Chapter 8 Human Karyotypes and Chromosome Behavior Changes in chromosome number



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Chapter 8 Human Karyotypes and Chromosome Behavior Changes in chromosome number




Two kinds of polyploidy





Creation of a totally homozygous diploid cell by doubling of chromosome number in a monoploid cell by colchicine



Terms for sets of chromosomes

  • Monoploid = basic, standard number of chromosomes that contain one copy of each gene found in the species.

  • The letter X is used to designate the monoploid set.

  • X = Humans-23, Drosophila-4, chicken-39, cattle-30, pigeon-40, tobacco-12, Arabidopsis-5, wheat-7 pea-7, oak-12.

  • Dysploid = a change in monoploid number.



Terms for sets of chromosomes

  • Euploid = one or more complete sets of chromosomes.

  • Polyploid = three or more complete sets:

  • haploid (N) set

  • diploid = 2X N = X

  • triploid = 3X

  • tetraploid = 4X N = 2X

  • pentaploid = 5X

  • hexaploid = 6X N = 3X

  • duodecaploid = 12X N = 6X









Types of polyploids

  • Autopolyploids = individuals with extra copies of the monoploid set of chromosomes.

  • Allopolyploids = result from combinations of monoploid sets from several species.



Sedum suaveolens, 2n=640, x=8



Flow cytometry

  • Ploidy determinations can be made using chromosome-specific fluorescent dyes and a cell sorter.

  • Results need to be confirmed by classical cytogenetics.

  • Efficient for screening for haploids, dihaploids, etc.

  • Amphiploid – doubled wide hybrid.

























Aneuploidy

  • Aneuploidy is a gain or loss of individual chromosomes.

  • Normal diploids are disomic.

  • Trisomic = diploid with one extra chromosome (2X+1).

  • Monosomic = loss of a single chromosome (2X-1).



Tetrasomic = two extra copies of one chromosome (2X + 2).

  • Tetrasomic = two extra copies of one chromosome (2X + 2).

  • Nullisomic = individuals that have lost both copies of a particular chromosome (2X-2)

  • Double monosomics = ?

  • Double trisomics = ?





Human aneuploidy

  • Humans, and animals in general, can’t tolerate much chromosome aberration.

  • In humans, aneuploids for X, Y, 13, 18 and 21 can survive to birth.

  • Trisomy 13 = Patau syndrome

  • Trisomy 18 = Edwards syndrome

  • Trisomy 21 = Down syndrome





Sex chromosome aneuploidy in humans

  • Syndrome Name Sex Chromosomes Frequency

  • Turner XO 1/2500 f

  • Normal females XX

  • Triplo-X XXX, XXXX, XXXX 1/700 b

  • Nullo-X Y lethal

  • Normal males XY

  • Male XYY 1/1000 m

  • Klinefelter XXY, XXXY, XXXXY 1/500 m







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