BIOA01H3 Lecture Notes - Lecture 12: Sympatric Speciation, Asexual Reproduction, Nondisjunction
13 May 2018
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BIOA01
LEC 12: Speciation and Variation
SEPT 29, 2015
1. Genetic Isolation (no gene flow)
→ 1.1: Allopatric Speciation (most common)
• Physical barrier divides a pop.
• A. Vicariance
- example: formation of Isthmus of Panama = vicariance event for
MARINE animals
- closely related animals found on Pacific and Caribbean side
- pairs of species on either side of land bridge
• B. Dispersal
- dispersal among islands can lead to REPEATED divergence
- Ex: Kingfishers on mainland New Guinea (varies on nearby
islands→ closely related but diff. subspecies
- Species cluster: closely related species or subspecies descended
from a RECENT ancestor
- Ex: Caribbean Anolis Lizards
→ Sympatric speciation
• Subgroups form within a pop. In the same geographic region
• Specialization in subgroups reduce gene flow
A. Host races
- different variants favour distinct hosts
- Ex: Hawthorn fruit (more nutritional for maggots but more likely
to be parasitized) and apples (less nutritional but less likely to be
parasitized) → equally good for them
B. polyploidy
more than 2 pairs of homologous chromosomes
- ancestral state for eukaryotic organimss is two copies of chromo
(diploid)
- gametes have one set of chromo. (haploid)
- two routes→ autoplyploidy & allopolyploidy
autopolyploidy → adults give rise to gametes; in some there is a mutation that
causes non-disjunction ; create triploid offspring that cannot produce gametes →
meiosis does not continue
- ***if gamete self-fertilizes, the produces two 4 offspring allows
meiosis to continue
- if organisms can self-fertilize and asexually reproduce, fertile
offspring is the result
allopolyploidy
- species 1 and species 2 are able to produce gametes
- the gametes hybrdidize a zygote
- then produce offspring that may be viable but might be sterile
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Document Summary
Sept 29, 2015: genetic isolation (no gene flow) 1. 1: allopatric speciation (most common: physical barrier divides a pop, a. vicariance. Example: formation of isthmus of panama = vicariance event for. Marine animals closely related animals found on pacific and caribbean side. Pairs of species on either side of land bridge: b. dispersal. Dispersal among islands can lead to repeated divergence. Ex: kingfishers on mainland new guinea (varies on nearby islands closely related but diff. subspecies. Species cluster: closely related species or subspecies descended from a recent ancestor. Sympatric speciation: subgroups form within a pop. In the same geographic region: specialization in subgroups reduce gene flow, host races. Ex: hawthorn fruit (more nutritional for maggots but more likely to be parasitized) and apples (less nutritional but less likely to be parasitized) equally good for them: polyploidy more than 2 pairs of homologous chromosomes. Ancestral state for eukaryotic organimss is two copies of chromo (diploid)
