Primate Behavioral Ecology Genetics, Protein Synthesis, and Natural Selection

Transcription

1 Primate Behavioral Ecology Genetics, Protein Synthesis, and Natural Selection

2 Darwin s Biggest Scientific Problem Darwin realized that natural selection for specific traits could lead to changes in species through time. However, Darwin lacked information on how these traits were passed from generation to generation.

3 Genetics Mendel was the first to explore the units of inheritance: genes. Gregor&Mendel&(1822/1884)&&

4 What do GENES do? They control the production specific PROTEINS in living things By stringing up small amino acid molecules into long protein strands

5 Genetics and Protein Synthesis; Bodies are made of protein and other stuff

6 Organisms Components Organism = a living thing Living things are made of matter What kind of matter? Molecules Proteins, e.g., collagen, enzymes, etc. there are some exceptions, e.g., viruses--but they are not relevant to our simplified introductory discussion in this class--take upper division biology classes if you are interested Also: water, carbohydrates, fats, vitamins/minerals, DNA (nucleic acids), etc., Proteins are long molecules that are folded over on themselves The components of protein molecules are smaller molecules called amino acids (AAs)

7 Amino Acids There are 20 kinds of AAs that make up all the proteins that organisms have Such as: alanine, asparagine, methionine Made of Hydrogen, Oxygen, Nitrogen, Carbon, (HONC) and Sulfur (S only in methionine and cysteine)

8 Amino Acids AAs are small molecules, but when strung up and folded over on themselves to form a protein, they can be quite large AAs are attached by peptide bonds AAs are molecules whose properties are determines by their electrochemical configurations

9 Amino acid strand Each AA is like a bead on a necklace; electrochemical interactions among neighboring AAs cause the strand to fold over on itself in specific ways. The folded strand is a protein. Different AA sequences will make different proteins.

10 Protein Proteins interact with other substances (including other proteins) in specific ways that are determined by their electrochemical properties. There are only 20AAs out there a finite number (though in actuality the story is more complex than this) Different lengths and permutations of the AAs that make up AA strands can lead to countless varieties of proteins

11 Protein Functions Structural proteins (collagen in skin, keratin in hair and nails, proteins that make up muscle tissue, etc.) Transport proteins (hemoglobin is a blood cell protein that transports oxygen to body tissues) Enzymes: proteins that catalyze (speed up) chemical reactions in the body Immune functions Signaling functions: E.g., neurons in your brain communicate with each other; these neurons are proteins (and other substances)

12 Proteins From where to organisms get the AAs needed for body maintenance and growth?

13 Food! Foods are typically living (or formerly living) substances What substances are in our food? Lichtenstein 1962 Meat

14 Components of living things (like food) Protein: the stuff living things are made of, including structural proteins like collagen, enzymes, etc. Also water, carbohydrates, fats, vitamins/minerals, DNA (nucleic acids), etc. Proteins are long molecules that are folded over on themselves The components of protein molecules are smaller molecules called amino acids (AAs)

15 Proteins to AAs Organism A eats foreign protein that makes up organism B Organism A breaks Organism B proteins into AAs: digestion Organism A s DNA restrings raw AAs up into Organism A proteins Organism A s DNA = blueprints Organism B = the raw building blocks of proteins

16 Amino Acids to Proteins genes

17 Genes Proteins Genes determine what proteins get built from those raw AA molecules Genes are protein-coding units of DNA You eat proteins of other living things, and break the protein into amino acids; then, genes in your DNA re-string those amino acids into proteins that YOU need to survive and reproduce Bodies are made of proteins (fat and carbs and water are essentially there to service these proteins) Genes also code for enyzmes, which are proteins that regulate everything, including development Other parts of DNA do not code for proteins, and have either no function (e.g. hitchhiker DNA), or function for self-regulation, and other tasks take advanced biology classes to learn about these very cool things DNA does What is DNA?

