BIOL 2040 Lecture Notes - Lecture 17: Sympatric Speciation, Allopatric Speciation, Hybrid Speciation
27 Apr 2018
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Lecture 17 - Speciation (end), Novel Traits
April 11, 2018
4:01 PM
Allopatric speciation: physical barrier separates a population into two. It's the most common speciation
that occurs - they eventually contact each other again (secondary contact)
Sympatric speciation: non-physical barrier separates a population into two. Generally under restrictive
conditions - chromosomal re-arrangement aids in the barrier.
Aneuploidy in humans and apes
• Human chromosome #2 is similar to a chromosome in the gorilla and the chimpanzees
o Human chromosome #2 looks like part of the chromosome in gorilla and chimpanzees fused
together
• If the human chromosome #2 was fused from gorilla and chimp chromosomes:
o There would be a telomere and two centromeres in the middle
o A chromosome cannot have 2 active centromeres so one of them must be silenced
• Prediction holds - the exact fusion site can be found on the chromosome (due to the two bits of
telomeres that fused into one), and a silenced centromere was found on the chromosome
Novel Traits
• Origins of New genes and traits
Back to the sunflowers - how did the hybrid get so different?
• Petals are much more different than the parents
• Range of variation are outside of parents
• Recall additive quantitative genetics:
o Each "capital" allele increases the trait by a set amount (additive variation) so all hybrids fall
in between parents
• Recombination also produces extreme phenotypes - some of the offspring may fall outside the
parental range and can be selected against/for
o If parents (as heterozygotes) have a mix of alleles from its previous homozygotic parents,
their offspring are able to have a full range from one extreme to the other)
find more resources at oneclass.com
find more resources at oneclass.com
• Mapping results in sunflower:
o In some genes, it's more similar to annuus - in other genes, it's more similar to petiolaris
• Evidence that the hybrid has genes from both species
o The H. anomalus combines alleles from its' parents to achieve an extreme phenotype and
colonize an extreme environment (it can survive in drier areas than parents)
• Hybrid is different from either parent because it rearranged the different genes from
parents, giving the hybrid the ability to adapt to novel habitats (shuffling gene order
helps)
• Also prevents it from breeding with parents
Novel traits in hybrid species of sunflower
• Derived from the reorganizing of existing genetic variation present in the parental species
• Some other hybrids thrive in shifting sand (sand dunes), others thrive in deep (stable) sand, and
others in salt environments
Re-Assortment and the evolution of new Influenza Strains
• Influenza - like HIV, it attacks the cell in respiratory tract and injects its RNA (its genetic material)
into the cell
o Has surface proteins which act like GP120 on HIV
o Unlike most viruses, influenza has eight separate RNA molecules in its genome
• Single infection: All 8 RNA molecules are injected into the cell, they replicate, and are packaged
into daughter cells and sent out
o Nothing wrong with that
• Double infection: Two different virions infect the same host
o This isn't common
o When repackaging RNA molecules into daughter cells, the 2 different RNA groups could be
mixed
• Daughter cells may get a mixed package from both virions, and the two different sets
of RNA molecules may create novel traits that may be more deadly to the host
o This is when you worry about it
Re-assortment in the recent (2009) H1N1 virus
• Genes in influenza could be traced to different branches in a phylogeny
• H1N1 in 2009 - some RNA particles comes from different branches of influenza
o The different RNA particles appear to have come from different branches
Concerns over Influenza
• Current human flu strains: can infect humans and are relatively survivable
• Current bird flue strains: cant easily infect humans and are very severe when they do
• A double infection could lead to re-assortment (recombination) of genes and that new strain could
infect humans and be highly virulent
o This process is conceptually the same as hybrid speciation
Release, reorganize, reuse
• Release: from selective constraint of original function
• Reorganize: alter gene sequence or phenotype
• Reuse: for a new or additional function
• Recombination: hybrid speciation, influenza reassortment
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Allopatric speciation: physical barrier separates a population into two. It"s the most common speciation that occurs - they eventually contact each other again (secondary contact) Sympatric speciation: non-physical barrier separates a population into two. Generally under restrictive conditions - chromosomal re-arrangement aids in the barrier. Aneuploidy in humans and apes: human chromosome #2 is similar to a chromosome in the gorilla and the chimpanzees, human chromosome #2 looks like part of the chromosome in gorilla and chimpanzees fused together. Novel traits: origins of new genes and traits. If parents (as heterozygotes) have a mix of alleles from its previous homozygotic parents, their offspring are able to have a full range from one extreme to the other: mapping results in sunflower: Novel traits in hybrid species of sunflower: derived from the reorganizing of existing genetic variation present in the parental species. Some other hybrids thrive in shifting sand (sand dunes), others thrive in deep (stable) sand, and others in salt environments.
