Chapter 24 Flashcards
Define quantitative genetics
Genetic analysis of complex characteristics
- Differentiate between discontinuous and continuous traits (Fig 24.1, 24.2)
- They may be encoded by genes at many loci (polygenic)
- They may be influenced by the environment
- They may be multifactorial - influenced by multiple genes and environmental factors
- Define meristic characteristic and explain why they are considered to be quantitative traits
Whole number characteristics, number of distinct phenotypes
- Define threshold characteristic and explain why they are considered to be quantitative traits even though
there are only 2 phenotypes (you have it or you do not have it)
Where there has to be a certain amount of stuff contributing for it to be present- quantitative because of multiple risk factors present
- Understand the inheritance of polygenic traits when the genes are additive (Fig 24.4—you do not have to
know the details of the Nilsson-Ehle cross, just understand how the problem in the figure is worked)
Sense squared= sum of (difference in each point from mean)^2 all over n-1
- Define heritability
Proportion of total phenotypic variation that is due to genetic differences
- Define phenotypic variance
Measure of the degree of phenotypic difference among a group of individuals; composed of genetic, environmental, and genetic–environmental interaction variances.
- Differentiate between broad-sense and narrow-sense heritability
- broad-sense heritability
o phenotypic variance due to genetic differences
o H2 =VG / VP - narrow-sense heritability
o phenotypic variance due to additive genetic variance
o h2 = VA / VP
- Understand the limitations to heritability
- an individual does not have heritability
- there is no universal heritability for a characteristic
- even when heritability is high, environmental factors may influence a characteristic
- Differentiate between natural selection and artificial selection
Natural- Organisms with beneficial traits pass on their genes
Artificial- Humans breed organisms for desirable traits
- Define response to selection (R)
How much a characteristic subjected to selection changes in one generation; equals the selection differential times the narrow-sense heritability.
- Define selection differential (S)
Difference between the mean phenotype of the selected parents and the mean phenotype of the original population
- Know how to calculate response to selection
narrow-sense heritability (^2) * Selection differential
genetic variance
Component of phenotypic variance that is due to genetic differences among individual members of a population.
additive genetic variance
Component of genetic variance that comprises the additive effects of genes on the phenotype.
dominance genetic variance
Component of genetic variance that can be attributed to dominance (interaction between genes at the same locus).
gene
interaction variance
Component of genetic variance that can be attributed to gene interaction (interaction between genes at different loci).
environmental variance
Component of phenotypic variance that is due to environmental differences among individual members of a population.
genetic-environmental variance
Component of phenotypic variance that results from an interaction between genotype and environment that causes genotypes to be expressed differently in different environments.
- Phenotypic variance (Vp)
(Genetic variance+ Environmental variance)
o Genetic variance (VG)
▪ Additive (VA)+ Dominance (VD)+ Gene Interaction (VI)
o Environmental variance (VE)
VE= Phenotypic variance- genetic variance
o Genetic-environment interaction variance (Definition and formula)
▪ the effect of the gene depends on the environment- VP= Vg+ Ve
