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Chapter 15: Large-scale chromosomal changes. Fig. 15-2. Aberrant euploidy (usually polyploidy) and aneuploidy. Cell size typically reflects ploidy. 2N and 4N grapes. Fig. 15-4. Fig. 15-12. Types of polyploidy Autopolyploidy : multiple copies of identical

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Fig. 15-2


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    1. Chapter 15: Large-scale chromosomal changes Fig. 15-2

    2. Aberrant euploidy (usually polyploidy) and aneuploidy

    3. Cell size typically reflects ploidy 2N and 4N grapes Fig. 15-4 Fig. 15-12

    4. Types of polyploidy Autopolyploidy: multiple copies of identical chromosome sets; usually develop normally; cells are proportionately larger than diploid Alloploidy: multiple copies of non-identical chromosome sets; includes genomes of two different species; usually display “hybrid” characteristics

    5. Autotriploids routinely generate aneuploid gametes (usually sterile) Fig. 15-5

    6. Autotetraploids are readily generated by suppressing mitotic spindle Fig. 15-6

    7. Autotetraploids routinely generate aneuploid gametes (usually sterile) Fig. 15-7

    8. Allopolyploids arise from interspecific hybridization + genome duplication Fig. 15-8

    9. Likely origins of modern hexaploid wheat Fig. 15-10

    10. Aneuploidy: 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)

    11. Aneuploidy arises from meiotic nondisjunction, forming aneuploid gametes/spores Fig. 15-13

    12. Aneuploids produce aneuploid gametes/spores Fig. 15-15

    13. Viable human aneuploids are mostly limited to the smallest chromosomes and to the sex chromosomes Examples: trisomy-21: Down syndrome XO(no Y): Turner syndrome; primarily female; only viable human monosomic XXY: Klinefelter syndrome; primarily male

    14. Down syndrome: the clinical manifestations of trisomy-21 Fig. 15-17

    15. The frequency of non-disjunction leading to trisomy-21 (and other aneuploidy) is correlated with maternal age Fig. 15-18

    16. Dosage 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 cell In Drosophila: the activity of each X-linked gene copy is reduced in multi-X cells Thus, “gene balance” problems are alleviated in commonly occurring sex chromosome aneuploids

    17. Chromosomal 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)

    18. Types and origins of chromosomal rearrangements Unbalanced rearrangements Balanced rearrangements Fig. 15-19

    19. Consequences of inversions on neighboring genes Fig. 15-20

    20. Meiotic consequences of inversion heterozygosity Fig. 15-21

    21. Crossingover within inversion • loops result in chromosome • duplications/deletions • Paracentric/Pericentric • Crossover products yield inviable gametes/progeny • non-crossovers predominate • outside markers appear • closer than they really are • crossingover is suppressed Fig. 15-22

    22. Meiosis in translocation heterozygotes can result in duplication/deletion gametes/spores Fig. 15-24

    23. Loops are also seen in synapsed homologs in deletion heterozygotes Deletions behave genetically as multi-gene loss-of-function mutations Fig. 15-28

    24. Deletions are useful in physically mapping small chromosome regions Fig. 15-29

    25. Incidence of chromosome mutations in humans Fig. 15-33

    26. Fig. 15-

    27. Fig. 15-