18 DNA Deoxyribonucleic acid A long molecule with a small number of constituent molecules Shape is a double helix think of a ladder that is twisted

19 A sugar-phosphate backbone, (I.e., the sides of the ladder), and rungs made up of paired nucleic acids There are 4 nucleic acids: adenine (A), thymine (T), cytosine (C), and guanine (G) [don t worry about uracil (U), for the purposes of this class Note these are not AAs A only bonds to T C only bonds to G A-T and C-G bonds are weak Sugar-phosphate bonds are strong Lots of zipping action DNA

20 Genes to Proteins Protein synthesis An elegant process brief whiteboard illustration (RNA, Uracil, ribosomes: do not worry about these for this class) Upshot: the sequence of nucleotides in DNA determines the sequence of AAs in protein manufacture (nucleic acid sequence maps to AA sequence, but not one-to-one, and redundancy is built into the system) In other words, your DNA determines what proteins get built out of the AAs that your body extracts from the foreign proteins you eat

21 Genes Proteins Bodies + DNA molecule Amino acid molecules Amino acid strand Protein Cell parts, cells, and tissues Organ Body

22 DNA-Supercoil-Chromosome

23 Genes vs. Alleles Genes: protein-coding regions of an organism s DNA Alleles: different forms of a gene at a particular spot ( locus ) on the DNA; different allele have slightly different DNA sequences, and make slightly different versions of a protein Here, the gene = eye pigment; with a few exceptions, we all have eye pigment, and the gene for this pigment is at the same spot on our DNA strand for every person Allele = brown eyes vs. blue eyes: even though we all have eye pigment protein, different people can have different versions of the eye pigment protein

24 Brown sciencetech/article / The-eyes-The-iris-picturedremarkable-incredible-closeshots.html

25 Blue

26 Green

27 Green?

28

29 Allele Frequencies Allele frequency = the proportions of different alleles among all the individuals in a specific population (in this room, allele frequencies underlying eye color might be different from frequencies in a Scandinavian population, which might have more blue and green eyes people, or a population whose ancestors lived near the equator, which might have more brown eyed people) Whiteboard exercise on allele frequencies of eye color in this class, in order to illustrate what evolution is; assume, for now, that human eye color is determined by a single gene with 3 possible alleles: brown, blue, and green How many people total? How many people with each of the (roughly) 3 colors of eyes in this classroom?

30 Exercise: Eye Color Allele Frequencies 100 people in class (assume, for now, that human eye color is determined by a single gene with 3 possible alleles: brown, blue, and green) 60 people have brown eyes 30 people have blue eyes 10 people have green eyes The current generation of our classroom population, G1, has the allele frequencies: 60% brown, 30% blue, and 10% green Everyone has the opportunity to reproduce. Many of us do. The next generation s allele frequencies are

31 Exercise: Eye Color Allele Frequencies The allele frequencies in the next generation, G2, are again 60% brown, 30% blue, and 10% green This means that allele frequencies have NOT changed over generations: evolution has NOT occurred from generation 1 to generation 2. Now this 2 nd generation has the opportunity to reproduce. Many do. The allele frequencies in the next generation, G3, are

32 Exercise: Eye Color Allele Frequencies The next allele frequencies in G3 are now 90% brown, 5% blue, and 5% green (they had been 60% brown, 30% blue, and 10% green in G2) This means that allele frequencies HAVE changed over generations: evolution HAS occurred from G2 to G3. Evolution is defined as a change in allele frequencies in a population over generations

33 Exercise: Eye Color Allele Frequencies G3 allele frequencies are 90% brown, 5% blue, and 5% green Now this generation has the opportunity to reproduce. Many do. The next allele frequencies in the next generation, G4, are 90% brown, 5% blue, 4% green, and 1% purple This means that allele frequencies HAVE changed over generations: evolution HAS occurred between G3 and G4. But where did this new purple allele come from?

34 Mutations! Where do new, different alleles come from? Mutations. Mutations are random mistakes in the molecular sequence of DNA, which can lead to changes in proteins that get built A change in the DNA sequence of a gene will cause a change in the protein that gets built ATGCAAAATCGG=green eye pigment protein ATGCAACATCGG=purple eye pigment protein Origins of mutations include radiation (x-rays, solar rays, other cosmic rays, nuclear waste), various non-living substances (asbestos, cigarette smoke), living substances (viruses), unknown causes, etc. Only heritable mutations are relevant to the evolutionary process because evolution is a process that occurs over generations Not all mutations that occur in living things are heritable; there is an important difference in the heritability of mutations in multi-celled vs. single-celled organisms...

