Traits

Qualitative trait  

Phenotypic variation is NOT continuous and CAN BE separated into discrete classes  

Distinct and discontinues is the concept of qualitative trait  

• Rolling their tongue  

• How many can kinda, it is a YES or NO question = distinct and discontinues  

• Either have it or don’t 

Quantitative trait  

Phenotypic variation IS continuous and CANNOT be separated into discrete classes  

• Height  

• On going list from shortest to tallest  

• Know people that are 5'0, 5'1 ½  

  • Everything is possible  

• Chart it with large enough population shows a normal distribution  

  • with a mean  

Qualitative vs Quantitative  

Gene for gene theory  

For every gene for susceptibility there is an equal and opposite gene for resistance 

if it was a qualitative trait there would be dead and live plants after pathogen  

• After time population develops immunity overcoming disease gaining resistance  

  • Shifting to more living plants  

Biosynthetic pathway control  

Accumulation controlled by flow  

• Each step regulated by genes  

• Steps can be up/down regulated

Variation  

Two types of variation  

• Environmental variation  

  • Due to the environment in which the plant is grown in  

• Heritable variation  

  • Differences in plants regulated by genes 

  • Genes will follow heredity law  

Environmental variation  

Variation in phenotype in response to different intensities of environment al stress  

Testing for environmental variation  

• Homogenous population in same environment 

• Uniform population – same gene  

Variation is not transmitted to the progeny 

Heritable variation  

Variation in phenotype which is transmitted to the progeny  

Testing for heritable variation  

• Heterogeneous population in the same environment

Heritability (h^2)  

The proportion of the observed variation in a progeny which is inherited  

Calculated relationship between genetics, environment and G x E  

• We can calculate the genetics and environment but we're not multiplying both  

Simplest method :  

• Variance  

Variance (V)  

Dispersion of observations in a population – how much does a trait vary  

• Squared deviation from a mean  

• Std. Dev. (SD) = square root variance  

Variance components:  

VP = Phenotypic Variance, height  
VG = Genotypic Variance 
VE = Environmental Variance 
VGxE = Interaction Variance - genotype in environment interact  
VA = Additive Variance – this allele adds this much 
VD = Dominant Variance -  
VI = Epistatic Variance – interaction between genes  

Phenotypic variance  

Dispersion of the observed phenotypic variation  

• Divided into three components  

Vp= Vg+Ve+Vgxe  

Genotypic variance  

Variation accounted for by the genes  

• Also divided into 3 components  

Vg= Va+Vd+Vi 

Heritability  

Broad sense heritability  

If breeding in clonal/ cuttings   

Value of genetic gain  

Predict how much improvement in the next generation – given some information  

If I select those plants and plant how much would population change