Two kinds of polyploidy
Creation of a totally homozygous diploid cell by doubling of chromosome number in a monoploid cell by colchicine
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. 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 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 Male XYY 1/1000 m Klinefelter XXY, XXXY, XXXXY 1/500 m
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