Chapter 2 Genetics and Ecology © 2002 by Prentice Hall, Inc. Upper Saddle River, NJ 07458

Chapter 2Genetics and Ecology

© 2002 by Prentice Hall, Inc.

Upper Saddle River, NJ 07458

#2Chapt. 02

Outline

• Species occurrence due to evolutionary past.

• Mutations and chromosomal rearrangements result in a wide variety of species on earth.

#3Chapt. 02

Outline

• Genetic variability can be measured by allozymes or DNA sequencing.

• Mechanisms for reductions in genetic variability in populations.

#4Chapt. 02

Evolutionary History

• Importance of evolutionary ecology to the discipline

• Example: Control of penguins in the Southern Hemisphere vs. their absence in Northern Hemisphere.

#5Chapt. 02

Evolutionary History

• Example: Control of penguins in the Southern Hemisphere vs. their absence in Northern Hemisphere. (cont.)– Penguins evolved in the Southern Hemisphere.

#6Chapt. 02

Evolutionary History

• Example: Control of penguins(cont.). – Unable to migrate to Northern Hemisphere

#7Chapt. 02

Evolutionary History

• South America, Africa, and Australia– Similar climates (Tropical to temperate)

#8Chapt. 02

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.

#9Chapt. 02

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.

#10Chapt. 02

Genetic Mutation

• Increase in number of species is primarily due to mutation.

• Two types of mutation– Gene or point mutation– Chromosome mutation

#11Chapt. 02

Genetic Mutation

• Point mutation– Results from a misprint in DNA copying – Example (Figure 2.1)

#12Chapt. 02

Direction of transcription

DNA AGA TGA CGG TTT GCA

RNA UCU ACU GCC AAA CGU

Protein Ser AlaThr Lys Arg

Transition A-G

DNA GGA TGA CGG TTT GCA

RNA CCU GCC AAAACU CGU

Protein Pro Thr Ala Lys Arg

Frameshift: Insert T

DNA

RNA

Protein

AGT

UCA

ATG ACG GTT TGC A..

UAC UGC CAA ACG

Ser Tyr Cys Glu Thr ?

#13Chapt. 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

#14Chapt. 02

Genetic Mutation

• Chromosome mutation– Four types: deletion, duplications, inversions,

and translocation– Order of genes is affected (Figure 2.2).

#15Chapt. 02

Original

A B C D E F G HBreakage

G HA B C D E F A B C D E F H

Altered

A B C D E F G H

From another chromosome

A B C D E F G G H

A B G F E D C H

G

FE

D

C

H

Deletion

Duplication

Inversion

Translocation

A B C D E T U VA B C D E F G HA B C D E F G H

O P Q R S T U V O P Q R S T U V O P Q R S F G H

A B

G

Eliminated

#16Chapt. 02

Genetic Mutation

• Chromosome mutation (cont.).– Deletion

• Simple loss of part of a chromosome• Most common source of new genes• Often lethal

#17Chapt. 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.

#18Chapt. 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.

#19Chapt. 02

Genetic Mutation– Inversion (cont.).

• Occurs during prophase.

#20Chapt. 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.

#21Chapt. 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.

#22Chapt. 02

Measuring Genetic Variability

• Example of Gel electrophoresis: Figure 2.3.

#23Chapt. 02

Gene Sequencing

• Another method for assessing variations is the sequence of DNA.

• Made possible through the polymerase chain reaction (PCR) technique.

#24Chapt. 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.

#25Chapt. 02

Gene Sequencing

• Made possible through the polymerase (cont.).

• Important uses in conservation biology, and rare and endangered species.

#26Chapt. 02

Gene Sequencing

• Accelerated through human-made radiation, UV light, or other mutagens.

#27Chapt. 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.

#28Chapt. 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.

#29Chapt. 02

Mutations

• Variability is mainly limited by gene recombination and the structural patterns of chromosomes.

#30Chapt. 02

Genetic Diversity and Population Size

• Function of population size• Four factors: inbreeding, genetic drift, and

neighborhoods.

#31Chapt. 02

Inbreeding Depression

• Mating among close relatives.• Reduced survivorship (Figure 2.4).

