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

Molecular Structure Cellular Function Organismal Evolution Population

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)

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

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

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

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

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

Figure 26.9 Evolution of paralogous and orthologous genes

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

Developmental Genetics

Bithorax Mutation

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)

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