LESSON 2: DIVERGENCE AND DIVERSITY

The diversity of life is astounding. On our planet we can encounter literally millions of different types of organisms, from single-celled prokaryotes and protists, to multicellular plants, fungi, and animals. How do we begin, then, to account for this diversity? In last week’s lessons, we learned about some of the processes that have apparently led to this diversity of life – natural selection, mutation, genetic drift, gene flow, and sexual selection. In this week’s material, you will learn how biologists use the general concepts of evolution and common descent to classify the diversity of life. Along the way, you will revisit the importance of mutations in DNA, in particular a type of mutation called a duplication, and gain an understanding of the resulting differences in the DNA of organisms are used by scientists to investigate the history of life.

Learning Objectives

• Try to comprehend the astounding diversity of life.
• Understand the link between evolutionary history and classification.
• Understand how different types of data (morphological, genetic, geographical distribution, fossil record, etc.) are used in determining the relationships among organisms.
• Understand the principle of parsimony.
• Know what a phylogenetic tree is, and how it ‘works’.
• Become familiar with the Linnaean system of classification, including its hierarchical nature and the concept of binomial nomenclature.

Topics covered in this Lesson

• Genetic Variation
• Genetic Divergence
• Classification of Bio Diversity

Metronome of Genetic Variation

Evolutionary changes involve a complex interplay among many factors.  On one hand natural selection continually filters characteristics, reinforcing advantageous genes and removing deleterious ones. On the other hand, mutation and sexual reproduction (not to mention conjugation, transformation, and transduction) are always producing new genetic characteristics that will be put to the test by natural selection. Throw in some phenotypic plasticity and the possibilities get interesting.

Learning Objectives

• Know how genetic variability is maintained in a species.

• Understand that the expression of many genes is influenced by an organism's environment.

• Know that gene duplication appears to have played a major role in increasing genome size.

• Know what homologous genes are.

Measuring Genetic Divergence

Recently the tools for studying evolution got smaller and much more powerful.  Molecular genomics is changing the way we look at evolution, speciation, human disease, and just about everything else.  Suddenly neutral mutations, the ones that natural selection ignores, are becoming important in our understanding of how different species are related.  Molecular sequencing has opened up a vast new chapter in biology.

Learning Objectives

• Understand the importance of neutral mutations in studying molecular sequences.

• Know the difference between synonymous and nonsynonymous mutations.

• How do we calculate the degree of divergence between two molecular sequences?

• Know what types of molecules are useful for different types of studies.

Classification of Bio Diversity

Classification systems are never perfect, but they serve some important purposes. With the enormous diversity in the biological world, we need some logical way to keep track of all the organisms and to be able to communicate with other scientists about them. As our knowledge of organisms and how they are related continues to grow, our ideas about the best way to categorize them changes.

Biological diversity is fascinating…and overwhelming, especially given the fact that we haven’t come close to discovering or describing all of the species of organisms on earth. To impose a classification system on organisms requires a logical set of rules that scientists can agree on and use consistently. In this module we will look at how organisms are classified, what types of data are used to do the classification, and what types of information we can glean from the relationships among different organisms.

Learning Objectives

• Why do we bother to classify organisms?
• What are some of the advantages of classification systems?
• What are some of the disadvantages of classification systems?
• Understand the difference between ancestral and derived traits
• Understand the difference between homologous and homoplastic traits
• What types of information are used in constructing phylogenies?
• How are evolutionary relationships illuminated using phylogenies?
• How are molecular data used in conjunction with fossil and morphological data?