CHROMOSOME MUTATION: CHANGES IN STRUCTURE & NUMBER

2/3/92, 2/1/95, 1/29/96, 1/31/97, 1/30/98, 28 Jan 00, 29 Jan 01, 3 Feb 03, 3 Feb 06, 1 Feb 08

gmslg (7th) p. 523-576, 9^th: 555-588

Cytogenetics: centromere position:                     telocentric,        at end

                                                                              acrocentric,       near end

                                                                              metacentric,      near middle

                                                                              acentric:            without centromere

heterochromatin: densely stained regions of chromosomes, vs euchromatin, poorly stained

In Diptera, certain tissues replicate chromosomes many times, hold homologs together = polytene

Giant chromosomes formed by endomitosis, cells never divide

chromocenter (coalescence of heterochromatic area around centromeres of all four) (P. 89)

Banding patterns (each band = more than single gene): puffed Balbiani rings show regions of great activity

Ends of chromosomes very reactive, attach to ends of other broken ends (not telomeres)

CHANGES IN STRUCTURE: (p 556)

Variety of changes can bee seen in meiotic or polytene chromosomes:

    deletions: show loop in meiotic chromosome (cri du chat in humans, del tip of chromo 5) (p 526)

    duplication can be tandem, or reverse also forms loop, but with same banding pattern as adjacent (p 530)

    inversion, depending on where centromere is, forms several kinds of loops:

                          paracentric      (centromere not in loop: can tie centromeres together in meiosis, breakage, and lost acentric fragments, 4 dif products (p 533-535)

                          pericentric:      crossovers produce four different products, each with centromere (p 534)

    translocation: form big X in synapsis from two chromosomes (p 537)

CHANGES IN NUMBER: p. 556:

euploid: multiples of haploid, polyploid, monoploid, diploid, triploid etc

    colchicine (isolated from autumn crocus) inhibits formation of mitotic spindle

Form polyploid plants, also double haploid to make diploid (p 557)

monoploid              plants derived fr anther tissue, used to generate new genotypes, 2x to become fertile

autopolyploid:        multiple sets of chromosomes from same species

allopolyploid:         different chromosomes from related plants

Aneuploid: extra of one or more chromosomes (SEE TABLE, P 570 in 7^th ed)

nondisjunction can produce trisomy at first or second meiotic division (p 566)

Trisomic:          2n + 1:

Trisomy 21:      Down's syndrome (see curve on p 569) 1/3rd die before 10, severely mentally retarded 1/700 all births, 1/2000 early years, 1/15 between 45-50, 1/7 over 49.

Sex Chromosome:         freq:                               signs: (MM, VX, p. 2148-2150)

Turner's                  XO     p 567             1/3000  pathognomic: lymphedema of dorsal hands&feet, neck, sterile, normal IQ

triple X                  XXX                         1/1000  little effect some times, may be sterile, may be retarded ('superfemale')

Klinefelter's           XXY  p 568             1/700    tall, eunuchoid, sterile, a few are retarded

super male             XYY                         1/1000               usually fertile, tall, severe acne, language dysfunction (1/15 [1:50?] in prisons for violent crimes)