Transcript 第二週

Chapter 2
Genetics and Ecology
© 2002 by Prentice Hall, Inc.
Upper Saddle River, NJ 07458
Chapt. 02
Outline
• Species occurrence due to evolutionary
past.
• Mutations and chromosomal
rearrangements result in a wide variety of
species on earth.
#2
Chapt. 02
Outline
• Genetic variability can be measured by
allozymes or DNA sequencing.
• Mechanisms for reductions in genetic
variability in populations.
#3
Chapt. 02
Evolutionary History
• Importance of evolutionary ecology to the
discipline
• Example: Control of penguins in the
Southern Hemisphere vs. their absence in
Northern Hemisphere.
#4
Chapt. 02
Evolutionary History
• Example: Control of penguins in the
Southern Hemisphere vs. their absence in
Northern Hemisphere. (cont.)
– Penguins evolved in the Southern Hemisphere.
#5
Chapt. 02
Evolutionary History
• Example: Control of penguins(cont.).
– Unable to migrate to Northern Hemisphere
#6
Chapt. 02
Evolutionary History
• South America, Africa, and Australia
– Similar climates (Tropical to temperate)
#7
Chapt. 02
#8
Evolutionary History
– Characterized by different inhabitants.
• South America: Ex. Sloths, anteaters, armadillos,
and monkeys with prehensile tails.
– Africa: Ex. Antelopes, zebras, giraffes, lions, baboons,
okapi, and aardvark.
Chapt. 02
#9
Evolutionary History
– Characterized by different inhabitants (cont.).
– Australia: Ex. No native placental mammals except bats,
variety of marsupials, egg-laying montremes, duck-billed
platypus, and the echidna.
• Best explanation of differences: Evolution.
Chapt. 02
Genetic Mutation
• Increase in number of species is primarily
due to mutation.
• Two types of mutation
– Gene or point mutation
– Chromosome mutation
#10
Chapt. 02
Genetic Mutation
• Point mutation
– Results from a misprint in DNA copying
– Example (Figure 2.1)
#11
Chapt. 02
#12
Direction of transcription
DNA AGA
TGA
CGG
RNA UCU ACU GCC
Protein Ser
Thr
Ala
TTT
GCA
AAA CGU
Lys
Arg
Frameshift: Insert T
Transition A-G
DNA GGA TGA
CGG
TTT
GCA
DNA AGT
ATG
ACG
RNA CCU
GCC AAA
CGU
RNA UCA
UAC
UGC CAA ACG
Protein Ser
Tyr
Protein Pro
ACU
Thr
Ala
Lys
Arg
Cys
GTT TGC
Glu
Thr
A..
?
Chapt. 02
Genetic Mutation
• Point mutation (cont.).
– Most changes are caused by frameshift
mutations
– An addition or deletion in the amino-acid
sequence usually leads to drastic and often
fatal mutations
#13
Chapt. 02
Genetic Mutation
• Chromosome mutation
– Four types: deletion, duplications, inversions,
and translocation
– Order of genes is affected
(Figure 2.2).
#14
Chapt. 02
#15
Original
Breakage
A B C D E FG H
Altered
A BC D E F G H
Deletion
A B C D E F H
Eliminated
A B C D E F
Duplication
From another
chromosome
F
Inversion
G
A B
A B C D E FG H
GH
A B C D E F G G H
G
E
A B G F E DC H
D
C
H
A B C D E
FGH
A B C D E T U V
O P Q R S
TUV
O P Q R S F G H
Translocation
O P Q R S T U V
Chapt. 02
Genetic Mutation
• Chromosome mutation (cont.).
– Deletion
• Simple loss of part of a chromosome
• Most common source of new genes
• Often lethal
#16
Chapt. 02
Genetic Mutation
• Chromosome mutation (cont.).
– Duplication
• Arises from chromosomes not being perfectly
aligned during crossing over.
• Results in one chromosome being deficient and the
other one with duplication of genes.
#17
Chapt. 02
Genetic Mutation
– Duplication (cont.).
• May have advantages due to increased enzyme
production.
– Inversion
• Occurs when a chromosome breaks in two places.
When the segment between the two breaks refuses,
it does so in reverse order.
#18
Chapt. 02
Genetic Mutation
– Inversion (cont.).
• Occurs during prophase.
#19
Chapt. 02
Measuring Genetic Variability
• Genetic diversity is essential to the
breeding success of most populations.
• Two individuals with the same form of
enzyme are genetically identical at that
locus.
