Slide 1Slide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Fig. 15-2Chapter 15: Large-scale chromosomal changesAberrant euploidy (usually polyploidy) and aneuploidyFig. 15-12Cell size typicallyreflects ploidyFig. 15-42N and 4N grapesTypes of polyploidyAutopolyploidy: multiple copies of identical chromosome sets; usually develop normally; cells are proportionately larger than diploidAlloploidy: multiple copies of non-identical chromosome sets; includes genomes of two different species; usually display “hybrid” characteristicsFig. 15-5Autotriploids routinely generate aneuploid gametes(usually sterile)Fig. 15-6Autotetraploids are readily generatedby suppressing mitotic spindleFig. 15-7Autotetraploids routinely generate aneuploid gametes(usually sterile)Fig. 15-8Allopolyploids arise from interspecific hybridization + genome duplicationLikely origins of modern hexaploid wheatFig. 15-10Aneuploidy: extra or missing chromosomes (less than an entire haploid set)Examples:monosomy: 2n – 1(one chromosome has no homolog)trisomy: 2n + 1(three homologs for one chromosome)Aneuploidy arises from meiotic nondisjunction, forming aneuploid gametes/sporesFig. 15-13Aneuploids produce aneuploid gametes/sporesFig. 15-15Viable human aneuploids are mostly limited to the smallest chromosomes and to the sex chromosomesExamples:trisomy-21: Down syndromeXO (no Y): Turner syndrome; primarily female;only viable human monosomicXXY: Klinefelter syndrome; primarily maleDown syndrome: the clinical manifestations of trisomy-21Fig. 15-17The frequency of non-disjunction leading to trisomy-21 (and other aneuploidy) is correlated with maternal ageFig. 15-18Dosage compensation: mechanism for making X-linked gene expression equal in females (with two X chromosomes) and in males (with one X chromosome)In mammals: only one X chromosome is active in each cellIn Drosophila: the activity of each X-linked gene copy is reduced in multi-X cellsThus, “gene balance” problems are alleviated in commonly occurring sex chromosome aneuploidsChromosomal rearrangements• Arise from double-strand DNA breaks• Such artificial ends are very transient and rapidly join together• Rejoining may restore the chromosome or may result in any imaginable combination of joined fragments• Recovery of those products follows certain rules:1. Each product must have no more nor less than one centromere (a mitotic and meiotic “must”)2. Viability of the gametes/spore/zygote following meiosis is subject to gene balance effects(segmental aneuploids are usually poorly viable)Fig. 15-19Types and origins of chromosomal rearrangementsUnbalancedrearrangementsBalancedrearrangementsFig. 15-20Consequences of inversions on neighboring genesFig. 15-21Meiotic consequences of inversion heterozygosityCrossingover within inversion loops result in chromosome duplications/deletionsParacentric/PericentricCrossover products yield inviable gametes/progeny• non-crossovers predominate• outside markers appear closer than they really are• crossingover is suppressedFig. 15-22Meiosis in translocation heterozygotes can result in duplication/deletion gametes/sporesFig. 15-24Loops are also seen in synapsed homologs in deletion heterozygotesDeletions behave genetically as multi-gene loss-of-function mutationsFig. 15-28Deletions are useful in physically mapping small chromosome regionsFig. 15-29Fig. 15-33 Incidence of chromosome mutations in humansFig. 15-Fig.