lec. 25 quantitative genetics

qualitaitve/discontinuous traits

• single gene

• environment does NOT affect phenotype

• distinct, non-overlapping classes

Quantitative/continuour traits

• two or more genes involved

• environment affects phenotype

• continuous range

There are variantions in phenotypes due to

genotype and environment

Vp

variation in P

variation in

How to make variation in phenotype only due to environment?

Reduce the variation in genotype to 0 by using homozygous animal model

How to make variation in phenotype only due to genotype?

reduce Ve to 0 by putting all animals in smae environment

Polygenic Model of Inheritance

1. mutliple genes contribute to color

2. each gene adds a unit of something

3. more loci → more possible genotypes

Vge

genetic-environmental interaction variation

Va

additive; resemblance b/w parents and offspring

Vd

dominacne; effect of 1 alled

Vi

genic interaction; epistasis

Heritability

amount of variation in a phenotype due to genetic differences among individuals

conditions for heritability

• specific for a particular pop.

• not appicable to indidiuvals

• can change if enviornment changes

broad-sense heritability

0-1; 0 = no variation is due to genotype variation

1 = all variation due to genotypic variation

narrow-sense heritability

used to predict how phenotypuc distribution will change if environemtn is modified

a high h² indicated

• much of variation is due to geentic variation

• trait should repsond to selection

Hn² (realized heritability) can be determined by..

selective breeding

R

response to selection; how much characterisistics chnage after 1 generation of selective breeding

Xo

mean of offspring

Xp

mean of parents

S

selective differenetial; magnitude of selection