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Lecture 5:Chapter 3.3 Quantitative genetics
Many traits take quantitative instead of qualitative values, and are determined by many genes
Genetics and inheritance of quantitative traits is described in statistical terms.
Quantitative traits:
- Traits affected by many genes and the environment
- Also known as “complex traits”
- Typical examples:
o Fitness
o Body weight
o Growth rate
o Egg number
o Seed yield
o Asthma
o Schizophrenia
o Resistance to infectious diseases
o Intelligence
o Human height
Quantitative genetics:
- The genetics of quantitative traits
o Is the foundation of animal breeding
o Was developed by agriculturist
Together with statistics
o Very much an applied science
Livestock and plant breeding
Powerful tools : “it works”
You can change populations
o No knowledge of the genes required
Statistical genetics
In the past: Little insight in genetic background/ genes
Recent: GWAS more knowledge of genes
Quantitative trait vs qualitative traits:
- Qualitative traits:
o Individuals cannot be ordered from low to high values of the traits
, E.g. coat colour types
- Quantitative traits have a value
o Trait values can be expressed on a scale from low to high
o For example
Body weigh in rabbits
Fitness
Lifetime
Litter size
Teat number in pigs.
Continuous quantitative trait:
- Continuous: all trait values are possible
- We have a continuous distribution (often normal)
-
Categorical quantitative traits:
- Categorical traits (meristic traits)
o Trait values fall into a limited number of categories
Countable traits
Number of offspring, number of ears, number of seeds
But not body weight.
o Histograms of frequency
Bristle number in drosophila.
,
The basic of quantitative genetic model:
- Phenotype = genotype + environment.
-
Genotypic value: the average value of the genotype.
The environmental effect is a deviation from the average.
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