copyright © 2009 pearson education, inc. chapter 8 chromosome mutations: variation in chromosome...

Copyright © 2009 Pearson Education, Inc.

Chapter 8Chromosome Mutations: Variation in Chromosome Number and Arrangement


Copyright © 2009 Pearson Education, Inc. Figure 8.1

Non-Disjunction


Monosomy

• Results from the loss of one chromosome

• 2n – 1

• Loss of a chromosome in mammals is not tolerated

• Why do organisms not survive?


Trisomy

• Results from the gain of one chromosome

• 2n + 1

• In many cases, the individual can survive

• Trisomy is common in plants

• Jimson Weed


The 12 Possible Trisomies in Jimson Weed


Trisomies in Humans

• Down Syndrome (47, 21+)

• Patau Syndrome (47, 13+)

• Edwards Syndrome (47, 18+)


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


Down Syndrome


Patau Syndrome• Aka Trisomy 13

• 1 in 19,000 live births

• Average survival is 3 months

• Average age of parents is around 32


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


Aneuploidy Statistics

• David Carr

• 1971 study of spontaneously aborted fetuses

• Significant number were because of trisomies

• Monosomies were rarer

• Additional findings


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


Polyploidy


Autopolyploidy

• Can arise in several ways

• Autotriploids

• Autotetraploids

• Can be induced in the lab by adding colchicine to dividing cells

• Important to agriculture


Colchicine Induction


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


Endopolyploidy

• Condition in which only some cells are polyploid in an otherwise diploid organism


Variation in Internal Composition and Arrangement

of Chromosomes• Deletions

• Duplications

• Inverstions

• Translocations


Deletions

• A missing region of the chromosome


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


Duplications are important in evolution

• Mutations generally can’t happen in genes critical to survival

• Why?

• How could gene duplication allow this to happen?


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


No Crossing Over


Familial Down

Syndrome


Fragile Sites

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