Coordinated Agricultural Project
Genomics in Tree Breeding and
Forest Ecosystem Management
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Module 2 – Genes, Genomes, and
Mendel
Nicholas Wheeler & David Harry – Oregon State University www.pinegenome.org/ctgn Quick review: Genes and genomes
In eukaryotes, DNA is found in the... – Nucleus
– Mitochondria
– Chloroplasts (plants)
Organelle inheritance is often uniparental, making it powerful for certain types of applications Figure Credit: Wikipedia Contributors, http://commons.wikimedia.org/w/index.php?title=File:Plant_cell_structure.png&oldid=45093602
www.pinegenome.org/ctgn
Chromosomes
Linear strands of DNA and associated proteins in the nucleus of eukaryotic cells
Chromosomes carry the genes and function in the transmission of hereditary information
Diploid cells have two copies of each chromosome One copy comes from each parent
Paternal and maternal chromosomes may have different alleles
Image Credit: Jane Ades, National Human Genome Research Initiative (NHGRI)
www.pinegenome.org/ctgn
Genes
Units of information on heritable traits
In eukaryotes, genes are distributed along chromosomes Each gene has a particular physical location: a locus
Genes encompass regulatory switches and include both coding and non-coding regions Genes are separated by intergenic regions whose function is not understood
Figure Credit: Darryl Leja, National Human Genome Research Initiative
www.pinegenome.org/ctgn
The central dogma of molecular biology
Figure Credit: Modified from Jeff Dean, University of Georgia
www.pinegenome.org/ctgn
Alleles
Alternative forms of a gene
A diploid cell has two copies of each gene (i.e. two alleles) at each locus
New alleles arise through mutation
Alleles on homologous chromosomes may be the same or different (homozygous vs. heterozygous)
Figure Credit: Megan McKenzie-Conca, Oregon State University
www.pinegenome.org/ctgn
Markers reflect genetic polymorphisms that are inherited in a Mendelian fashion
DNA markers 'mark' locations where DNA sequence varies (2 or more alleles)
– Such polymorphisms can vary within and among individuals (e.g. heterozygotes vs. homozygotes) and populations
Markers may be located in genes or elsewhere in the genome
– Historically, we've had too few markers to inform breeding
Genomics tools provide an almost unlimited supply of markers
www.pinegenome.org/ctgn
Mutations may take many forms
Some simple, single nucleotide mutations can totally alter a protein product by producing a frameshift. This results in a new amino acid being produced
Insertions and deletions: The addition or loss of one or more nucleotide(s) in coding sequence www.pinegenome.org/ctgn
Figure Credit: Modified from Lewin, 2000.
Single Nucleotide Polymorphisms
(SNPs) embedded within a DNA sequence
DNA sequences are aligned
Polymorphic sites are identified
Haplotypes (closely linked markers of a specific configuration) are deduced by direct observation or statistical inference
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* atggctacctgaactggtcaactcatcgaaagctaa atggctacctgaactggtcaactcatcgaaagctaa atgcctacctgaactggtcaactcatcgaaagctaa atgcctacctgaactggtcaactcatcgaaggctaa atgcctacctgaactggtcaacacatcgaaggctaa Figure Credit: David Harry, Oregon State University
www.pinegenome.org/ctgn
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Single Nucleotide Polymorphism (SNP)
SNP
Tree 1
Tree 2
Tree 3
A C G T G T C G G T C T T A
A C G T G T C A G T C T T A
Maternal chrom.
A C G T G T C G G T C T T A
A C G T G T C G G T C T T A
Maternal chrom.
A C G T G T C A G T C T T A
A C G T G T C A G T C T T A
Maternal chrom.
Tree 1 is heterozygous
Paternal chrom.
Paternal chrom.
Trees 2 and 3 are homozygous
Figure Credit: Glenn Howe, Oregon State University
www.pinegenome.org/ctgn
Paternal chrom.
The genome
An individual’s complete genetic complement
For eukaryotes, a haploid set of chromosomes
For bacteria, often a single chromosome
For viruses, one or a few DNA or RNA molecules