1. (Quantitative, Evolution, & Development)
Genetics:
At the Crossroads
(Quantitative, Evolution, & Development)
(CHAPTERs 23, 24 & 26- Brooker Text)
December 11, 2007
BIO 184
Dr. Tom Peavy

2. Molecular
Structure
Cellular
Function
Organismal
Evolution
Population

3. Quantitative genetics (the study of traits that can be described numerically) is important for two reasons
1. Most of the key characteristics considered by plant and animal breeders are quantitative traits
2. Many of the traits that allow a species to adapt to its environment are quantitative traits
Discontinuous vs. continuous traits
(discrete states) (continuum of variation)

4. POLYGENIC INHERITANCE
Most quantitative traits are polygenic and exhibit a continuum of phenotypic variation
Polygenic inheritance refers to the transmission of traits that are governed by two or more genes
The locations on chromosomes that affect the outcome of quantitative traits are called quantitative trait loci (QTLs)
QTLs may contain many genes
Some or all of which may affect quantitative traits

5. QTLs Are Now Mapped by Linkage to Molecular Markers
Molecular markers, such as RFLPs, are now being used as reference points along chromosomes
These genetic markers have been used to construct detailed genomic maps
These maps make it easier to determine the number of genes that affect a quantitative trait
Detailed genomic maps have been obtained from
Model organisms
Organisms of agricultural importance

6. The data are analyzed by computer programs that can statistically associate the phenotype (e.g. fruit size) with the molecular marker

8. Differences in nucleotide sequences are quantitative
Molecular genetics has greatly facilitated our understanding of speciation and evolution
Differences in nucleotide sequences are quantitative
They can be analyzed using mathematical principles in conjunction with computer programs
Thus, evolutionary changes at the DNA level can be objectively compared among different species
This will establish evolutionary relationships
Furthermore, this approach can be used to compare any two existing organisms
No matter how greatly they differ in their morphologies
E.g., Humans and bacteria; or plants and fruit flies

9. Homologous Genes are Derived from a Common Ancestral Gene
Two genes are said to be homologous if they are derived from the same ancestral gene
Genes can exhibit interspecies homology and intraspecies homology
Orthologous genes or orthologs are homologous genes found in different species
Paralogous genes or paralogs are homologous genes found within a single species
A gene family consists of two or more copies of homologous genes within the genome of a single organism

10. Figure 26.9 Evolution of paralogous and orthologous genes

11. Figure 26.10 The current model links all life on our planet
Three main evolutionary branches
Figure 26.10

12. Developmental Genetics

13. Bithorax Mutation

14. Evolution of Development (Evo-Devo)
Homeobox Genes first discovered in Drosophila
(Gehring and Kaufman, 1983)
HOMEOBOX = DNA sequence found within genes involved
in the regulation of development (morphogenesis) of
animals, fungi and plants.
(Homeobox gene family).
A particular subgroup of homeobox genes are the Hox genes,
= Hox cluster (also called Hox complex).
= function in patterning the body axis
(determine where limbs and other body segments will
grow in a developing fetus or larva)

23. That's All Folks!