chromosome rearrangements

8/14/2019 Chromosome Rearrangements

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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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Duplication doubling of a segment of achromosome Tandem Reverse tandem Terminal tandem Position Effect of barring eyes in Drosophila


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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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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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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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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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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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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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chromosome rearrangements

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