L12 Quantitative Traits

Discrete

• discontinuous variation

• few, distinct categories

• not affected by envt

• show mendelian inheritance

• controlled by few genes

Quantitative

• continuous variation

• no distinct categories

• strong envtal influence

• show complex inheritance

• controlled by many genes

What is the difference, if any, between a gene, locus, and allele?

quantativave traits are traits

that vary continuously and are affected by many (sometimes thousands) of genes

for example:

• height

• skin color

• milk production

these are call polygenetic traits

usually follow a normal bell shape curve

phenotypic distribution is

dependent on genetic and environmental factors

genetic factors

the more loci involved in a trait, the smoother the curve will be

Environmental factors

the more environmental variance the expression of a trait the smoother the curve will be

why does having more loci underly a trait smooth out the distribution curve?

There are more combinations providing more combinations

phenotypic variance

variance in a trait within a population

Vp = Vg + Ve + Vge

p = phenotypic variance

g = genetic variance

e = environmental variance

ge = gene x environment interactions

Phenotypic variance is a function of what

a. genetic variance

b. fitness variance

c. environmental variance

d. selection variance

genetic and environmental

genetic variance

is the part of phenotypic variance that is caused by variation in genotype and heritability

Heritability measures

the strenght of inheritance; how much a genotype can predict a specific phenotype

Environmental variance

the part of phenotypic variance that is caused by variation in environment rather than genotype

causes individuals with the same genotype to have different phenotypes

Phenotype plasticity

the ability of one genotype to produce more than one phenotype when exposed to different environments

reaction norms

a plot showing how environment affects phenotypes

The same genotype can respond to envt differently =

plasticity

when plasticity is dependent on genotype and envt =

GxE interaction

Genotype envt (GxE) interactions

occurs when different genotypes respond to environmental variation in different ways

occur when phenotypic plasticity is different for different genotypes

Which graph(s) show ONLY plasticity

Only B bc they are changing with the envt and the slope is the same (they are both responding the same to the envt)

not C because there is a GxE interaction bc one is responding differently

Which graph(s) show both plasticity and GxE interactions

C and D

genotype-envt interactions

• two different populations of water fleas have different responses to UV levels

• those that have evolved with predators have little plasticity

• those that evolved without predators have higher plasticity

is plasticity adaptive?

It depends because being plastic in one environment may be beneficial while in another it isn't; so it depends on the envt

Variegation in plants occurs as a result of a genetic mutation which reduces chlorophyll production and alters the coloration of the leaves. When grown under insufficient light, variegated plants will tend to lose their variegation and revert to a normal

a reaction norm

phenotypic plasticity and GxE interaction

phenotypic plasticity ONLY

GxE interaction ONLY

phenotypic plasticity ONLY

Can you have GxE interactions without plasticity

no