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Changes in chromosome number:
1. - sets of chromosomes
2. - gain or loss of individual chromosomes
3. - examples of aneuploidy in humans
1.
Chapter 8
Human
Karyotypes and
Chromosome
Behavior
Changes in
chromosome
number
Jones and Bartlett Publishers © 2005
2.
Topics for today’s lecture
• Changes in chromosome number
- sets of chromosomes
- gain or loss of individual chromosomes
- examples of aneuploidy in humans
3.
Two kinds of polyploidy
Multiplication of the entire chromosome complement is called
polyploidy. When all the genomes are the same, it is called
autopolyploidy. When two (or more) different genomes
are duplicated, it is called allopolyploidy.
4.
Formation of a tetraploid organism
5.
Creation of a totally homozygous diploid cell by
doubling of chromosome number in a
monoploid cell by colchicine
Monoploid cells
can only be
grown in plants.
In humans, the
only viable
monoploid cells
are the egg and
the sperm.
Monoploidy in
somatic cells is
lethal.
6.
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.
7.
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
8.
Common
mechanisms by
which polyploids are
naturally produced
9.
Colchicine can be
used to block
segregation of
chromosomes at
anaphase results
in production of
polyploids.
10.
Where does chromosome doubling occur?
Chromosome doubling during meiosis Diploid
gametes
11.
Types of polyploids
• Autopolyploids = individuals with extra
copies of the monoploid set of chromosomes.
• Allopolyploids = result from combinations
of monoploid sets from several species.
12.
Sedum suaveolens, 2n=640, x=8
13.
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.
14.
diploid prg KY31 tf (6x)
Med tf +
diploid
Med. tf (6x) contam.
15.
Tall fescue, 2n=6x=42 (above left) Meadow fescue, 2n=2x=14 (above right)
Wide hybrid, 2n=8x=56 (below left) Wide hybrid, 2n=12x=84 (below right)
16.
Genomic in situ hybridization
17.
Where does chromosome doubling occur?
Chromosome doubling in meristematic tissue
autotetraploid clone.
18.
Production of new species of Brassica
These are
naturally
occuring species
of Brassica
produced by all
possible
combinations of
hybridizations
and
polyploidization
19.
Gamete production by polyploids
20.
Problems with
being triploid
failure of
chromosomes to
segregate
properly.
This is why
triploid
watermelons are
seedless.
21.
Origins
of a fertile
tetraploid by
hybridization
between 2
diploid species
= Allotetraploid
22.
Bread wheat
An
allopolyploid
with two
sequential
events
23.
Production of
New World
cotton by
hybridization of
two species
24.
Tetraploids can
make 6 kinds of
gametes
Tetrasomic
inheritance
results in many
more gamete and
zygote
combinations.
25.
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).
26.
Aneuploidy
• 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 = ?
27.
Datura
stramonium
Capsule
phenotypes for
normal + 12
aneuploids
(in this case, a
trisomic series).
28.
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
30.
Sex chromosome aneuploidy in humans
Syndrome Name Sex Chromosomes Frequency
Turner XO 1/2500 f
Normal females XX
Triplo-X XXX, XXXX, XXXX1/700 b
Nullo-X Y lethal
Normal males XY
Male XYY 1/1000 m
Klinefelter XXY, XXXY, XXXXY 1/500 m
31.
Kleinfelter’s Syndrome
Karyotype XXY
32.
Conserved linkages (synteny groups) in
cereal grasses
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