Transcript B 1 - 國立交通大學

一、參選類別（請勾選）：
■「學士班必修課程與全校性共同課程」候選人
□「其他(學士班選修及研究所) 課程」候選人
四、近二年任教之學士班必修課程與全校性共同課程
學年度 學期 當學期
課號
課程名稱
開課單位
開課對象
修課
(系級班別) 人數
97
1
1495
普通生物學（一）
生科系
生科系大一 59
98
1
1557
普通生物學（一）
生科系
生科系大一 63
國立交通大學生物科技學院
助理教授 林勇欣
The “mystery of mysteries” that captivated Darwin is
speciation, the process by which one species splits into two or
more species
Speciation fascinated Darwin (and many biologists since)
because it is responsible for the tremendous diversity of life,
repeatedly yielding new species that differ from existing ones
Speciation explains not only differences between species, but
also similarities between them (the unity of life)
Speciation also forms a conceptual bridge between
microevolution, changes over time in allele frequencies in a
population, and macroevolution, the broad pattern of
evolution over long time spans
Chapter 23 – microevolution
Chapter 25 – macroevolution
In this chapter, we will explore the “bridge” – the mechanisms
by which new species originate from existing ones
First, we need to establish what we actually mean when we
talk about “species”
The tephritid fly has distinctive dark bands on its wings. When
disturbed, the fly holds its wings perpendicular to its body and
waves them up and down. Entomologists had noticed that this
display seems to mimic the leg-waving, territorial threat display
of jumping spiders.
• The first step in any evolutionary analysis is to phrase the
question as precisely as possible
• In this case: Do the wing markings and the wing waving of the
fly mimic the threat displays that jumping spiders use on each
other, and thereby allow the flies to escape predation?
•
•
When the researchers tested treatments A, C, and E
against other predators, all of the test flies were captured
and eaten
There was not even an appreciable difference in time-tocapture among the three treatment groups
The initial allele frequencies are 0.01 for B1 and 0.99 for B2
A general treatment of selection
If there are two alleles, B1 and B2, with frequencies p and q
We incorporate selection by imagining that
B1B1 zygotes survive to adulthood at rate w11;
B1B2 zygotes survive at rate w12; and
B2B2 zygotes survive at rate w22
All individuals that survive produce the same number of offspring
We can therefore refer to the survival rates as fitnesses
The average fitness for the whole population, w, is given by the
expression: w = p2w11 + 2pqw12 + q2w22 ≦ 1
A general treatment of selection
The average fitness for the whole population, w, is given by the
expression: w = p2w11 + 2pqw12 + q2w22 ≦ 1
The new frequencies of the genotypes are:
B1B1
B1B2
B2B2
p2w11
2pqw12
q2w22
w
w
w
The new frequency of B1 is
p 2 w11  pqw12
p' 
w
The new frequency of B2 is
pqw12  q 2 w22
q' 
w
A general treatment of selection
It is instructive to calculate the change in the frequency of allele
B1 from one generation to the next
This value, ∆p, is the new frequency of allele B1 minus the old
frequency of B1:
p 2 w11  pqw12
p  p' p 
p
w
p 2 w11  pqw12  p w

w
p

pw11  qw12  w
w


The change in the frequency of allele B2 from one generation to
the next is
q
q 
pw12  qw22  w
w


An algebraic treatment of selection on recessive and
dominant alleles
frequencies
fitness
AA
p2
wAA = 1
Aa
2pq
wAa = 1
aa
q2
waa = 1 + s
Where s called selection coefficient
pqwAa  q 2 waa
pqwAa  q 2 waa
q1  sq 
q' 
 2

2
p wAA  2 pqwAa  q waa
1  sq 2
w
If a is a lethal recessive, then s is equal to -1
q1  q 
q1  q 
q
q' 


2
1  q 1  q  1  q 
1 q
An algebraic treatment of selection on recessive and
dominant alleles
frequencies
fitness
AA
p2
wAA = 1 + s
Aa
2pq
wAa = 1 + s
aa
q2
waa = 1
p 2 wAA  pqwAa
p 2 wAA  pqwAa
p1  s 
p' 
 2

2
p wAA  2 pqwAa  q waa 1  2sp  sp 2
w
If A is a lethal dominant, then s is equal to -1
A lethal dominant is eliminated from a population in a single
generation
p1  1
p' 
0
2
1 2 p  p
An algebraic treatment of selection on recessive and
dominant alleles