Download The Human Genome, then begin Quantitative Genetics

BIO421
Advanced Genetics
Lecture 14
The Human Genome and begin Quantitative Genetics
I. Human Genome
A. History of the genome effort
B. Methods of sequencing the human genome
1. BAC to BAC: the hugo project.
2. All shotgun: the Celera project
C. What we have learned from the human chromosome
1. Nucleotide makeup
2. Transposable elements
3. Nucleotide substitutions
4. The history of our genes
5. Disease genes
6. History of our chromosomes
I. Quantitative Traits
A. Continuous variation can arise several ways
1. From multiple genes - polygenic
2. From a single gene but there is a significant influence of the environment
a. Note: this can also arise from variable expressivity and variable penetrance
b. Second Note: some discrete traits are polygenic as well
3. From environmental influence only: in this case there is no genetic underpinning for
the trait.
B. Contributors to the phenotypic variation (VP) seen in quantitative traits
1. Genes: genetic variance, or VG
2. Environment: environmental variance, or VE
3. Total phenotypic variance VP = VG + VE + VG X E
a. VG X E is the interaction between genetics and environment
4. How do we estimate VG, which is essentially heritable variation, or heritability?
a. Response to artificial selection: from a population, select parents that exhibit an
extreme phenotype compared to the population mean. If the offspring exhibit a
phenotype shifted away from the population mean, the trait is heritable, and there
is VG
b. Parent offspring correlation: compare offspring phenotype to the midparent
phenotype. If a significant correlation exists, the trait is heritable, and there is VG
c. Twin studies: if twins raised in different environments display a similar
phenotype, the trait is heritable, and there is VG
C. Genetics of quantitative traits – determining the number of quantitative trait loci (QTL)
1. Red wheat example from the textbook
a. pigment alleles are additive: each contributes to pigmentation
b. white alleles are not additive
c. calculation of the number of genes involved:
1/4n = fraction of F2 expressing one of the extreme phenotypes