Chapter 5 Evol Bio PDF
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Summary
This document explores various types of biological variation, including genetic, environmental, and genotype-environment interactions. It discusses proteins, genetic material (DNA and RNA), and how genes influence traits, focusing on the mechanisms behind variation in organisms and the role of genetic and environmental factors in evolution. This document serves as a good starting point for understanding basic evolutionary biology.
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Variation Among Individuals Variation among individuals is the raw material for evolution Thamnophis Asteraceae Human Popula1on Three Kinds of Variation three different kinds of variation amo...
Variation Among Individuals Variation among individuals is the raw material for evolution Thamnophis Asteraceae Human Popula1on Three Kinds of Variation three different kinds of variation among individuals These are gene1c varia1on, environmental varia1on, and genotype-‐by-‐environment interac1on. The Machinery of Life: Proteins Different kinds of cells are dis1nguished by the proteins they make The Machinery of Life: Genetic Material Organisms carry instruc1ons for how to build the proteins they use, as well as for when, where, and in what quan11es to make them, in their gene1c material. The gene1c material is RNA in some viruses. In other viruses, and all cellular forms of life, the gene1c material is DNA. The Machinery of Life: Genetic Material Genes in organisms are embedded in long DNA molecules called chromosomes. A typical chromosome carries numerous genes. The physical loca1on of a gene on a chromosome is called the gene’s locus. Some of the genes on human chromosome 7 The Machinery of Life: Genetic Material The Machinery of Life: From Genes to Proteins What is the the mechanisms responsible variations among individual Gene1c varia1on is the result of differences among individuals that are encoded in their DNA. Environmental varia1on arises when external factors influence how much protein is made from par1cular genes, or how the proteins work. Genotype-‐by-‐environment interac1on is the result of differences among individuals that are encoded into their DNA and that make them differ in their sensi1vity to environmental influences. Genetic Variation Albinism among the Hopi Na1ve Americans. In this photograph, taken about 1900, the Hopi girl in the center has albinism. variation in the perception of taste: PTC Taste receptor proteins have diverse shapes and chemical proper1es. Each kind of taste receptor protein binds with a subset of the chemicals in food, corresponding to sweet, sour, salty, umami (savory), and biSer flavors variation in the perception of taste: PTC One way to demonstrate this varia1on is to offer people small quan11es of the chemical phenylthiocarbamide (PTC) variation in the perception of taste: PTC The one that binds PTC is TAS2R38, encoded by a gene on chromosome 7 The most common TAS2R38 alleles, named for the amino acids they specify at the variable sites, are AVI and PAV. Considering just alleles AVI and PAV, the three possible genotypes are AVI/AVI, AVI/PAV, and PAV/ PAV variation in the perception of taste: PTC The human life cycle (a) We spend most of our lives in a diploid phase, carrying a complete set of chromosomes received via the egg and a complete set received via the sperm. Each gamete we make receives one member of each chromosome pair. (b) We can thus use a PunneS square to calculate the odds that a zygote will have a par1cular genotype Genetic Variation and Evolution We have looked at gene1c varia1on among HIV virions in their suscep1bility to the an1retroviral drug AZT as well as gene1c varia1on among humans in the suscep1bility to HIV infec1on. We have considered gene1c varia1on among s1cklebacks in the extent of body armor and gene1c varia1on in fruit size in tomatoes. Environmental Variation Water Flea vs Phantom Midges Our example of environmental varia1on concerns a prey species, the water flea, and its predator, a larval insect. Water fleas are 1ny freshwater crustaceans that inhabit lakes and ponds all over the world (Lampert 2011). Among the traits that make water fleas useful for the study of environmental varia1on is that when condi1ons are auspicious they reproduce by cloning, switching to sexual reproduc1on only when condi1ons deteriorate. Also useful is that certain environmental cues trigger changes in their morphology, physiology, and behavior. Water Flea vs Phantom Midges Daphnia pulex is capable of developing a morphology that is well defended against phantom midges. It can nearly double the strength and thickness of its carapace and grow ridges, called neckteeth, on the back of its head Environmental Variation and Evolution A bacterium making equal amounts of both versions of GFP would be yellow, a cell making more of one version would be green, and a cell making more of the other version would be orange. The explana1on for the diversity of colors in the photo is random varia1on in the interac1ons between the promoters and the regulatory proteins that ac1vate and deac1vate them. Genotype-‐by-‐ Environment Interaction Genotype and temperature inGluence sex in leopard geckos (a) A leopard gecko (Eublepharis macularius). (b) Individuals incubated at intermediate tempera-‐ ture are more likely to be male. Development along the female versus the male pathway involves changes in the production of a variety of proteins Expression of the gene Sox9 in the gonad ceases earlier in leopard geckos developing as females than as males Sox9 encodes a transcrip1on factor that directs the expression of other genes and thus commits the gonad to being a tes1s versus an ovary. Genotype-‐by-‐Environment Interaction: Serotonin Transporter Gene