F24_L_TypesofVariation PDF

What are we trying to explain? http://scienceblogs.com/grrlscientist/2008/01/15/sighted- blind-cave-fishes/ 1 Types of Variation Genotypes, Phenotypes, and evolution 2 1 ...

What are we trying to explain? http://scienceblogs.com/grrlscientist/2008/01/15/sighted- blind-cave-fishes/ 1 Types of Variation Genotypes, Phenotypes, and evolution 2 1  Genotype and Phenotype Trait  Characteristics of an organism - e.g. eye color, hair color, seed shape, etc Genotype  The genetic make-up of the organism Phenotype  The discernible features of an organism 3 1) The relationship between Hey! the genotype and the What’s the phenotype is usually complex big idea!!! 2) So far, we’ve discussed how you get new gene combinations, but what is the ultimate source of variation? Where does the “fuel” for natural selection come from? 4 2  Types of Variation Genotypes, Phenotypes, and evolution Relationship between genotype and phenotype is sometimes simple Complete Dominance E.g. Neurofibromatosis -1 Excessive tissue growth along nerves Potential blindness  Note: Dominant alleles are NOT necessarily more common than recessive If deleterious, usually uncommon 5 Types of Variation Genotypes, Phenotypes, and evolution Relationshipbetween genotype and phenotype is sometimes not so simple 13.15 Incomplete Dominance 6 3  Types of Variation Genotypes, Phenotypes, and evolution Relationshipbetween genotype and phenotype is usually complex  Genes may be linked 13.17  Mendel’s law of independent assortment applies to genes on different chromosomes, or at least far apart on the same chromosome 7 Types of Variation Genotypes, Phenotypes, and evolution Relationship between genotype and phenotype is usually complex  Pleiotropy - One gene may affect many traits  c.f. the recent finding of unexpectedly few human genes  E.g. Coloration and Crossed eyes in Siamese cats, Marfan syndrome 8 4  Types of Variation Genotypes, Phenotypes, and evolution Relationship between genotype and phenotype is usually complex  Epistasis- Genes influence each other’s expression  Very common 13.19 9 Types of Variation Genotypes, Phenotypes, and evolution Relationship between genotype and phenotype is usually complex  Quantitative Traits  Polygenic inheritance - Most traits are affected by many genes - E.g. height See 13.21 10 5  Types of Variation Genotypes, Phenotypes, and evolution Relationship between genotype and phenotype is usually complex  Quantitative Traits  Polygenic inheritance - Most traits are affected by many genes - E.g. height 11 Types of Variation Genotypes, Phenotypes, and evolution 12 6  Types of Variation Genotypes, Phenotypes, and evolution 13 Types of Variation Genotypes, Phenotypes, and evolution Relationship between genotype and phenotype is usually complex  Development - Do identical twins have identical fingerprints? 14 7  Types of Variation Genotypes, Phenotypes, and evolution Relationship between genotype and phenotype is usually complex  Environment - The phenotype is influenced by the environment  E.g.height, PKU Phenylketonuria  The “Norm of Reaction” A very important concept! 15 Sources of Genetic Variation Recombination and independent assortment reshuffle existing variation Where does variation come from? 16 8  Sources of Genetic Variation Recombination and independent assortment reshuffle existing variation Where does variation come from? Mutation  Errorsin repair or synthesis  Damage caused by X-rays or chemicals  Unequal crossing over  Errors in meiosis 17 Sources of Genetic Variation Point mutations  Substitution  Silent - Code for same amino acid  Missense - Code for wrong amino acid E.g. Sickle cell anemia THE FAT CAT ATE THE RAT -> THE FAT CAT ATE THE HAT 18 9  Sources of Genetic Variation Point mutations 19 Sources of Genetic Variation Point mutations  Substitution  Silent - Code for same amino acid  Missense - Code for wrong amino acid E.g. Sickle cell anemia E.g. Osteogenesis imperfecta 20 10  Sources of Genetic Variation Point mutations  Substitution  Silent - Code for same amino acid  Missense - Code for wrong amino acid E.g. Sickle cell anemia E.g. Osteogenesis imperfecta  Nonsense - Prematurely stop translation THE FAT CAT ATE 21 Sources of Genetic Variation Point mutations  Substitution  Insertion/Deletion  Often have major effects - e.g. frameshift mutations THE FAT CAT ATE THE RAT -> THE ATC ATA TET HER AT- 22 11  Sources of Genetic Variation Point mutations Larger scale chromosomal rearrangements  Deletion - E.g. Some Duchenne’s muscular dystrophy  Duplication  E.g. Huntington’s chorea  Repetitions of CAG. O.k. if XX males 24 12  Sources of Genetic Variation Pointmutations Larger scale chromosomal rearrangements  Deletion - E.g. Some Duchenne’s muscular dystrophy  Duplication - E.g. Huntington’s chorea  Repetitions of CAG. O.k. if XX males  XX male mice at right 25 26 13  Sources of Genetic Variation Pointmutations Larger scale chromosomal rearrangements  Deletion - E.g. Some Duchenne’s muscular dystrophy  Duplication - E.g. Huntington’s chorea  Inversion  Translocation - E.g. of SRY gene -> XX males Chromosome number: Non-disjunction  E.g. Down syndrome 27 Sources of Genetic Variation Point mutations Larger scale chromosomal rearrangements Chromosome number  Non-disjunction  E.g. Down syndrome See 12.14 28 14  Sources of Genetic Variation Point mutations Larger scale chromosomal rearrangements Chromosome number  Non-disjunction  E.g. Down syndrome 29 Sources of Genetic Variation Point mutations Larger scale chromosomal rearrangements Chromosome number  Non-disjunction  E.g. Down syndrome  E.g. Polyploidy 30 15  (Auto)polyploidy 31 Summary The relationship between the genotype and the phenotype ranges from simple to very complex Truly Mendelian inheritance is just a small subset of patterns of inheritance Recombination and independent assortment reshuffle existing variation, creating new combinations of genes Variation arises from mutations 32 16