BIOL 2040 Lecture Notes - Lecture 12: Medium Ground Finch, Large Ground Finch, Vulpes
3 May 2018
School
Department
Course
Professor
Quantitative Genetics: Selection and Evolution
November 5, 2015
Correlated Evolution
• Slight variation in one part through natural selections causes other modifications
unintentionally
• Therefore, traits are not independent of each other
• Occurs when selection on one trait also causes an evolutionary response in another trait
• Cause: genetic correlation between traits
• Genetic Correlations arise from:
o Pleiotropy *most important
▪ Single locus affects 2 or more traits
▪ Positive correlation: genotypes affect 2 traits in the same direction
▪ Negative correlation: genotypes affect 2 traits in opposite directions
o Linkage Disequilibrium
▪ Ex. Gene A affects only tooth height. Gene B only affects tooth width. Allele 2
increases trait value in each locus
• The alleles that make one trait larger tend to occur with alleles that
make the other trait larger
• Result: positive genetic correlation between tooth width and height
▪ Ex. Medium Ground Finch
• When selected for deeper beaks other traits including body size and
beak width also changed
Correlated Response to Selection in One Rate
Ex. Silver Fox (Vulpes vulpes)
• Direct selection for domestication based on friendly behaviour – Dmitri Belyaev
• Began in Siberia, 1959 for over 40 years
• Found: social cognitive ability also evolved (including point and gaze)
• Recently: number of correct choices was made by point and gaze cue
o Number of domesticated foxes had same success as dog puppies
o Experimental foxes has a larger success than control foxes
• Correlated Evolution:
o Direct selection for domestication ONLY. Traits that also evolved:
▪ Behavioural
• Social cognitive ability
• Whimper to attract attention
• Sniff and lick caretakers
• Wag tails
▪ Morphological
• Coat colouration
• Floppy ears
• Short or curly tails
• Shape of jaws, skull, teeth
• Lost musky fox cell
▪ Physiology
• Lower adrenaline
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Document Summary
Allele (cid:498)2(cid:499: the alleles that make one trait larger tend to occur with alleles that, linkage disequilibrium increases trait value in each locus make the other trait larger, result: positive genetic correlation between tooth width and height, ex. Medium ground finch: when selected for deeper beaks other traits including body size and beak width also changed. Selection on multiple traits: medium ground finch on isla daphne major, drought of 1976-1977, selection on beak depth: deeper is more fit, but beak width and depth are genetically correlated. If we looked at one trait at a time conclude that selection favours: In 2 species of darwin"s finches, selection acted different on the two populations: depends on the selection differential (s, selection may fluctuate due to environmental conditions. Character displacement: one species causes character evolution in another due to competition: example, native: medium ground finch.
