CCE 2: Review
Okay! I don't really know what things are common knowledge and what aren't, so I figure the way to handle it is that I'm just going to start lobbing very general and high-level information. If nobody comments on a topic, I'll assume that we all know about it and feel pretty comfortable with that issue. If there are comments on something, we'll go into it in more detail. That should hopefully let us fast-forward to the ideas that are new to people.
Also, numbering seems to be working pretty well for helping us keep track of subjects. But please, don't hesitate if you have any suggestions about the format of our discussion.
The important background ideas you need to understand are:
1) Basic (Mendelian) genetics. Genes are the blueprint for an organism's body. An organism inherits its genes from its parents; in the case of diploid organisms (like most animals), it gets one set of genes from each parent. An organism's genotype is the particular combination of genes that it carries; its phenotype is the way that those genes are expressed. The different possible "flavors" of a gene are called alleles. If one allele is dominant, an organism can carry a recessive allele without expressing it in its phenotype, but still pass on the recessive allele to its children.
2) Molecular genetics. Genes are carried on DNA molecules, which structurally encode the information your body uses to build proteins (and, hence, everything else). DNA is make of four nucleotides (anenine, thymine, guanine, cytosine) that pair up (A-T and C-G) in long strands. The 64 possible nucleotide triplets, or codons, code for twenty amino acids and a "stop" codon that signals the end of the protein. DNA gets "read" by the cellular machinery that translates it into a protein. DNA gets replicated during reproduction and cell division, but not always perfectly.
3) Phylogenetic trees. If everything is descended from a common anscestor, you can organize species into a tree, just like a geneological tree, according to when various species split from one another. This is called a phylogenetic tree. You can also classify organisms (or automobiles, or languages) into a nested hierarchy (which has a tree structure) based on their shared derived characteristics. This is called cladistics, and there are a number of different ways to do the classification.
4) Homology. Different species will have morphological similarities. An analogous similarity is one that can be explained by a common functional requirement: any creature that's going to fly needs wings; any creature that swims fast needs a hydrodynamic shape. A homologous similarity (or homology) is one that is not functionally necessary. For example, there's no pressing need for all tetrapods to have five digits; we'd get along just as well with three, four, six, seven, or probably even twelve sets of finger-bones on each hand/foot/fin.
5) Species. There are a number of different definitions for the term "species"; what the evidence is for evolution being able to produce a new species depends on which definition you're using. The reproductive concept of species is "a set of organisms that interbreed among themselves but do not breed with members of other species". The phenotypic concept defines a species as a group of organisms that are sufficiently similar to one another and sufficiently different from members of other species; this is probably the closest to our intuitive defintion of the term. A useful definition that makes no assumptions about evolution is: "species are groups of actually or potentially interbreeding natural populations that are reproductively isolated from other such groups".
Okay! So now, class, your assignment is: tell me what we need to go into more detail about. Is this all review? All makes sense? What do you want to talk about?
Also, numbering seems to be working pretty well for helping us keep track of subjects. But please, don't hesitate if you have any suggestions about the format of our discussion.
The important background ideas you need to understand are:
1) Basic (Mendelian) genetics. Genes are the blueprint for an organism's body. An organism inherits its genes from its parents; in the case of diploid organisms (like most animals), it gets one set of genes from each parent. An organism's genotype is the particular combination of genes that it carries; its phenotype is the way that those genes are expressed. The different possible "flavors" of a gene are called alleles. If one allele is dominant, an organism can carry a recessive allele without expressing it in its phenotype, but still pass on the recessive allele to its children.
2) Molecular genetics. Genes are carried on DNA molecules, which structurally encode the information your body uses to build proteins (and, hence, everything else). DNA is make of four nucleotides (anenine, thymine, guanine, cytosine) that pair up (A-T and C-G) in long strands. The 64 possible nucleotide triplets, or codons, code for twenty amino acids and a "stop" codon that signals the end of the protein. DNA gets "read" by the cellular machinery that translates it into a protein. DNA gets replicated during reproduction and cell division, but not always perfectly.
3) Phylogenetic trees. If everything is descended from a common anscestor, you can organize species into a tree, just like a geneological tree, according to when various species split from one another. This is called a phylogenetic tree. You can also classify organisms (or automobiles, or languages) into a nested hierarchy (which has a tree structure) based on their shared derived characteristics. This is called cladistics, and there are a number of different ways to do the classification.
4) Homology. Different species will have morphological similarities. An analogous similarity is one that can be explained by a common functional requirement: any creature that's going to fly needs wings; any creature that swims fast needs a hydrodynamic shape. A homologous similarity (or homology) is one that is not functionally necessary. For example, there's no pressing need for all tetrapods to have five digits; we'd get along just as well with three, four, six, seven, or probably even twelve sets of finger-bones on each hand/foot/fin.
5) Species. There are a number of different definitions for the term "species"; what the evidence is for evolution being able to produce a new species depends on which definition you're using. The reproductive concept of species is "a set of organisms that interbreed among themselves but do not breed with members of other species". The phenotypic concept defines a species as a group of organisms that are sufficiently similar to one another and sufficiently different from members of other species; this is probably the closest to our intuitive defintion of the term. A useful definition that makes no assumptions about evolution is: "species are groups of actually or potentially interbreeding natural populations that are reproductively isolated from other such groups".
Okay! So now, class, your assignment is: tell me what we need to go into more detail about. Is this all review? All makes sense? What do you want to talk about?