Evolution and Origin of Biodiversity: Patterns of Descent with Modification

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1 Evolution and Origin of Biodiversity: Patterns of Descent with Modification by CHED on January 10, 2017 lesson duration of 20 minutes under General Biology 2 generated on January 10, 2017 at 04:19 am Tags: Evolution and Origin of Biodiversity: Patterns of Descent with Modification

2 Generated: Jan 10, :19 PM Evolution and Origin of Biodiversity: Patterns of Descent with Modification ( 1 hour and 20 mins ) Written By: CHED on July 18, 2016 Subjects: General Biology 2 Tags: Evolution and Origin of Biodiversity: Patterns of Descent with Modification Resources n/a n/a Content Standard Relevance, Mechanisms, Evidence/Bases, and Theories of Evolution Performance Standard n/a Learning Competencies Show patterns of descent with modification from common ancestors to produce the organismal diversity observed today Introduction 5 mins Quick Review 1. Give a quick review of the different mechanisms that bring about changes in the population and ultimately lead to evolution. Teacher Tip: Let your learners recall the mechanisms that cause changes in gene frequencies. Motivation 15 mins 1 / 6

3 Classifying Animals 1. Ask your learners to give an organism which can be an animal or a plant species. 2. Ask them further if they had seen different kinds or variants of this species and also other species which look like them because they are related. An example is the cat family where lion, tiger, cheetah, etc. belong. 3. Then tell them that the lesson is about how different kinds of organisms or species are produced over time. Instruction 15 mins Species 1. Define 1. Define species species according according to the to biological the biological species species concept. concept. Ernst Ernst Mayer s Mayer s definition: definition: Species Species are are groups groups of of interbreeding natural populations that are reproductively isolated from other such groups. 2. Discuss the reproductive isolating mechanisms A. Pre-zygotic isolation mechanisms prevent fertilization and zygote formation. I. geographic or ecological or habitat isolation potential mates occupy different areas or habitats thus, they never come in contact II. temporal or seasonal isolation different groups may not be reproductively mature at the same season, or month or year III. behavioral isolation patterns of courtship are different IV. mechanical isolation differences in reproductive organs prevent successful interbreeding V. gametic isolation incompatibilities between egg and sperm prevent fertilization Teacher Tip: 1. Take note that there are different species concepts but the best used and most popular among biologists is the biological species concept All All reference books in in General Biology gives examples of of the the occurrence of of the the isolating mechanisms in in different different organisms and and also also specific specific examples of the of the three three models models of of speciation. To To make make things things more more interesting interesting it will it help will to help show to show photographs photographs of the of species the species to your to learners. your learners. You may You download may download the the photographs or illustrations from the internet using google images. 3. Give 3. Give examples examples of of organisms instances or instances for each for each reproductive isolating isolating mechanism. Think Think of local of local examples. B. Post-zygotic isolation mechanisms allow fertilization but nonviable or weak or sterile hybrids are formed. I. hybrid inviability fertilized egg fails to develop past the early embryonic stages II. hybrid sterility hybrids are sterile because gonads develop abnormally or there is abnormal segregation of chromosomes during meiosis 2 / 6

4 III. hybrid breakdown - F1 hybrids are normal, vigorous and viable, but F2 contains many weak or sterile individuals 3. Let your learners recall the different genetic mechanisms that can change gene frequencies. Discuss with them that in the presence of a reproductive isolating mechanism, genetic drift, natural selection, mutation and gene flow are free to operate on the population. These will lead to genetic divergence and ultimately to species formation or speciation. 4. Discuss the modes of speciation: A. Allopatric speciation or geographic speciation (allo other, patric place; other place ) - - occurs when some members of of a a population become geographically separated from from the the other members thereby preventing gene flow. flow. Examples of geographic barriers are bodies of water and mountain ranges. B. Sympatric speciation (sym same, patric place; same place ) - - occurs when members of of a a population that that initially occupy the the same habitat within the the same range diverge into into two two or or more different species. It It involves abrupt genetic genetic changes changes that that quickly quickly lead lead to the to the reproductive isolation isolation of a of group a group of individuals. of individuals. Example Example is change is change in in chromosome number (polyploidization). C. Parapatric speciation (para beside, patric place; beside each other ) occurs when the groups that evolved to be separate species are geographic neighbors. Gene flow occurs but with great distances is reduced. There is also abrupt change in the environment over a geographic border and strong disruptive selection must also happen. 5. You may show the following diagram to differentiate the three models of speciation You You can can wrap wrap up up your your lecture by by mentioning that that present-day species evolved from from earlier earlier species and and that that the the relatedness of of organisms is is the result of of common ancestry. This can be be supported by by morphological and anatomical data, homology, biogeography, DNA and protein sequences (molecular data), and embryology. All these evidences of evolution (descent with modification) will be discussed in a separate topic. Practice 20 mins Activity Based on the descriptions let your learners identify the given isolating mechanisms: 1. Two species of garter snakes live in the same region but one lives in water and the other on land 3 / 6

5 2. Two species of meadowlarks with different mating songs 3. Two species of trout that breed in different seasons 4. Mule is the sterile offspring of a horse and a donkey 5. Two species of plants flower at different months Based on the descriptions let your learners identify the mode of speciation: The The hemp nettle, Galeopsis tetrahit is is a a tetraploid found to to thrive in in the the same area area as as two two other diploids species, Galeopsis pubescens and Galeopsis speciosa The Panama porkfish, Anisotremus taeniatus, found in in the Pacific Ocean is is morphologically similar to to the porkfish, Anisotremus virginiacus, found found in the in the Caribbean Sea Sea are are separated separated by a by land a land bridge bridge between between North North and and South South America called the Isthmus of Panama The The Siberian lesser black-backed gull, gull, lesser black-backed gull gull and and herring gull gull are are all all found in in the the Arctic region. The lesser black-backed gull interbreeds with the Siberian lesser black-backed gull but not with the herring gull. Enrichment 20 mins Film Viewing 1. Show a short film (~15 minutes) about the The Beak of the Finch made by the Howard Hughes Medical Institute. The film can be streamed from the HHMI Biointeractive website ( beak-finch) or through YouTube ( watch?v=mcm23m-ccog). Evaluation 5 mins You may give a quiz about this topic. Here are some sample questions. 1. Which of the following statements about biological species is(are) correct? I. Biological species is a group of individuals whose members interbreed with one another. II. Biological species are the model used for grouping extinct forms of life. III. Members of biological species produce viable, fertile offsprings. A. I only B. II only C. I and III D. II and III E. I, II, and III Answer Key: 4 / 6

6 1. C 2. B 3. B 4. A 5. C 2. The following isolating mechanisms prevent fertilization and formation of zygote except A. Temporal isolation B. Hybrid breakdown C. Gametic isolation D. Ecological isolation E. Behavioral isolation For numbers 3-5, use the following choices: A. Allopatric speciation B. Sympatric speciation C. Parapatric speciation 3. Occurrence of abrupt genetic change cause reproductive isolation between groups of individuals. 4. Occurs when populations are separated by a geographic barrier. 5. Abrupt 5. Abrupt change change in the in the environment over over a a geographic border border and and strong strong disruptive selection selection affects affects gene gene flow flow between neighboring populations. 5 / 6

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