenotypic ratios helps in predicting the likelihood of certain traits appearing in the next generation.
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Genotypic vs. Phenotypic Ratio
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