2 An Overview of Quantitative Genetics
2.2 Quantitative Genetics and Phenotypic Evolution
The “main principles” has been outlined independently by Ronald Fisher (1918) and Sewall Wright (1921).
Theoretical basis for most plant and animal breeding programs for well over a half century.
Complex human genetic disorders
Evolutionary biology (1980-)
Molecular biology
Francis Galton: empirical motivation
Karl Pearson: formal development of the theory of regression and correlation
Ronald Fisher: concept of variance-component partitioning (analsis of varaince, ANOVA), the development of methods for experimental design and hypothesis testing
Sewall Wright: path analysis.
2.4 The Major Goals of Quantitative Genetics
2.4.1 The nature of quantitative-trait variation
- Partitioning phenotypic variance into its various compoents (Chapters 17-27)
- the phenotypic resemblance between relatives provides information on the degreee of genetic differentiation among individuals (Chapter 7)
- Genotype * environment interaction (Chapter 22)
- There are several components of both environmental and genetic variation (Chapters 4, 5, and 6)
- The additive component of the genetic variance (the variance of breeding value) is of particluar interest
Utimately, the pool of genetic variation in a population must be due to quasi-balance between the forces of selection and random genetic drift, both of which tend to eliminate variation, and the replenishing force of mutation.
- mutational rate of production of new variation (Chapter 12)
- the number of loci underlying a character is likely to be large or small (Chapters 9 and 13)
- molecular-marker-based approaches, QTLs (Chapters 14-16)
- nonadditive effect (Chapter 5)
- Chapter 11
2.4.2 The consequences of inbreeding and outcrossing
Inbreeding effects are almost always deleterious, generally increasing linearly with the degree os relatedness between parents (Chapter 10)
Crosses between isolated lines or populations often exhibit “hybrid vigor” in the F1 generation, only to be followed by substantial fitness decline in the next (F2) generation. (Chapter 9)