L3 Quantitative genetics and linkage mapping

Question 1

QTL (quantitative trait loci) mapping

Answer 1

Combine quantitative genetic analysis with genome-wide mapping. Allows you to identify a number of gene regions (QTL), their effect size, and their type of action. More sophisticated analysis allows identification of epistasis and pleitropy.

Question 2

Quantitative traits

Answer 2

Different from discrete phenotypes. Continuous variables (weight, height) a smooth distribution. Behavior, morphology, physiological processes, disease susceptibility, etc.

Question 3

Causes of continuous distribution

Answer 3

1. Several genes make up a trait: 2 genes, with each 2 alleles either 2 high (HH), 2 low (LL) or one of each (LH)
2. large degree of environmental variation affects the trait: only one gene affects the trait, but the environmental variation smooths the distribution.

Question 4

Identifying genetic architecture of quantitative traits

Answer 4

-Number of genes that are involved, their relative effect strength, their mode of action
- Two possible routes:
1. Top-down (forward) approach
2. Bottom-up (reverse) approach

Question 5

Top-down approach

Answer 5

Statistical genetics: simply by measuring the phenotype and with knowledge of the pedigree, one can infer several facts.

Question 6

Heritability

Question 7

Breeding designs

Answer 7

-Parent/offspring correlation: Half-sib design, full-sib design (pedigree of half-sibs). Within versus between family variations is analyzed.

Question 8

Statistical genetics

Answer 8

Study of genes or genetic markers, and their transmission from parent to offspring. Use of recombination to estimate genetic map and QTL location.

Question 9

Statistical genomics

Answer 9

Unit of study in this instance is the base pairs that make up the gene and how these differ between individuals.

Question 10

Genetic mapping

Answer 10

-Linkage overview- crossing over
- Genetic maps- historical overview
- Marker segregation
- Ordering markers on a map
- Map distances

Question 11

Synthetic linkage

Answer 11

Genes that are physically close to one another on the chromosome (therefore these genes are linked). Genes that are further apart on a chromosome are unlinked. Linkage between two genes is defined as less than 50% recombination between them.

Question 12

Crossing over

Answer 12

Recombination between genes ascertained due to crossing-over events. These occur during meiosis. Chromatids pair up and can then recombine.

Question 13

Marker types

Answer 13

-SNPs- single nucleotide polymorphisms
-SSRs- simple sequence repeats- microsatellites
-RFLPs- restriction fragment length polymorphisms.