35 Genes (DNA segments) Genes are protein-coding regions of an organism s DNA (1) They direct protein synthesis (2) They ALSO replicate, or reproduce, over generations, as they are passed from parents to offspring (offspring inherit their parents genes) (a) in single-celled organisms, one mother (or parental ) cell s genes double then divide and are passed on to two daughter (or offspring ) cells (the parent cell no longer exists its body s proteins now make up the bodies of two offspring) (b) in multicelled organisms, there are two kinds of cells: somatic cells and germ cells: (i) somatic cells (such as human skin cells), live only as a part of the parental body; somatic cell genes build proteins for the parent s body; reproduction of somatic cells involves gene replication, but the new cells remain a part of the parental body (ii) germ cells (such as sperm and eggs) are housed in the parental body; then, at the time of reproduction, a germ cell leaves the parental body, and develops a new multicelled body of its own THE point: only germ cell genes can make it into the next generation for multicelled organisms like humans freshwater paramecium (single-celled) red-tailed hawk (multicelluled)

36 Reproduction in Single vs. Multi-celled Organisms single-celled mother multi-celled mother Somatic line cells All genes reproduce by doubling ½ of reproduced genes passed to each of two identical, singlecelled daughters *The somatic line cells ARE the germ line cells Germ line cell multi-celled daughter At reproduction, germ line cell leaves mother s body and multiplies, creating new somatic cells for its daughter body, and, at some point, a subsequent germ line of cells that the daughter can transmit into the next generation; germ line = eggs and sperm in sexually-reproducing species Germ line cell

37 Heritability in Multi-celled Organisms Mutation must be in germ line of cells to be passed to offspring; only mutations in the germ line heritable, and thus subject to the process of evolution Mutations in the somatic line can lead to new proteins (usually bad) being built in the maternal body ( cancer ), but these alleles are NOT passed to the next generation; they die with the mother s body Germ line cell

38 Heritability in Single-celled Organisms X-ray radiation causes a mutation in this parental gene (green) x& Somatic and germ line are the same, so all mutations in parent will be passed to offspring; that is, all mutations are heritable

39 Evolution Heritable alleles are passed from parent to offspring over generations. Evolution is change in allele frequencies in a population over generations. Natural Selection is one type of evolution (there are 4 )

40 Definitions and Types of Evolution There are 4 causes of changes in the allele frequencies in a population over time: (1) Migration of individuals in or out of a population can cause the allele frequencies to change (e.g., a bunch of red eyed people join our population in the next generation) (2) Mutations can cause allele frequencies to change (e.g., one person s child happens to be born with a mutated allele that produces purple eyes) (3) Genetic drift occurs when a random event NOT related to one s alleles alters the allele frequencies in a population (e.g., the 5 blue eyed people in our population happen to fall off a cliff, erasing all blue genes from the subsequent generation and having blue eyes had NOTHING to do with falling) (4) Natural selection

41 Natural Selection Natural selection is change in allele frequencies in a population over generations due to the causal effects alleles have on reproduction Natural Selection is nonrandom, differential propagation of alleles

42 Natural Selection If reproducing entities exist, if variations are heritable, and if variations have reproductive consequences, then over time, the entire population will come to possess the reproductively superior variation *note that for multicelled organisms, these variations are in the germ line of cells In terms of genetics: Over generations, alleles that build proteins that promote their own reproduction relative to the rest of the alleles in the population will reproduce more than the population s alleles that build proteins that hinder their own reproduction. The best-reproducing genes, and the traits they build, reproduce best. Simple, and NOT circular, as time only goes in one direction.

43 The Modern Evolutionary Synthesis A union of ideas from different branches in biology that provides a logical account of the physical process of evolution; links are made over time with regard to: 1850s-1890s: Darwin s ideas Early 1900s: Mendel s (earlier) work was rediscovered and incorporated Starting in 1920s: work by population geneticists Haldane, Wright, Morgan, and others Further advances in the understanding of DNA (Watson, Crick, and Franklin) in mid 1900s In later 1900s: ideas elaborated by Hamilton, Maynard-Smith, and Williams Also in late 1900s; ideas about genes, evolution, and adaptations and particularly their roles in human life were popularized by Dawkins, challenged by Gould, etc. Today, the synthesis is accepted by most working biologists