copyright © 2009 pearson education, inc. chapter 8 chromosome mutations: variation in chromosome...
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Copyright © 2009 Pearson Education, Inc.
Chapter 8Chromosome Mutations: Variation in Chromosome Number and Arrangement
Copyright © 2009 Pearson Education, Inc.
Copyright © 2009 Pearson Education, Inc. Table 8.1
Copyright © 2009 Pearson Education, Inc. Figure 8.1
Non-Disjunction
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Monosomy
• Results from the loss of one chromosome
• 2n – 1
• Loss of a chromosome in mammals is not tolerated
• Why do organisms not survive?
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Trisomy
• Results from the gain of one chromosome
• 2n + 1
• In many cases, the individual can survive
• Trisomy is common in plants
• Jimson Weed
Copyright © 2009 Pearson Education, Inc. Figure 8.2
The 12 Possible Trisomies in Jimson Weed
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Trisomies in Humans
• Down Syndrome (47, 21+)
• Patau Syndrome (47, 13+)
• Edwards Syndrome (47, 18+)
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Down Syndrome
• First reported in 1866
• 1 in 800 live births
• Physical, physiological, and mental abnormalities
• Average life expectancy is around 50 years
• Can arise through non-disjunction in anaphase I or II
• 75% are during meiosis I
• 95% are from errors in ovum formation
Copyright © 2009 Pearson Education, Inc. Figure 8.4
Down Syndrome
Copyright © 2009 Pearson Education, Inc. Figure 8.5
Copyright © 2009 Pearson Education, Inc. Figure 8.6
Patau Syndrome• Aka Trisomy 13
• 1 in 19,000 live births
• Average survival is 3 months
• Average age of parents is around 32
Copyright © 2009 Pearson Education, Inc. Figure 8.7
Edwards Syndrome
• Aka Trisomy 18
• 1 in 8,000 live births
• Average survival is 4 months
• Average maternal age is 34.7
• Most infants are females
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Aneuploidy Statistics
• David Carr
• 1971 study of spontaneously aborted fetuses
• Significant number were because of trisomies
• Monosomies were rarer
• Additional findings
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Polyploidy
• Occurs when there are more than 2 haploid sets of chromosomes
• Naming is based on the number of sets
• Triploidy – 3n
• Tetraploid – 4n
• Common in plants, not so common in animals
• Autopolyploidy vs. Allopolyploidy
Copyright © 2009 Pearson Education, Inc. Figure 8.8
Polyploidy
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Autopolyploidy
• Can arise in several ways
• Autotriploids
• Autotetraploids
• Can be induced in the lab by adding colchicine to dividing cells
• Important to agriculture
Copyright © 2009 Pearson Education, Inc. Figure 8.9
Colchicine Induction
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Allopolyploidy
• Results from hybridizing two closely related species
• Usually can’t reproduce because can’t produce viable gametes
• Can be induced in the lab using cochicine
Copyright © 2009 Pearson Education, Inc. Figure 8.10
Copyright © 2009 Pearson Education, Inc. Figure 8.11
Copyright © 2009 Pearson Education, Inc.
Endopolyploidy
• Condition in which only some cells are polyploid in an otherwise diploid organism
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Variation in Internal Composition and Arrangement
of Chromosomes• Deletions
• Duplications
• Inverstions
• Translocations
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Deletions
• A missing region of the chromosome
Copyright © 2009 Pearson Education, Inc. Figure 8.13a
Deletions
• A missing region of a chromosome
• Terminal deletion
• Intercalary deletion
Copyright © 2009 Pearson Education, Inc. Figure 8.14
Copyright © 2009 Pearson Education, Inc. Figure 8.15
Cri du Chat Syndrome
Copyright © 2009 Pearson Education, Inc. Figure 8.13b
Duplications
• The presence of any part of the genetic material more than once in a genome
• Results from misalignment during synapse
• Three interesting aspects of duplications
• Result in gene redundancy
• May produce phenotypic variation
• Important for evolution
Copyright © 2009 Pearson Education, Inc. Figure 8.17
Copyright © 2009 Pearson Education, Inc. Figure 8.13b
Duplications are important in evolution
• Mutations generally can’t happen in genes critical to survival
• Why?
• How could gene duplication allow this to happen?
Copyright © 2009 Pearson Education, Inc. Figure 8.13b
Inversions
• Occurs when the genetic information within a chromosome gets flipped
• No loss or gain, just rearrangement
• Paracentric vs Pericentric
• The individual is usually not affected
• But might have problems producing gametes
Copyright © 2009 Pearson Education, Inc. Figure 8.19
Copyright © 2009 Pearson Education, Inc. Figure 8.20
Copyright © 2009 Pearson Education, Inc. Figure 8.21
No Crossing Over
Copyright © 2009 Pearson Education, Inc. Figure 8.22
Copyright © 2009 Pearson Education, Inc. Figure 8.13d
Translocations
Copyright © 2009 Pearson Education, Inc. Figure 8.25
Familial Down
Syndrome
Copyright © 2009 Pearson Education, Inc. Figure 8.26
Fragile Sites
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