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BIOC16H3 (11)
Lecture 7

BIOC16 Lecture 7.pdf

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Biological Sciences
Mark Fitzpatrick

BIOC16 - Lecture 7! ! Quantitative genetics II! Remember! ! ! We want to understand phenotypic variation in outbreeding species! To do this we estimate variances and heritability's using phenotypic measurements of individuals with known genetic relationships! We do this by relating parents to offspring ( for heritability or sexual trait) or sibling to sibling (if you care about the particular moment) and sometimes even half siblings (eg looking at maternal effects by looking at siblings with same mother but different fathers). Offspring-Parent Regression-! Need an adequate number of monogamously mated pairs for the parental generation! ! ! ! ! Always go for more families than more siblings ! -measure the trait in one or both parents! - rear offspring to some developmental stage at which parents were measured! - measure offspring ! ! ! ! ! If slope = 1 then a parental increase of 1leads to an offspring increase of 1! If slope = 0.5 then a parental increase of 1 leads to an offspring increase of 0.5! Therefore only half of the phenotypic variance is additive genetic variance!!!! ! What about the other half?! - non additive! - environment! - therefore it doesn't contribute to resemblance of parents and offspring! ! Does this imply that the total phenotypic variance of the offspring is half that of the parents?! NO! Because of the environment and non additive genetic variance, it is expressed in the variance among full siblings within each family.! -you remove this variance by using a single mean of the offspring rather than individual offspring values This point represents the parents and the offspring Maternal and Paternal Effects! -from previous example, we assumes all resemblance between parents and offspring was due to genetics. ! - what about parental care, provisioning of the young, teaching, etc.! ! Eg: the amount and quality of parental care depends on the value of trait of interest in parents and the amount or quality of care partly determines the value of that same trait in the offspring.! - this gives rise to non genetic resemblance between parents and offspring! - the most common of these are maternal effects because usually females put more effort in caring for young. - maternal effects - gestation, lactation, direct care of young! - paternal effects - eg care of egg etc! ! So how can we obtain estimates of variance and heritability that aren't contaminated by these effects? Cross-Fostering! -common in birds! -phenotype of young are regressed on genetic parents ... Leads to a good estimate of heritability since it controls for parental effects.! - regression of offspring on foster parents to get an estimate of parental effects. Chapter 5! Phenotypic Plasticity! -traits are expressed differently in different environments ( real environments)! - if different genotypes differ in the level or direction of plasticity they express then we will see GxE (gene by environment interaction) ! -we visualize these by reaction norms.! ! Each line represents a different father! -We see an effect of the father (sire) but no effect of the environment and no effect of GxE in example 1.! -In example 2 we see an effect of sire and of the environment but no GxE interaction.! -In example 3, we see no effect of sire, no predictable environment effect but there is a gene The main representation of GxE interactions is the crossing over of the lines.! In example 4, there is sire and GxE but no environment. The environment here is a "macro environment"! -forest vs field! -lake with low pH vs lake with high pH! -steepness of slope indicates the amount of plasticity in the family! In example 1, we see no plasticity, the same phenotype in each environment, families themselves differ, VA is approximately the same in each environment! In example 2 we see high plasticit
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