Polyploidy I. Types of polyploidy A. Autopolyploidy: more than 2 genetically identical genomes B. Allopolyploidy: combines the genomes of more than one.

Presentation on theme: "Polyploidy I. Types of polyploidy A. Autopolyploidy: more than 2 genetically identical genomes B. Allopolyploidy: combines the genomes of more than one."— Presentation transcript:

1 Polyploidy I. Types of polyploidy A. Autopolyploidy: more than 2 genetically identical genomes B. Allopolyploidy: combines the genomes of more than one species C. Intermediate situations, e.g. segmental allopolyploids D. Ancient polyploidy followed by chromosomal repatterning and restoration of diploid-like chromosome behavior "diploidization"

2 II. Frequency of Polyploidy A. 30-35% (Stebbins) - 70-80% (Lewis) of angiosperms depends if only "multiples" within a genus are counted or if n > 10 is counted B. Support for higher estimate 1. Smaller stomata in Miocene fossils supports higher estimate 2. Evidence for genome duplication Arabidopsis n = 5 C. Varies across taxonomic groups e.g. Common in ferns [20% in North America] but not conifers

3 Duplicated sections of the Arabidopsis genome

4 III. Genetics of Polyploids A. Allopolyploidy & Isozymes 1. fixed heterozygosity 2. disomic inheritance AAaa X AAaa - > AAaa

5 B. Autopolyploidy & Isozymes 1. subset of progenitor’s alleles 2. tetrasomic inheritance AAaa X AAaa - > 1 AAAA 8 AAAa 18 AAaa 8 Aaaa 1 aaaa e.g. Tolmiea menziesii

6 diploid SkDHPGM TPI PGI Tolmiea menziesii

7 IV. Multiple origins of polyploids A. Different fixed heterozygote genotypes in allotetraploids B. Different cpDNA haplotypes C. Different ITS repeats through concerted evolution D. Documented in Tragopogon, Brassica triangle, various ferns E. results in polyphyletic species, if independent polyploids are interfertile

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9 2n 4n 2n 4n 2n 4n

10 Hybridization and Introgression hybridization = F1 “crosses between genetically differentiated taxa” introgression = F2 backcrosses “movement of genes between species (or other well- marked genetic populations) mediated by back- crossing”

11 I. Hybrid zones A. Observed in many species Longstanding questions: 1. primary speciation or secondary intergradation? 2. Source of new species or just "evolutionary noise" ?

12 B. Ecology of hybrid zones 1. Often in intermediate habitats 2. Often in disturbed habitats

13 L. leucophyllus × sericeus L. sericeus var. egglestonianus L. leucophyllus L. sericeus

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15 L. latifolius var. latifolius × sericeus = L. latifolius var. thompsonianus

16 3. Conservation concerns over loss of endemics due to hybridization with a widespread taxon e.g. Norway spruce swamping Serbian spruce Penstemon parryi used in post-fire restoration & highway planting

17 II. Diploid Hybrid Speciation considered uncommon, < 10 documented cases best known in Helianthus A. fertile F1 B. Stabilization of hybrid segregants C. How does it become reproductively isolated?

18 1. postmating: recombinational speciation via chromosomal rearrangements 2. premating: ecological divergence e.g. habitat or pollinator D. Polarity assessment can be problematic, because ploidy level cannot be used as a clue to parentage

19 III. Introgression "genetic exchange between hybridizing species" A. Asymmetry of gene flow 1. Nuclear genes transferred, cpDNA not e.g. Long-distance pollen movement 2. Chloroplast capture: cpDNA transferred, not nuclear genes 3. potential for cytoplasmic incompatibility and reproductive isolation (Levin, Syst. Bot. 28:5-11, 2003)

20 Morgan, D.R. 2003. Systematic Botany 28: 179–190. nrDNA External Transcribed Spacer (ETS) Sequence Data, Reticulate Evolution, and the Systematics of Machaeranthera (Asteraceae) Machaeranthera

21 homoploid reticulation = introgression

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23 Machaeranthera gracilis 2n = 4 M. tanacetifolia J. Semple