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Concepts of Genetics
Ninth Edition
Klug, Cummings, Spencer, Palladino
Chapter 8
Chromosome Mutations: Variation in
Chromosome Number and Arrangement
Lectures by David Kass with contributions from
John C. Osterman.
Copyright
© 2009©Pearson
Education,
Inc.
Copyright
2009 Pearson
Education,
Inc.
8.1 Specific Terminology Describes
Variations in Chromosome Number
•
•
Aneuploidy
Euploidy
•
Polyploidy
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Nondisjunction
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Figure 8.1
8.2 Monosomy, the Loss of a Single
Chromosome, May Have Severe
Phenotypic Effects
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Section 8.3
• 8.3Trisomy Involves the Addition of a
Chromosome to a Diploid Genome
• Trisomy (2n + 1 chromosomes) for the
sex chromosomes has a less dramatic
phenotype than trisomies for autosomes,
which are often lethal.
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Jimson weed:
Datura
stramonium
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Figure 8.2
Section 8.3
• Down syndrome results from trisomy of
chromosome 21. (Figure 8.4)
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Mouse Model
• Is trisomic for Down Syndrome Critical
Region (DSCR)
Science Daily. 2009. Retrieved on 10/14/2013
http://www.sciencedaily.com/releases/2009/11/091118143207.htm
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Copyright © 2009 Pearson Education, Inc.
Figure 8.5
Patau
Syndrome
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Figure 8.6
Edwards
Syndrome
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Figure 8.7
Section 8.3
• Trisomies are often found in
spontaneously aborted fetuses, but
monosomies are not.
• This suggests that monosomic gametes
may be functionally impaired.
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Section 8.4
• 8.4Polyploidy, in Which More Than Two
Haploid Sets of Chromosomes Are
Present, Is Prevalent in Plants
• The naming of polyploids is based on the
number of sets of chromosomes found:
•
•
•
•
a triploid has 3n chromosomes
a tetraploid has 4n chromosomes
a pentaploid, 5n chromosomes
and so forth
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Section 8.4
• Polyploidy can originate by:
• the addition of one or more sets of
chromosomes identical to the haploid
complement of the same species
(autopolyploidy)
• or the combination of chromosome sets from
different species as a consequence of
interspecific matings (allopolyploidy) (Figure
8.8)
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Copyright © 2009 Pearson Education, Inc.
Figure 8.8
Autopolyploidy
• In plants, more than the diploid number
often produce larger cells and, thus,
larger plants
• This is desirable for commercial value.
• e.g. Some types of: commercial bananas
(triploid), seedless watermelons, coffee
(tetraploid), peanuts (tetraploid), McIntosh
apples (tetraploid), strawberry (octoploid)
• May treat with colchicine to get balanced
gametes
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Allopolyploidy
• Can the hybrid produce viable
gametes?
• Is there chromosomal balance?
• If not it is doomed to never reproduce.
• If yes, then likely will produce viable
gametes.
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Cultivated Species-American Cotton Gossypium
• Amphidiploid-hybrid derived from 2
species of known origin
• 26 pairs of chromosomes (13 larger
chromosomes and 13 smaller chromosomes)
• Contains chromosomes from Old World
strain and the wild American strain
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Section 8.5
• 8.5Variation Occurs in the Internal
Composition and Arrangement of
Chromosomes
• Rearrangements of chromosome
segments include:
•
•
•
•
•
deletions
duplications
inversions
nonreciprocal translocations
reciprocal translocations (Figure 8.13)
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Copyright © 2009 Pearson Education, Inc.
Figure 8.13
8.6 A Deletion Is a Missing Region
of a Chromosome
• When a chromosome breaks in one or
more places and a portion of it is lost, the
missing piece is referred to as a deletion
(or a deficiency).
• The deletion can occur:
• near one end (terminal deletion)
• or from the interior of the chromosome
(intercalary deletion) (Figure 8.14)
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Figure 8.14
Section 8.6
• Cri-du-chat results from a segmental
deletion of a small terminal portion of the
short arm of chromosome 5 (Figure 8.15).
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Section 8.6
• The type of Notch phenotypic expression
of recessive genes in association with a
deletion in Drosophila is an example of
pseudodominance.
http://www.cdb.riken.go.jp/en/04_news/articles/img/041229_01.jpg
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8.7 A Duplication Is a Repeated Segment of
the Genetic Material
• Duplications arise as the result of unequal
crossing over during meiosis or through a
replication error prior to meiosis (Figure
8.17).
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Example of Gene Redundancy
• Organisms have multiple copies of the
ribosomal RNA genes (rDNA).
• This is an example of gene redundancy.
• Gene amplification is another
mechanism to increase the rRNA.
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The Bar-eye phenotype in Drosophila
results from duplication (Figure 8.18).
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Section 8.8
• 8.8Inversions Rearrange the Linear Gene
Sequence
• An inversion involves a rearrangement of
the linear gene sequence rather than the
loss of genetic information.
• In an inversion, a segment of a
chromosome is turned around 180° within
a chromosome.
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Copyright © 2009 Pearson Education, Inc.
Figure 8.19
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Figure 8.20
Section 8.8
• Synapsis of inverted chromosomes
requires an inversion loop (Figure 8.21).
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Section 8.8
• Figure 8.22 shows the effects of a single
crossover within an inversion loop for both
paracentric and pericentric inversion
heterozygotes.
• For a paracentric inversion crossover:
• one recombinant chromatid is dicentric (two
centromeres)
• one is acentric (lacking a centromere)
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Copyright © 2009 Pearson Education, Inc.
Figure 8.22
8.9 Translocations Alter the Location
of Chromosomal Segments in the
Genome
• Translocation - movement of a
chromosomal segment to a new location in
the genome.
• Reciprocal Translocation:
• involves exchange of segments between 2
nonhomologous chromosomes
• has an unusual synapsis configuration during
meiosis
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Figure 8.23
Section 8.9
• Robertsonian
translocation or
centric fusion
involves breaks at
the extreme ends of
the short arms of 2
nonhomologous
acrocentric
chromosomes
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Familial Down
Syndrome
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Figure 8.25
Section 8.10
• 8.10
Fragile Sites in Humans Are
Susceptible to Chromosome Breakage
• Fragile sites are more susceptible to
chromosome breakage when cells are
cultured in the absence of certain
chemicals such as folic acid.
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Section 8.10
• Fragile X
syndrome (Martin–
Bell syndrome) is
the most common
form of inherited
mental retardation,
affecting about 1 in
4000 males and 1 in
8000 females, and
is a dominant trait
(Figure 8.26).
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Boys with fragile X syndrome
(Reprinted from Medical Genetics,
2nd ed., Jorde LB, et al, ©2000)
The End
Hinny – cross between male
horse and female donkey
Mule – cross between female
horse and male donkey
http://www.greenpacks.org/wp-content/uploads/2008/10/hinny.jpg
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_20070726_A1_CD26MULE~p1.JPG
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