Duplications Bar eye caused by duplication Duplications source of evolutionary novelty Duplication is a source of new genes over evolutionary time e g gene families like globins and MHC genes Structural Changes Deletions deficiencies Duplications Inversions Translocations Inversions Inversions Suppress Recombination Organisms carrying an inversion tend to undergo little crossing over in the inversion region in both inverted and noninverted chromosomes If there is crossing over half the chromatids involved in crossing over will produce non viable gametes Can be a cause of Inversions and evolution If loci inside an inversion affect a single trait or suite of related traits this means they ll be inherited together and allele combinations won t be broken up by recombination A suite of tightly linked loci that affect a single trait is collectively known as a SUPERGENE mimicry coloration in some species of butterflies snail shell color pattern some species Structural Changes Deletions deficiencies Duplications Inversions Translocations Robertsonian Translocation Familial Down Syndrome Position Effect In some translocation mutations the new position of the gene can affect the rate of its transcription and translation For example if a highly transcribed gene is translocated to a region close to tightly coiled inactive heterochromatin it can sometimes be partially engulfed by that heterochromatin This will result in a failure of the gene to be expressed in the cells where the heterochromatin coils over the translocated gene This can be seen in position effect variegation in our old pal Drosophila Chromosome Evolution Human Chimpanzee Horse Cat Chicken Geometrid moth Drosophila mel Ant Myrecia pilosula Tomato Horsetail Pink bread mold 2n 46 48 64 38 78 224 8 2 24 216 14 n 23 24 32 19 39 112 4 1 12 108 7 Evolutionary change in chromosome number Centromere fusion two acrocentric chromosomes become fused at or near their terminal centromeres creating a single large chromosome Result Often evidence of this in closely related species Compare the NF fundamental number the number of chromosome arms visible at metaphase Or compare sequence data Centromere fission In this case the chromosome splits at the centromere creating two chromosomes from one Result QuickTime and a TIFF LZW decompressor are needed to see this picture Synteny Polyploidy Autopolyploidy Allopolyploidy Triploid Tetraploid P 2n 2n P G n 2n G F1 F1 2n 2n Many plants are polyploids of flowering plants are of polyploid origin In many genera different species will have different ploidy levels multiples of a base number representing a series of polyploids In the genus Chrysanthemum different species have chromosome numbers of 2n 18 36 54 72 90 and 198 all multiples of a base chromosome number of 9 Some autopolyploids Winesap apples Commercial bananas Seedless watermelons Cultivated tiger lily Allopolyploidy Resutls from hybridization between different species Bread wheat oats cotton tobacco strawberries coffee Xenopus frogs Allopolyploids Bread wheat Xenopus frogs Speciation by Polyploidization Some species are sufficiently closely related that their genes when combined in a hybrid individual provide the necessary information for a viable organism but not for that organism to undergo normal meiosis Homo sapiens 2n 46 Pan troglodytes 2n 44 Hybrid between the two would be 2n 45 BUT THIS HAS NOT HAPPENED DESPITE WHAT THE WEEKLY WORLD NEWS WILL TELL YOU Speciation by Polyploidization Some species are sufficiently closely related that their genes when combined in a hybrid individual provide the necessary information for a viable organism but not for that organism to undergo normal meiosis Homo sapiens 2n 46 Pan troglodytes 2n 44 Hybrid between the two would be 2n 45 BUT THIS HAS NOT HAPPENED DESPITE WHAT THE WEEKLY WORLD NEWS WILL TELL YOU Artificially Produced New Species Brassica oleracea x Raphanus sativa Both species 2n 18 n 9 chromosomes not homologous X hybrid has 18 chromosomes but meiosis is abnormal Nondisjunction in a meristematic cell 36 chromosomes The cell is said to be allopolyploid allotetraploid Normal meiosis These plants are self fertile so can produce offspring even if there is only one such individual New genus species was named Raphanobrassica Unfortunately the hybrid combines the root of a cabbage with the flower head of a radish rather than the reverse Rhaphanobrassica Polyploidy in Animals Animals can also produce allopolyploids e g horse x donkey mule lion x tiger liger or tigon In mammals these crosses tend to be sterile but many fish and reptile species are thought to have arisen as polyploids e g Why less common in animals Many animals have chromosomally determined sex and polyploidy interferes with this Most animals have several isolating mechanisms geographic temporal behavioral etc that tend to prevent natural interbreeding between species Many plants have meristematic tissue throughout their lives and are self fertile In plants about 5 out of every 1000 gametes produced is diploid
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