#20
Chapt. 02
Measuring Genetic Variability
• Variations in gene loci are found through
searching for variations in the enzymes
(allozymes).
• Gel electrophoresis: Technique for
determining differences in allozymes.
#21
Chapt. 02
Measuring Genetic Variability
• Example of Gel electrophoresis: Figure
2.3.
#22
Chapt. 02
Gene Sequencing
• Another method for assessing variations is
the sequence of DNA.
• Made possible through the polymerase
chain reaction (PCR) technique.
#23
Chapt. 02
Gene Sequencing
• Made possible through the polymerase
(cont.).
– Makes millions of copies of a particular region
of DNA, thereby amplifying even minute
amounts of DNA.
#24
Chapt. 02
Gene Sequencing
• Made possible through the polymerase
(cont.).
• Important uses in conservation biology, and rare
and endangered species.
#25
Chapt. 02
Gene Sequencing
• Accelerated through human-made
radiation, UV light, or other mutagens.
#26
Chapt. 02
Mutations
• Rate of occurrence: one per gene locus in
every 100,000 sex cells.
• Only one out of 1,000 mutations may be
beneficial.
#27
Chapt. 02
Mutations
• Estimated that only 500 mutations would
be expected to transform one species into
another.
• Rate of mutation is not the chief factor
limiting the supply of variability.
#28
Chapt. 02
Mutations
• Variability is mainly limited by gene
recombination and the structural patterns
of chromosomes.
#29
Chapt. 02
Genetic Diversity and Population Size
• Function of population size
• Four factors: inbreeding, genetic drift, and
neighborhoods.
#30
Chapt. 02
Inbreeding Depression
• Mating among close relatives.
• Reduced survivorship (Figure 2.4).
#31
Chapt. 02
#32
Percent
60
50
Non-productive
matings
40
Mortality from
birth to four
weeks
30
20
10
0
1
2
3
Years
4
5
6
Chapt. 02
Inbreeding Depression
• Various types of inbreeding (Figure 2.5)
#33
Chapt. 02
#34
Fraction of initial genetic variation
1.0
0.8
C
0.6
B
0.4
A
0.2
0
5
10
Generations
15
20
Chapt. 02
Inbreeding Depression
• Effects of inbreeding on juvenile mortality
(fig. 2.6)
#35
% Juvenile mortality- outbred
Chapt. 02
#36
70
Primates
60
Small Animals
50
40
Saddle back tamarin
Ungulates
Macaque
Chimpanzee
Lemur
30
Giraffe
20
10
0
Rat
20
40
Eld’s deer
Indian elephant
Spider monkey
Oryx
Mandrill
Mouse
100
80
60
% Juvenile mortality-inbred
Chapt. 02
Inbreeding Depression
• Effects of inbreeding on small populations
(Figure 2.7).
#37
Chapt. 02
Inbreeding Depression
• Example of inbreeding: Greater Prairie
Chicken (Figures 2.8 and 2.9).
#38
Eggs hatched
#39
100
75
150
Prairie chicken cocks
100
50
50
25
10
0
1973
1980
Year
1990
Eggs hatched (%)
Number of prairie chicken cocks
Chapt.
200 02
Chapt. 02
Inbreeding Depression
• Example of inbreeding and relation to
extinction: Glanville fritillary butterfly
(Figure 2.10)
#40
1.0
Chapt. 02
#41
N=1000
Fraction of initial genetic variation
0.9
0.8
N=300
0.7
0.6
N=100
0.5
N=20
0.4
0.3
0.2
0.1
0
100
200
300
Generations
400
500
Chapt. 02
Genetic Drift
• Probability of the failure to mate
– Loss of possible rare gene
– Loss of genetic information for subsequent
generations resulting in a loss of genetic
diversity.
#42
Chapt. 02
Genetic Drift
• Probability of the failure to mate
– Small populations more susceptible to drift.
– The rate of loss of original diversity over time
is approximately
#43
Chapt. 02
Genetic Drift
• Probability of the failure to mate
– equal to 1/2N per generation.
– Example:
• 1. N = 500 then 1/2N = 0.001 or 0.1% genetic
diversity lost per generation.
#44
Chapt. 02
Genetic Drift
• Probability of the failure to mate
– equal to 1/2N per generation.
– Example:
• N = 50 then 1/2N = 0.01 or 1% genetic diversity
lost per generation.
#45
Chapt. 02
Genetic Drift
• Probability of the failure to mate
– Example: (cont.).
• Over 20 generations, the population of 500 will
still retain 98% of the original variation, but the
population of 50 will only retain 81.79%.