Genotype-‐by-‐Environment Interaction: Serotonin Transporter Gene Among people with genotype ll for the serotonin transporter gene, maltreatment in childhood has liSle effect on the probability of major depression in early adulthood, whereas among people with genotype ss maltreatment increases the probability of depression substan1ally Genotype-‐by-‐Environment Interaction: Phenotypic Plasticity An organism that develops different phenotypes in different environments is said to exhibit phenotypic plas1city. When popula1ons harbor gene1c varia1on for environmental sensi1vity, popula1ons can evolve greater or lesser plas1city. Insect genotype-‐ by-‐environment interac1on (a) A normal tobacco horn-‐ worm. (b) A black mutant. (c) Some black mutants turn green a_er heat shock. Where New Alleles Come From The structure of the genetic material Mutation due to DNA Alteration: Spontaneous Deamination Mutation due to DNA Alteration: Premutations DNA altera1ons s1ll suscep1ble to repair, are known as premuta1ons How Mutations Alter Protein Function cell makes a protein from the instruc1ons encoded in a gene, it follows a two-‐step process: TRANCRIPTION & TRANSLATION How Mutations Alter Protein Function synonymous (or silent) subs1tu1on -‐ a muta1on leaves the encoded protein unaltered nonsynonymous (or replacement) subs1tu1on -‐ muta1on that changes the amino specified by a codon How Mutations Alter Protein Function synonymous (or silent) subs1tu1on -‐ a muta1on leaves the encoded protein unaltered nonsynonymous (or replacement) subs1tu1on -‐ muta1on that changes the amino specified by a codon How Mutations Alter Protein Function Where New Genes Come From Two mechanisms of gene duplication A New Gene Generated by Unequal Crossing Over Phylogeny of RNASE1 genes. RNASE1 reac1on norms. Paralogous vs Orthologous A New Gene Generated by Retroposition chondrodysplasia, the short-‐legged condi1on characteris1c of corgis, dachshunds, bassets, and a variety of other breeds on chromosome 18, a duplicate copy of the gene for fibroblast growth factor 4 (fgf4) is found. Possession of the duplicate is strongly associated with chondrodysplasia A New Gene Generated by Retroposition hhsh New Genes from Scratch C22orf45 is a gene of unknown func1on unique to humans. It is transcribed in a variety of 1ssues, and its mRNA is known to be translated into protein. A new human gene from noncoding DNA. In other apes and in macaques, the sequence homologous to the human gene C22orf45 contains a premature stop codon Chromosome Mutations Inversions Chromosome inversions o_en result from a mul1step process that starts when radia1on causes two double-‐strand breaks in a chromosome. A_er breakage, a chromosome segment can detach, flip, and r e a n n e a l i n i t s o r i g i n a l loca1on. W h e n i n v e r s i o n s a r e heterozygous, the inverted s e q u e n c e s c a n n o t a l i g n properly when homologs synapse during prophase of meiosis I. Inversions in Drosophila Drosophila subobscura is a fruit fly na1ve to western Europe, North Africa, and the Middle East, and has six chromosomes. Five of these chromosomes are polymorphic for at least one inversion. Biologists have known since the 1960s that the frequencies of these inversions vary regularly with la1tude and climate. This type of regular change in the frequency of an allele or an inversion over a geographic area is called a cline. But is the cline really the result of natural selec1on on the supergenes? Or could it be a historical accident, caused by differences in the founding popula1ons long ago? Inversions in Drosophila From Old world to New world Of the 80 inversions present in Old World popula1ons, precisely the same subset of 19 is found in both Chile and Washington State. This is strong evidence that the clines result from natural selec1on and are not due to historical accident. Inversions in Drosophila Which genes are locked in Research by George the inversions, and how do Gilchrist and colleagues they affect adapta1on to (2004) has confirmed that changes in climate? pronounced and parallel clines in body size exist in fly popula1ons from North America, South America, and Europe. alleles in the inversions affect body size, and that natural selec1on favors large flies in cold, wet climates and small flies in hot, dry areas. Genome Duplication if homologous chromosomes fail to segregate during meiosis I or if sister chroma1ds do not separate properly during meiosis II, the resul1ng cells may have double the number of chromosomes of the parent cell. Organisms with more than two chromosome sets are said to be polyploid There are at least two reasons that polyploidy is an important type of mutation in evolution First, it can lead to new species being formed. Second, it alters cell size, cell geometry, and gene dosage, and thus may endow individuals with new phenotypes that allow them to colonize and adapt to new environments. Most allopolyploids arise from hybridization between two species followed by chromosome doubling. Polyploidy and Speciation Genome Duplication and Adaptation: Achillea borealis Jus1n Ramsey (2011) tested the hypothesis that polyploidy facilitates the coloniza1on of, and adapta1on to, new environments by performing a common garden experiment with wild yarrow Tetraploid popula1ons live in coastal grasslands, conifer forests, and mountain meadows. Hexaploid plants live in sand dunes and oak woodlands. Genome Duplication and Adaptation: Achillea borealis Ramsey grew tetraploid plants, first-‐genera1on hexaploid plants from tet-‐ raploid parents (neo-‐hexaploids), and hexaploid plants—all from wild popula-‐ 1ons—next to each other in sand dunes. He monitored them for three years. Survival of plants with different ploidy in a common garden in dunes. Flowering 1me distribu1ons in the same plants.