Genetics Final - Quantitative Genetics

Quantitative Trait

Wide range of phenotypes, multiple genes (although can be one + environment), Vp=Vg+Ve+Vge. Dosage vs threshold and meristic. As loci increase, phenotypic classes increase.

Qualitative Traits

Few distinct phenotypes, few contributing genes.

RA Fischer

Quantitative traits caused by multiple genes -→ continuous phenotypes.

Wheat Kernel Color

3 Distinct genes, each contribute same amount, red color mix

Dosage effect in one gene

Phenotype ratio = genotype ratio.

Quantitative Trait Loci

Locus that contributes to a quantitative trait.

Quantitative trait gene vs environment

Heritability → proportion due to genetic difference. Environmental, gene by environment.

Determine Proportion of Variance due to gene vs environment

Environment: control for genotype, place in different environments

Heritability: control for environment, genetically different organisms.

Phenotypic variance: grow diverse genotype in diverse environment

Human heritability of trait

If heritability high → MZ=DZ=UR, if low → MZ>DZ>UR

Heritability limitations

• Doesnt show degree of genetic determination

• Individuals dont have heritability

• No universal heritability

• Environment can always have an influence

Mapping Types

QTL - Cross between individuals that differ in phenotype of interest.

Association mapping - Take advantage of random breeding in population.

Use haplotypes/markers.

Large vs Small effect QTL

Trait can be caused by few large effect, lots of small effect, or mix.

Tomato QTL Mapping

Start with isogenic small and large, cross. All of F1 are medium. Backcross F1 to large → range of phenotypes. Difference in mean weight of allele for aa marker shows linkage to QTL. 28 total.

Once we know marker position from QTL mapping →

Is there expression of something nearby, are there known orthologs, are there biochemical predictions. Difference could be due to CREs (spatiotemporal expression amounts), or splice sites.

Nearly Isogenic Lines

Produced by backcrossing BC1 many times → all progeny nearly homozygous to one species except small region. Compare boundaries of NIL to find region. Test by transfecting causal gene into opposite phenotype. Also corn example.