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Chromosome rearrangements
and
change in chromosome number
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Chromosomal Mutations
Deletion part of the chromosome ismissing Starts with breaks in the chromosome Radiation, heat, viruses, chemicals, etc. May cause an unpaired loop May give rise to pseudodominance Cri-du-chat syndrome (Chrom. #5)
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Chromosomal Mutations
Duplication doubling of a segment of achromosome Tandem Reverse tandem Terminal tandem Position Effect of barring eyes in Drosophila
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Chromosomal Mutations
Inversion results when a segment of achromosome is excised and thenreintegrated in an orientation 180 degreesfrom the original orientation. Pericentric inversion Paracentric inversion Resulting from a dicentric bridge
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Chromosomal Mutations
Translocation change in position of chromosome segments and the genesequences they contain to a differentlocation Nonreciprocal intra chromosomal Nonreciprocal inter chromaosomal
Reciprocal interchromosomal
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Variation in ChromosomalNumber
Euploidy the correct number of sets of chromosomes in an organism.
Monoploidy only one set of chromosomeswhen there should be more: Male wasps, ants, and bees are monoploids
because they develop from unfertilized eggs Used in plant-breeding experiments/colchicine
(inhibits mitotic spindle)
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Variation in ChromosomalNumber
Polyploidy having three or more sets of chromosomes Usually occurs due to a breakdown of the
mitotic spindle Usually occurs in plants (self-fertilization) Even numbered polyploids have a better
chance of being fertile than odd numberedpolyploids
In humans, triploidy is usually lethal.
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Variation in ChromosomalNumber
Polyploidy (continued) Autopolyploidy
All sets of chromosomes originate in the samespecies/defect in meiosis
Example a diploid gamete fuses with ahaploid gamete to produce a triploid zygote
(bananas and seedless fruit)
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Variation in ChromosomalNumber
Polyploidy (continued) Allopolyploidy
Sets of chromosomes originate from different speciesthough usually related
Because of differences between chromosomes, thehybrid, no crossing over occurs and no viablegametes produced making hybrids sterile
Occasionally, two sets of different chromosomes willdouble, producing tissues of 2N + 2N 2 / produces fullyfertile allotetraploid, 2N + 2N 2, plants
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Variation in ChromosomalNumber
Aneuploidy variation in the number of chromosomes Nullisomy - loss of one homologous
chromosome pair; 2N 2 Monosomy loss of a single chromosome;
2N 1 Trisomy single extra chromosome; 2N + 1 Tetrasomy extra chromosome pair; 2N + 2
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Changing to Chromosome number or ploidyThis system counts what is there before duplication
Euploids(complete sets of chromosomes)
Aneuploid
Incomplete set or extra
Monoploid (x)
Trisomy(2n+1)
Monosomy(2n-1)
Diploid (2x)
Triploid (3x)
Tetraploid (4x)
Polyploid
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Aneuploidy is harmful, polyploidy may be tolerated:
Balance of gene products (RNA, proteins) is important.
Some polyploids you might know: 1 out of 3 flowering plantsbananas (triploid)coffee, peanuts, McIntosh apples, Grapes (tetraploid)wheat (hexaploid)strawberries (diploid-octaploid)
Unusual in most animalsFound in lizards, amphibians and Fish
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