#32Chapt. 02

Non-productivematings

60

50

40

30

10

20

0

Perc

ent

1 2 3 4 5 6

Mortality from birth to four weeks

Years

#33Chapt. 02

Inbreeding Depression

• Various types of inbreeding (Figure 2.5)

#34Chapt. 02

0 5 10 15 20

A

B

C

0.2

0.4

0.6

0.8

1.0

Generations

Fract

ion o

f in

itia

l geneti

c vari

ati

on

#35Chapt. 02

Inbreeding Depression

• Effects of inbreeding on juvenile mortality (fig. 2.6)

#36Chapt. 02

Saddle back tamarinUngulates

Primates

Small Animals

% Juvenile

mort

alit

y-

outb

red

70

60

50

40

30

20

10

0

Chimpanzee

Macaque

Lemur

Eld’s deer

Oryx

MouseMandrill

Indian elephant

Giraffe

10080604020

% Juvenile mortality-inbred

Spider monkeyRat

#37Chapt. 02

Inbreeding Depression

• Effects of inbreeding on small populations (Figure 2.7).

#38Chapt. 02

Inbreeding Depression

• Example of inbreeding: Greater Prairie Chicken (Figures 2.8 and 2.9).

#39Chapt. 02

10

50

100

150

200 Eggs hatched

0

25

50

75

100

Prairie chicken cocks

Num

ber

of

pra

irie

chic

ken c

ock

s

1973 1980 1990

Year

Eggs

hatc

hed (

%)

#40Chapt. 02

Inbreeding Depression

• Example of inbreeding and relation to extinction: Glanville fritillary butterfly (Figure 2.10)

#41Chapt. 02

Fract

ion o

f in

itia

l geneti

c vari

ati

on

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

N=20

N=100

N=300

N=1000

0 100 200 300 400 500

Generations

#42Chapt. 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.

#43Chapt. 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

#44Chapt. 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.

#45Chapt. 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.

#46Chapt. 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%.

#47Chapt. 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.

#48Chapt. 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

#49Chapt. 02

Number of immigrants pergeneration

5

21

0.5

0.1

None

10 20 30 40 50 60 70 80 90 100

Generation

Perc

enta

ge o

f in

itia

l g

eneti

c vari

ati

on r

em

ain

ing

50

60

70

80

90

100

#50Chapt. 02

Perc

enta

ge o

f popula

tions

pers

isti

ng

0

20

40

60

80

100

10 20 30 40 50

Time (years)

N = 101 or more

N = 51-100

N = 31-50

N = 15 or less

N =16-30

#51Chapt. 02

Neighborhoods and Effective Population Size

• Effective population size is determined on mating range.

• Individuals may only mate within their neighborhood.

#52Chapt. 02

Neighborhoods and Effective Population Size

• Example: Deer mice. 70% of the males and 85% of the females breed within 150m of their birthplaces.

#53Chapt. 02

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.

#54Chapt. 02

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.

#55Chapt. 02

Neighborhoods and Effective Population Size

• Harem Effects(cont.).– Example of Effective Breeding Size (Figure

2.13).

#56Chapt. 02

Applied Ecology: Can Cloning Help Save Endangered Species?

• Harem Effects– Dolly, the cloned sheep – Ian Williams 1997

(Photo 1).

#57Chapt. 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.

#58Chapt. 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.

#59Chapt. 02

Summary

• New species arise from the accumulation of gene and chromosome mutations.

#60Chapt. 02

Summary

• Genetic variation is reduced in populations due to inbreeding, genetic drift, and neighborhoods. 50/500 Rule.

#61Chapt. 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.

#62Chapt. 02

 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。

#63Chapt. 02

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。

#64Chapt. 02

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。

#65Chapt. 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

#66Chapt. 02

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）

#67Chapt. 02

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。

#68Chapt. 02

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。

#69Chapt. 02

4. Nonrandom mating 非隨機配對：

個子高矮，膚色，財富

#70Chapt. 02

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。

#71Chapt. 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 :

#72Chapt. 02

(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。

#73Chapt. 02

(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。

#74Chapt. 02

(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。

#75Chapt. 02

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。

#76Chapt. 02

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。

#77Chapt. 02

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。

#78Chapt. 02

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。

#79Chapt. 02

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。

#80Chapt. 02

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。

#81Chapt. 02

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。

#82Chapt. 02

The evolution of interactions among speciesMimicry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：

#83Chapt. 02

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。

#84Chapt. 02

Coevolution共同演化：

例如植物和昆蟲間的共同演化。

#85Chapt. 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?

#86Chapt. 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?

#87Chapt. 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 re-establish this population in nature?