#46
Chapt. 02
Genetic Drift
• Probability of the failure to mate
– Example: (cont.).
• 50/500 Rule: Need 50 individuals to prevent
excess inbreeding and 500 is the critical size to
prevent genetic drift.
#47
Chapt. 02
Genetic Drift
– Effects of immigration on genetic drift (Figures
2.11 and 2.12). Often immigration of only one
or two individuals into a population can
counteract genetic drift
#48
Percentage of initial
genetic variation remaining
Chapt. 02
#49
Number of
immigrants per
generation
100
5
2
1
90
80
0.5
70
0.1
60
None
50
10
20
30
40
50
Generation
60
70
80
90
100
Percentage of populations persisting
Chapt.
02
100
#50
N = 101 or more
80
N = 51-100
N =16-30
60
N = 31-50
40
N = 15 or less
20
0
10
20
30
Time (years)
40
50
Chapt. 02
#51
Neighborhoods and Effective Population
Size
• Effective population size is determined on
mating range.
• Individuals may only mate within their
neighborhood.
Chapt. 02
#52
Neighborhoods and Effective Population
Size
• Example: Deer mice. 70% of the males
and 85% of the females breed within 150m
of their birthplaces.
Chapt. 02
#53
Neighborhoods and Effective Population
Size
• Harem Effects (cont.).
– Even within a neighborhood, some individuals
may not reproduce.
– In a harem structure, only a few dominant
males breed.
Chapt. 02
#54
Neighborhoods and Effective Population
Size
• Harem Effects (cont.).
– Effective Population Size
• NE = (4 Nm Nf) / (Nm + Nf).
• Where: NE = Effective Population Size; Nm =
Number of Breeding Males; Nf = Number of
Breeding Females.
Chapt. 02
#55
Neighborhoods and Effective Population
Size
• Harem Effects(cont.).
– Example of Effective Breeding Size (Figure
2.13).
Chapt. 02
Applied Ecology: Can Cloning Help Save
Endangered Species?
• Harem Effects
– Dolly, the cloned sheep – Ian Williams 1997
(Photo 1).
#56
Chapt. 02
Applied Ecology: Can Cloning Help Save
Endangered Species?
• Harem Effects (cont.).
– Can this technique be used to save endangered
species?.
• Need knowledge of reproductive cycle.
#57
Chapt. 02
Applied Ecology: Can Cloning Help Save
Endangered Species?
• Harem Effects (cont.).
– Can this technique be used to save endangered
species?.
• Need for surrogate females.
• Expense associated with cloning.
• Can not address genetic diversity.
#58
Chapt. 02
Summary
• New species arise from the accumulation
of gene and chromosome mutations.
#59
Chapt. 02
Summary
• Genetic variation is reduced in populations
due to inbreeding, genetic drift, and
neighborhoods. 50/500 Rule.
#60
Chapt. 02
Summary
• Humans can more individuals of wild
populations, which could counteract
genetic drift.
• Effective population size can be reduced
by harem mating structures or territoriality.
#61
Chapt. 02
#62
Phenotype表現型: 一個生物體可觀測的性狀。
Genotype基因型： 特定組織中相關的一個或幾個基
因組成。
Chapt. 02
#63
Gene基因： 遺傳的基本單位。
Gene pool基因庫： 一個群體的基因總
和。
Population genetics族群（群體）遺傳學
： 在群體的水平上對基因頻率、基因型
、表現型和交配系統的研究。
Chapt. 02
#64
Allele等位基因：位於同源染色體的同一
位點上的一對基因中的一個，或一個基因
的多種形式中的一個，又稱為
allelomorph.
