evoltuion - types of selection notes
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Evoltuion - types of selection
Monday, November 9, 2015
2:58 M
rocess of natural selection -
! main in"rediants from natural selection
#ariation of traits in population
$ %eedin" out process
&ome t'in"s selected for and some t'in"s selected a"ainst
(o ma)e t'at selection - 'as to be some basis
*i+erences amon" individuals amon" population
&ome sort of stru""le for survivle
(ypical in natural %orld
$ll sorts of problems or"anisms encounter
(emperature and so on
esult of t'is stru""le
Not all individuals survive
('ird component
'at %e come to )no% as survival of t'e .ttest
/oo) at t'e individuals t'at survive and compare t'em to indiduals %'o didntsurvive posses traits
itter individuals %'o survive - .tter individuals
(raits - individual traits to survive - "enetic basis
ass t'em o+ to o+sprin" - o+sprin" also e'ibit t'ose traits
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3dentify t'ose )ey in"rediants
#ariation - in t'is mot' population
4onsists of blac) peppered form
#ery important t'in" to point out
re-eistin" variation
Eits in population if anyt'in" else is "oin" on or not
$t time polution occurred some blac) forms of mot' but most 'ad peppered
&tru""le for survile
('is case - birds tryin" to eat mot's
Not noticed by birds and arent eaten
/o%er ri"'t - tree trun) after polution 'as occurred
*ar) form - pretty %ell camo6o"ued but peppered form stands out
7irds see peppered form and consume it
7lac) form better to .ttest
eppered form removed
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4oloration pattern determined by sin"le "ene ma)essome blac) some ppered
+sprin" carryin" "ene for dar) form
(al)in" about selection for blac) form of "ene or peppered form
ocusin" on sin"le trait
&election acts on individuals - all its "enes
&ome 'ave "ood some 'ave bad
Not sin"le trait determines 'o% .t you are
n avera"e individuals %'o 'ave "reater number of "ood alleles do beter t'anindivuduals %'o 'ave less
3ndividuals %'o 'ave "reater - put "ood alleles into "ene pool
More "ood alleles "et into "eneration t'an bad alleles
More "ood alleles t'an previous "eneration
ound t'at population 'ave lar"er number more .t and better to cope and muc'better adapted t'an ot'er individuals
irst in"rediant - variation
#ariation amon" individuals %it'in population
'at is responsible for variation
#ary a%are of %'at it is
/oo) at people %e )no%
Not same as us
*i+erent c'aracteristics
#ariation acted upon by natural selection
'at is responsible
'y arent individuals more similar
Main source - in t'e process of "ametes and seual reproductions
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&'uin" of "enetic matirial
ecombination
or eample
3ndividual ma)es "ametes by meiosis
;ametes made by individual
None are t'e same
'y are t'ey di+erent
'en meiosis occurs - independent assortment of c'romosome
'en you ma)e "ametes
;ametes 'ave 'alf number of c'romosomes
<no% %'en you ma)e t'em
ne representative from eac' 'omolo"ous pair of c'romosomes
7ut eac' one you ta)e is random
/ots of combinations in "ametes
4ross over %it' eac' ot'er
&'arin" e'an"e of "enetic information
urt'er s'ues "enetic material
Made "ametes very di+erent 0 matin" partner also ma)in" "ametes di+erent
(o ma)e individual combine "ametes
4'ances you loo) li)e brot'er or sister are slim
Made by parents eac' di+erent possible of combinin" very di+erent as %ell
/ots of opportunities for recombination
3mportant source
=ltimate source
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Mutation
>o% c'an"es 'appen to "enes
Mutations c'an"e dna messa"e in some %ay
Most are bad
&ome are neutural - doesnt c'an"e function
4ases %'ere c'an"es are "ood
;rabs and puts t'em up to 'i"'er fre?uency
(ypes of variation t'at eist in population
Natural selection acts on t'em - outcome dependent on type involved
@ualitative
(raits - consist of eit'er 2 states
>ave trait or dont
*etermined by sin"le "ene
Earlobe attac'ment
Not'in" in bet%een
ne t'in" or t'e ot'er
(ypes of variation called ?uantitative or continuous variation
4onsists of all de"redations in bet%een
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Many traits or"anisms 'ave fall under t'is cate"ory
(raits 'umans 'ave
&in"le "ene and come in one state or ot'er
>o% tall
'at i?
