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Lecture 12

BIOA01H3 Lecture Notes - Lecture 12: Genetic Drift, Speciation, Phylogenetic TreePremium

Biological Sciences
Course Code
Maydianne Andrade

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BIOA01H3: Unifying Principles – Life on Earth – Lecture 12: Speciation
Population of one species become genetically isolated (no gene flow)
“Diverse from each other due to genetic drift and mutations
Population may become reproductively isolated can be recognized as distinct species of:
are unable to interbreed successfully; have distinct morphological characters; from
independent branches on a phylogenetic tree
Physical barrier divides a population
Two different geographic locations
Well-expected (has happened on a wide range of taxa)
Dispersal (founder effect can cause this) ex. kingfishers on mainland New Guinea,
genetic are different
Subgroups from within a population occupying the same geographic region
Does not have to be a physical barrier: speciation or genetic changes in subgroups
reduce gene flow
A. hosting races (adaption to different host) different variance
B. Polyploidy (more than two pairs of homologous chromosome) ex. apple hawthorn
C. Chromosome arrangement
Ancestral state for eukaryotic organism in two pairs of chromosomes = 2n (diploid)
Gametes (formed by meiosis) have one set of chromosomes = n (haploid)
More common in plants then other organisms because self-fertilization is common in
Two Paths: Auto polyploidy: Spontaneous non-distinction of chromosomes at meiosis,
result in gametes with doubles chromosomes Allopolyploid: Hybridization of species is
followed by chromosome duplication during mitosis ex. evolution of wheat
Chromosome Rearrangements:
Result in variation in gene expression, in the order of gene located in chromosome
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