Slide 1Slide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 224th edition: p. 289-300, 3083rd ed: p. 297-308• germ-line mutations and heritable changes• gene alterations and genome evolution• the generation of gene families• mechanisms for generating new geneticcombinationsChapter 9: How Genes and Genomes EvolveThe germ line is set aside early in developmentThe effect of a mutation depends on the cell lineage in which the mutation occurs.• if the mutation occurs in a somatic cell, only the progeny of that cell will be affected in the individual in which the mutation occurred• if the mutation occurs in a germ cell, the mutation does not affect the individual but may be passed on to the next generation (= results in a heritable trait)Germ line: the cell lineage in a multicellular organism thatcontributes to the formation of a new generation byproducing gametes (sperm or eggs).Somatic cell (body cell): any cell in a multicellular organismthat is not a germ line cell.Germ line vs. Somatic cellsGerm line vs. Somatic cellsAltered productAltered expressionBeginning of a gene familyGenetic changes that contribute to gene alteration and genome evolution1)3)2)4)5)Gene acquisition6)The effect of changes in regulatory regionsExample: both species express gene 1 which codes for a transcription regulator• in organism A, the regulatory DNA sequence for thistranscription regulator is in front of gene 3, • the related organism B, the same regulatory DNAsequence is in front of gene 2 in result: organisms follow different developmental pathwaysClosely-related species with the SAME sets of developmentally-related genes may take very DIFFERENT developmental pathways if regulatory DNA sequences differ.The effect of changes in regulatory regionsGene families are groups of genes that originate by duplication from a common ancestor.• family members are similar in structure and/or functionClassic example: The globin gene family• multiple genes code for hemoglobin subunits• different members are expressed during fetal, embryonic,and adult stages• they also include pseudogenes (non-functional genes)Gene Duplication leading to Gene familiesHemoglobin transports O2 and CO2 in the circulatory system.• the adult version contains 4 subunits: 2 alpha and 2 beta• heme group: iron-containing molecule in globin subunitHemoglobinThe human globin gene family Different globin proteins have different affinities for O2The evolution of theglobin gene familyGene duplication by unequal crossing overShort repeated sequences within homologous chromosomescan cause misalignments and unequal crossing over.• these short repeated sequences are non-coding conservedsequences scattered throughout the genome• unequal crossing over results in chromosomes with altered size and genetic content:- one chromosome has an extra copy of the gene- the other chromosome has lost the gene(interspersed repeats)The duplication of entire genomesIf a germ cell fails to divide after DNA replication, the doubling of the genome may be passed on to gametes and eventually to the progeny.The Xenopus genus:• X. tropicalis (top) has a diploid genome• X. laevis (bottom) duplication of a whole genome resulted in a tetraploid speciesGenetic rearrangement by mobile genetic elementsThe transposition of eukaryotic mobile genetic elementscan mediate gene rearrangement• if two similar mobile genetic elements insert near each other in a chromosome, the transposition mechanism may use the ends of the two different elements, resulting in transposition of the entire segment of the chromosome between the two mobile elements.• if the transposed segment includes an exon (exon 2 from GENE A), its insertion into a second gene (GENE B) would create a new version of that gene (new GENE B) = exon transposition.Exon transposition bymobile genetic elementsGenetic rearrangement by mobile genetic elementsThe transposition of eukaryotic mobile genetic elementscan alter regulatory sequences.• the rearrangement of regulatory sequences can alter thetissue-specific pattern of gene expressionAlteration of regulatory sequencesby mobile genetic elementsAlteration of regulatory sequences of the Antennapediagene caused by insertion of a mobile genetic element(P-element) causes the gene to be ectopically expressed in the head.As a result, the antennae are transformed into legs.Ectopic expression of AntennapediaHomeotic Transformation:one body part is replaced by a body part normally found in another regionGenetic changes that contribute togene alteration and genome evolutionGene acquisitionConjugation is the transfer ofgenetic information (via a plasmid) from one cell to another through a sex pilus. The result is genetic recombination without reproduction. Bacterial