&)in color
Many "enes
4ontinuous variation
Not tall or s'ort - everyt'in" in bet%een
Not Aust 'i"' or lo% - a lot in bet%een
Muc' colors from dar) to li"'t
Number of t'in"s not Aust t'ree "enes
4ontribution on "enes
Eac' produces a little bit of melonin
&um of contribution of all contributes to 'o% dar) your s)in is
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$lleles eit'er open or dar) circle
*ar) circle - melonin production
/oo) at "rap' - all di+erent )inds of variation in t'is population
3ndividuals on left - li"'t s)in
3ndividuals on ri"'t - all dar) type - dar)est s)in
an"e of t'in"s inbet%een
4ontinous variation and traits determined by many "enes
B types t'at can occur %it' some variation
=pper picture
ri"inal startin" population
n y ais fre?uency
n ais - bunc' of mice- li"'t colored to dar)er colored
opulation - li"'t in color some dar) in color
>ump in middle
Most individuals are some%'ere in t'e middle
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opulation li)e t'is
/oo) at mice
&ome dar)er some li"'ter
'at if natural selection %ere to opperate on t'is population
3ndividuals dar)er - did better t'an li"'ter in color
'at %e 'ave t'en - type of selection - direction selection
/o%er left 'and panel - %'at result %ould be
*otted blue line - ori"inal population
&election for dar)er colored individuals - be more li)ely to leave o+sprin" - t'eir
o+sprin" "iven dar) alleles from parents "o out many "enerations - see populationcurve s'ifted to one side
3ndividuals on avera"e muc' dar)er t'an ori"inal population
1 direction selection - mean of population moves in particular direction
Mice eample moves from medium dar) to even dar)er fur
'ats 'appenin" - c'an"e in value of trait over time
&een before peppered mot'
*irection selection - peppered to primarily blac) colored mot's
(%o di+erent )ids of variation
@ualitative - t'in"s can be in one state or ot'er or continus variation
@ualitative - direction selection -
;oin" to eliminate bad allele and . on best allele
eppered mot' story - allele t'at determined blac) and one t'at determined pepper
$s peppered mot's dies o+
4'an"e to potentially all alleles %ill be of blac) form - etreme possibility - cant "oany fart'er
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*irectional selection on ?uanitative traits
3ts possible after many "enerations - avera"e value eceed anyt'in" present inpopulation
@uantitative traits - many "enes
$lleles of all t'ose "enes
Many "enerations of selection
More and more of t'ose "enes 'ave "ood allele
(a)es time for t'at to 'appen
;et to a point %'ere all "enes 'ave "ood alleles ori"inal population 'ad all "oodallele
Eample 'avin" to do for bristle number on drosop'ila
fruit 6ies
ri"inal population - re"ular old population - count number of bristles - .nd is t'aton avera"e individuals 'ave !0 bristles
&ome t'at 'ave as fe% as B0 some as many as 50
urple s'ape - re?uency of t'ose %it' di+erent bristle numbers
*o a selection eperiment
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$ lot of bristles - pull aside and let t'em mate
7lue ."ure on ri"'t - %'at you %ould "et after certain number of "eneration
Mean around 90 bristles
n avera"e in ori"inal about !0
No% %e are up to 90
Every individual 'as more bristles t'an 'i"'est in ori"nal population
3n t'is eperiment selected individuals %it' fe%est bristles
Number of "enerations c'oose ones %it' fe%est bristles
/o% selected population
$vera"e little above 10
$nd even one %it' 'i"est number is lo%er t'an t'e B0 from ori"inal population
&election on traits determined by many "enes selection ta)e population fart'er t'anyou %ould epect
