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
QTL Mapping
1:20 minutes
Problem 23
Textbook Question
Textbook QuestionType A1B brachydactyly (short middle phalanges) is a genetically determined trait that maps to the short arm of chromosome 5 in humans. If you classify individuals as either having or not having brachydactyly, the trait appears to follow a single-locus, incompletely dominant pattern of inheritance. However, if one examines the fingers and toes of affected individuals, one sees a range of expression from extremely short to only slightly short. What might cause such variation in the expression of brachydactyly?
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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 is a genetic scenario where neither allele is completely dominant over the other, resulting in a phenotype that is a blend of both traits. In the case of brachydactyly, this means that individuals with one normal allele and one brachydactyly allele may exhibit a phenotype that is intermediate between the two, leading to variability in the expression of the trait.
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Variations on Dominance
Phenotypic Variation
Phenotypic variation refers to the observable differences in traits among individuals, which can arise from genetic differences, environmental influences, or a combination of both. In the context of brachydactyly, the range of finger and toe lengths among affected individuals illustrates how genetic factors can interact with other variables to produce diverse phenotypes.
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Genomic Variation
Polygenic Inheritance
Polygenic inheritance involves multiple genes contributing to a single trait, leading to a continuous range of phenotypes. Although brachydactyly is described as a single-locus trait, the observed variation in expression may suggest the influence of additional genes or environmental factors, complicating the inheritance pattern and resulting in a spectrum of phenotypic outcomes.
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