Microevolution 微演化 生物及解剖學科呂美華.

Transcription

1 Microevolution 微演化 生物及解剖學科呂美華

2 Overview: The smallest unit of evolution A. The population evolved, not its individual members The average beak size in the seed-eating bird B. Microevolution 微演化 Allele frequency change 對偶基因頻率 Mechanisms Medium ground finch (Geospiza fortis) 勇地雀 Evidence of selection by food source

3 23.1 Genetic variation makes evolution possible A. Genetic variation 遺傳變異 Discrete characters 明確性狀 Either-or basis Determined by a single gene locus Quantitative characters 數量性狀 Vary along a continuum within a population Polygenic inheritance 多基因遺傳 Phenotypic variation of coat color in horses

4 Nonheritable variation 非遺傳變異 : these caterpillars owe their different appearances to chemicals in their diets, not to their genotypes

5 B. Sources of genetic variation Formation of new alleles: mutation Point mutation 點突變 - Harmful, beneficial, or neutral

6 Altering gene number or position Deletion 缺失 Duplication 重複 : olfactory receptor genes 嗅覺接受器基因 Inversion 倒位 Translocation 易位 Rapid reproduction Mutation rates: low in animals and plants, lower in prokaryotes Short generation time: prokaryotes and viruses

7 Sexual reproduction 有性生殖 Crossing over 互換 Independent assortment of chromosomes 獨立分配 Fertilization 受精

8 23.2 The Hardy-Weinberg equation can be used to test whether a population is evolving One species, two populations (caribou 北美馴鹿 )

9 A. Gene pools and allele frequencies 基因庫及對偶基因頻率 表現型 基因型 Incomplete dominance 不完全顯性 Homozygous Heterozygous 同基因型組合異基因型組合 p+q=1

10 B. The Hardy-Weinberg equation 哈溫方程式 Hardy-Weinberg equilibrium 哈溫平衡 Selecting alleles at random from a gene pool

11 p 2 + 2pq + q 2 = 1

12 Conditions for Hardy-Weinberg equilibrium

13 Applying the Hardy-Weinberg equation Phenylketonuria (PKU) 苯丙酮尿症 *Homozygosity for a recessive allele 同型接合性, 隱性對偶基因 1/10,000 babies q2 = q = 0.01 p = 1 - q = = 0.99 The frequency of carriers: 2pq = 2 x 0.99 x 0.01 = (approximately 2%) 苯丙胺酸

14 23.3 Natural selection, genetic drift, and gene flow can alter allele frequencies in a population A. Natural selection Selective force of DDT in fruit fly population B. Genetic drift 遺傳漂變 : caused by chance events

15 The founder effect 奠基者效應 A recessive allele for retinitis pigmentosa 視網膜色素病變 Resident of Tristan da Cunha in the early 1900s

16 The bottleneck effect 瓶頸效應

17 Case study: impact of genetic drift on the greater prairie chicken Loss of genetic variation Increase in the frequency of harmful alleles Effects of genetic drift: A summary Genetic drift is significant in small populations Genetic drift can cause allele frequencies to change at random Genetic drift can lead to a loss of genetic variation within populations Genetic drift can cause harmful alleles to become fixed 大草原榛雞

18 C. Gene flow 基因流動 Reduce differences between populations over time

19 Local adaptation 區域適應 Variation in banding pattern in Lake Erie water snakes Increase the fitness of a population: mosquito (insecticide-resistance alleles) The flow of insecticide resistance alleles into a population can cause an increase in fitness

20 23.4 Natural selection is the only mechanism that consistently causes adaptive evolution A. Three modes of selection Directional selection 方向選擇 Disruptive selection 分歧選擇 Stabilizing selection 穩定選擇

21 B. The key role of natural selection in adaptive evolution Examples of the adaptations of organisms 烏賊 Moveable jaw bones in snakes

22 C. Sexual selection 性擇 Sexual dimorphism 性別二型性 Secondary sexual characteristics 第二性徵 Sexual dimorphism (peacock at left; peahen at right)

23 Intrasexual selection 同性間性擇 Intersexual selection (mate choice) 異性間性擇, 配偶選擇 A contest for access to mate A male peacock s advertisement for mates A male gray tree frog calling for mates

24 The good genes hypothesis The duration of a male s mating call is indicative of the male s overall genetic quality

25 D. Balancing selection 平衡選擇 Frequency-dependent selection 頻度依賴選擇 Scale-eating fish 吃鱗片的魚 Selection favors whichever phenotype is less common in a population

26 Heterozygote advantage 異型合子優勢 瘧疾 瘧疾 In regions where the malaria parasite is common, selection favors individuals heterozygous for the sickle-cell allele

27 E. Why natural selection cannot fashion perfect organisms Selection can act only on existing variations Evolution is limited by historical constraints 歷史的限制 Adaptations are often compromises Chance, natural selection, and the environment interact Evolutionary compromise