/imits to natural selection
&elections actin" on "eneration after "eneration
Eliminate all bad alleles - and selection %ould stop
'y 'avent t'at 'appened
>uman population - lot of bad alleles 6oatin" around
4ystic .brosis sic)le cell anemia
'y 'asnt selection eliminated t'em
ecessive alleles - bad allleles
(%o copies in individual - 'ave disease
Not "ood as individual %'o doesnt
&election 'as a problem in "ettin" at bad alleles and eliminatin" t'em
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>eteroCy"ote - dont s'o% recessive allele
nly s'o% dominant allele
$lt'ou"' t'ey carry bad allele
&election - loo) li)e dominant individual
ecessive 'ide in 'eteroCy"ote
3mpossible to "et all bad alleles out
$lleles seem to be bad in one contet "ood in anot'er contet
opulation of united states
7lac)s in us 'ave 'i"'er rate t'an %'ites do
e need to loo) at africa %'ere blac)s in t'e united states come from
3nterestin" pattern
;rey s'ado%ed area
'ere t'e maleria parasite very common
Malaria - millions people die every year
3n places %'ere malaria common
>i"' fre?uency of sic)le cell allele
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$t .rst "lance- very odd
(urns out t'at malaria paracite attac)s red blood cell
&ic)le cell also a+ects red blood cell
>eteroCy"ous for sic)le cell allele
esist maleria t'an t'ose %'o dont 'ave t'is allele
>i"' incedent of sic)le cell "ives you resistance of alllele
&laves in nort' america
&ic)le cell alllele
Nort' america no maleria for advanta"e
&ee over time t'is allele slo%ly eliminated
>i"'er in blac) t'an %'ite
/o%er panel on ri"'t
3lustrates stabeliCin" selection
Eliminate bot' etremes
3n t'is case
3ndividuals li"'ter and dar)er dont survive as %ell
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Eliminatin" dar)est and li"'test ones and population stabeliCed on inbet%eenp'enotype
;ood eample %it' re"ard to 'uman birt' %ei"'t
#ery small very lar"e babies
&mall babies - diDculty survivin"
/ar"e - more problems t'an babies in t'e middle on avera"e
n avera"e babies -8 pounds
Fello% tells you somet'in" about %'at types of birt' %ei"'ts you .nd
F ais - percent of population
n avera"e babies -8 pounds
#ery small - lo%er
&ome babies 9 10 11 pounds
'ite - percent mortality %it' babies of di+erent birt' rate
-8 do%n - mortality increases
-8 to 9, 10, 11 mortality also increases
7ot' lo%est and 'i"'est %ei"'t - tend to be eliminated from population
&tabeliCe about -8 pounds
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7ot' etremes are selected but t'in"s in middle selected a"ainst
#ery rare
/i"'test colored do %ell
*ar)est do %ell
3n bet%een dont do %ell
*isruptive
us'es population to eit'er side
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7lac) bellied seed crac)ers
May not be obvious to you
7ut bidr on left
7illbee) not as %ide as t'e bee) on t'e ri"'t
/oo) at population .nd t'at rat'er bein" ran"e of bill siCes from small to lar"e
('ey actually Aust 2 classes
&mall billed and ar"er billed
/oo) at %'at t'ey are eatin"
&ome smaller softer seeds and also some bi""er 'arder seeds
&mall bills - smaller seeds
/ar"e bills - lar"er seeds
Medium bill - doesnt 'elp you %it' eit'er
&peciation
&in"le species to 'ave 2 di+erent species of or"anisms
ossible %ays speciation can come about
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('rou"' disruptive selection
;eneral idea
it'in population
ne etreme and ot'er etreme
Many "enerations - smaller billed becomes one species
$nd lar"er becomes di+erent species
ont say more no%
(ac)le amon" speciation