Let’s explore the inheritance of two characters in MendAliens, a mythical alien species. We will look at eye color and skin color. Let’s start by crossing a black-eyed, green-skinned MendAlien with an orange-eyed, white-skinned MendAlien. The F1 offspring all have black eyes and green skin, so we know that the allele for black eyes is dominant to the allele for orange eyes, and the allele for green skin is dominant to the allele for white skin. Now let’s make the F1 by F1 cross. If we look at just eye color in the F2 generation, there are 293 individuals with black eyes plus another 96 individuals with black eyes, for a total of 389 individuals with black eyes. There are 104 individuals with orange eyes plus another 34 individuals with orange eyes, for a total of 138 individuals with orange eyes. This is a ratio of approximately 3 black-eyed individuals to 1 orange-eyed individual, the expected ratio in the F2 generation when F1 hybrids are crossed. Similarly, there are approximately 3 green-skinned individuals for every 1 white-skinned individual. Now let's look at both eye color and skin color in the F2 generation to determine if these characters are inherited as a package or inherited independently. The F2 phenotypic ratio is approximately 9 black eyes, green skin to 3 black eyes, white skin to 3 orange eyes, green skin to 1 orange eyes, white skin. The 9 to 3 to 3 to 1 ratio indicates that this is a dihybrid cross--a cross between F1 dihybrids, individuals who are heterozygous for the two characters being followed in the cross. The 9 to 3 to 3 to 1 ratio in this dihybrid cross shows that the genes for eye color and skin color assort independently. Since this is a dihybrid cross, the parents must have been true-breeding, so we can now assign alleles to the individuals and their gametes. Let’s use capital B for the black-eyes allele and small b for the orange-eyes allele, and capital G for the green-skin allele and small g for the white-skin allele. The parent with black eyes and green skin is homozygous dominant for both characters (capital B, capital B, capital G, capital G), and the parent with orange eyes and white skin is homozygous recessive for both characters (small b, small b, small g, small g). The parental gametes are therefore capital B capital G and small b small g. The F1 MendAliens are heterozygous for both characters (capital B, small b, capital G, small g). They have black eyes and green skin because the black-eyes allele (capital B) is dominant to the orange-eyes allele (small b), and the green-skin allele (capital G) is dominant to the white-skin allele (small g). Here are the results of the F1 by F1 cross. The Punnett square for the F2 generation predicts a ratio of 9 MendAliens with black eyes and green skin to 3 MendAliens with black eyes and white skin to 3 MendAliens with orange eyes and green skin to 1 MendAlien with orange eyes and white skin. The observed F2 phenotypic ratio closely matches the expected ratio of 9 to 3 to 3 to 1. We can conclude that the genes for eye color and skin color assort independently. If an unknown MendAlien has the dominant traits of black eyes and green skin, how can we figure out its genotype? We can perform a testcross with an individual that exhibits both recessive traits--orange eyes and white skin. This diagram illustrates the results of one such test cross. In this case, there are four different types of offspring in a 1 to 1 to 1 to 1 ratio, so the MendAlien with black eyes and green skin must have all four possible alleles --the black eyes allele (capital B), the orange eyes allele (small b), the green skin allele (capital G), and the white skin allele (small g). In other words, our mystery MendAlien is heterozygous for both eye color and skin color.
Table of contents
- 1. Introduction to Biology2h 40m
- 2. Chemistry3h 40m
- 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 41m
- Introduction to Mendel's Experiments7m
- Genotype vs. Phenotype17m
- Punnett Squares13m
- Mendel's Experiments26m
- Mendel's Laws18m
- Monohybrid Crosses16m
- 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 20m
- 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 Transport2m
- 35. Soil37m
- 36. Plant Reproduction47m
- 37. Plant Sensation and Response1h 9m
- 38. Animal Form and Function1h 19m
- 39. Digestive System10m
- 40. Circulatory System1h 57m
- 41. Immune System1h 12m
- 42. Osmoregulation and Excretion50m
- 43. Endocrine System4m
- 44. Animal Reproduction2m
- 45. Nervous System55m
- 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
Video duration:
4mPlay a video:
Related Videos
Related Practice