BIOL 2040 Lecture Notes - Lecture 7: Genetic Drift, Allele Frequency, Population Genetics
3 May 2018
School
Department
Course
Professor
Gene Flow and Genetic Drift – Population Genetics
October 13, 2015
Gene Flow
• Causes:
o Pollen – haploid gene flow
o Seeds – diploid gene flow
o Ballooning spiders get blown around
by wind
o Tumbleweeds – winds blow seeds
• Migration of adult gametes migrate
• Ex. A1-600, A2-200 1-m
o Frequency of A1 before = .75
o After migration….
o Addition of 100 A1 AND 400 A2 m (migrants)
▪ Frequency of A1 in migrants: 0.2
o Migration rate: m= (100+400)/(100+400+600+200) = 0.38
o After migration, p=7/=.
o p=p-m)+pm(m)
o
• Ex. Unidirectional migration from a continent to an island – no selection; all fitness equal
o On continent:
▪ A1A1: .04, A1A2: 0.32, A2A2:0.64
▪ Therefore: pm=.2
o On island:
▪ A1A1: 0.35, A1A2: 0.5 , A2A2: 0.25
▪ Therefore, p= 0.5
o Migration rate = 0.1
o P=.-0.1)+0.2(0.1)=0.47
o The change of p = - .03
o With only migration present, the receiving population will end up with same
frequencies as donor population (ex. Island will have same as continent)
• Conclusions with Migration ONLY:
o Migration acting alone will equalize allele frequencies
o If unidirectional, then recipient population will eventually end up with the allele
frequencies of source population
Selection - usually occurs in zygotesadults
• Selection followed by migration… p=fA & q=fA
o After selection…
▪
▪
o After migration…
▪
▪
o A1 is not completely lost because of the presence of migration (may be source of
genetic variation)
p*=f(A1A1)w11 +1
2f(A1A2)w12
w
q*=
1
2f(A1A2)w12 +f(A2A2)w22
w
¢
p =p*(1-m)+(pm)m
¢
q =q*(1-m)+(qm)m
GAMETES
ZYGOTES
ADULTS
Fertilization
Meiosis
Migra on
(generally in H-W !!)
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Gene flow and genetic drift population genetics. Gene flow: causes, migration of adult gametes migrate, ex. Frequency of a1 in migrants: 0. 2: migration rate: m= (100+400)/(100+400+600+200) = 0. 38, ex. Island will have same as continent: conclusions with migration only, migration acting alone will equalize allele frequencies. If unidirectional, then recipient population will eventually end up with the allele frequencies of source population. Selection followed by migration p=f(cid:523)a(cid:883)(cid:524) & q=f(cid:523)a(cid:884)(cid:524: after selection , after migration . P = p * (1- m) + ( pm )m. Q = q * (1- m) + (qm )m. 2 f (a1a2)w12 f (a1a1)w11 p* = q* = 1: a1 is not completely lost because of the presence of migration (may be source of genetic variation) Selection and migration act in opposing directions: ex. Northern water snake nerodia sipedon: mainland: Islands: many unbanded, many bask on rocks, unbanded have a higher survival rate, banding allele is dominant islands are receiving allele from mainland.