Locus座位： 一個基因在一條染色體上的
固定位置。
Chapt. 02
The mechanism of evolution:
1. Genetic drift遺傳漂變
2. Gene flow基因流動
3. Mutation突變
4. Nonrandom mating非隨機配對
5. Natural selection自然選擇
#65
Chapt. 02
#66
1. Genetic drift遺傳漂變:
在一個小群體內，基因頻率從一個世
代到下一個世代的隨機變動。
. Bottleneck effect（瓶頸效應）
. Founder effect （創造者效應）
Chapt. 02
#67
2. Gene flow基因流動:
通過雜交(hybridization)或回交(back
cross)，將一個群體的遺傳特性傳遞給另
一個群體基因組。
Backcross回交：
一種F1雜合體與一種P1基因型個體間的
雜交。
Chapt. 02
#68
3. Mutation突變：
突變比例通常每十萬到一百萬個配子之中
只有一個基因座突變的機率。
Random changes： 隨機變異。
Chapt. 02
4. Nonrandom mating非隨機配對：
個子高矮，膚色，財富
#69
Chapt. 02
#70
5. Natural selection自然選擇：
只有那些具有有利變異的後代可以在生
存競爭中生存下來，通過以後各代有利變
異得到累積，使這樣的後代漸漸與其親代
不同。
Chapt. 02
5. Natural selection自然選擇：
(1). Stabilizing selection穩定選擇：
(2). Direction selection定向選擇:
(3). Disruptive selection分裂選擇:
#71
Chapt. 02
#72
(1). Stabilizing selection穩定選擇：
環境條件有利於族群的表現型性狀常態
分布線的平均值附近時，對於兩側的極端
個體有較高的淘汰率。例如人的出生死亡
率和出生重的關係。
Chapt. 02
#73
(2). Direction selection定向選擇:
選擇對於一側極端的個體有利，從而使族
群的平均值向這一側移動。例如大部分的
人工選擇。
Chapt. 02
#74
(3). Disruptive selection分裂選擇:
選擇對兩側極端的個體有利，而不利於
中間的個體，從而使族群分成兩個部份。
Chapt. 02
#75
自然選擇的條件：
1. 任何生物單位具有複製自身（繁殖）的
能力。
2. 子代的數目超過其替代的需要。
3. 子代的存活決定於某些特徵（外表型或
是基因型）。
4. 這些特徵具有遺傳傳遞的機制。
Chapt. 02
#76
Soft selection:
特定基因型的個體比族群內的其他個體，
具有更強取得資源的競爭力，因此可以有
較高的活存機率。
Chapt. 02
#77
Hard selection:
一個個體的適應度（Fitness:存活率、死
亡率等量化差異）和其他基因型無關，一
種突發的外界環境因素可能導致高死亡率
的發生。
Chapt. 02
#78
Gamete selection配子選擇：
選擇對基因頻率的影響，可以發生在配子
上，例如精子的活動力差異可以受物理的
或化學的狀況所影響。
Chapt. 02
#79
Kin selection親屬選擇：
相關個體間（親屬間）利他行為所產生的
總適應度提高的一種選擇。例如土撥鼠發
出警告叫聲的土撥鼠可以使其他親屬有較
高的活存率，但是本身較易受攻擊而死亡
。
Chapt. 02
#80
Sexual selection性別選擇：
最強壯或最活躍的個體具有較高的交配機
率，因此這種個體的特徵在後代中會不斷
的強化發展。例如孔雀的尾羽、鬥魚的鰭
、雄鹿的角。
Chapt. 02
#81
Frequency-dependent selection頻度相
關的選擇：
自然選擇作用在出現頻度最多的外表型個
體上較高，其結果將造成其生殖程度下降
，如此可以使一個群維持平衡式的多形態
性。如果選擇對於某種頻度的個體最有利
，則將提高這種有個體的適應度。
Chapt. 02
#82
The evolution of interactions among
species
Mimicry擬態：
Coevolution共同演化
Parasitism寄生:
Mutualism互利共生：
Competition競爭：
Predator-prey掠食者與獵物：
Herbivore-plant草食性動物與植物：
Chapt. 02
#83
Mimicry擬態：從模仿其他物種的外表上
獲得好處的現象。
.Bastesian mimicry貝氏擬態：無毒害的物種藉由模
擬有害物種而獲利的情形。
.Mullerian mimicry木氏擬態: 兩種不同物種之間的
擬態。
.Aggressive mimicry攻擊性擬態： 有毒的種類模擬
無讀得種類，以提升其偽裝效果，增加掠食成功率
。
Chapt. 02
Coevolution共同演化：
例如植物和昆蟲間的共同演化。
#84
Chapt. 02
Discussion Question #1
• Small population size is detrimental to genetic
variability. Why is habitat fragmentation
detrimental to populations, and can linking
conservation areas by corridors or sitting them
close together help alleviate this problem?
#85
Chapt. 02
Discussion Question #2
• We can have inbreeding depression as well as
outbreeding depression (where local populations
are highly adapted to their local environment, and
outbreeding reduces fitness). By what mechanisms
do you think this works and what implications does
it have for conservation biology?
#86
Chapt. 02
Discussion Question #3
• In 1986 the California condor had declined to
only 27 individuals. Since then over 150
condors have been bred and 88 released back
into the wild. What genetic problems do you
think might be encountered in trying to reestablish this population in nature?
#87