Copyright © 2009 Pearson Education, Inc. PowerPoint ® Lecture Presentation for 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.
8.1Specific Terminology Describes Variations in Chromosome Number Aneuploidy Euploidy Polyploidy
Copyright © 2009 Pearson Education, Inc. Figure 8.1 Nondisjunction
Copyright © 2009 Pearson Education, Inc. 8.2Monosomy, the Loss of a Single Chromosome, May Have Severe Phenotypic Effects
Copyright © 2009 Pearson Education, Inc. 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. Section 8.3
Copyright © 2009 Pearson Education, Inc. Figure 8.2 Jimson weed: Datura stramonium
Copyright © 2009 Pearson Education, Inc. Down syndrome results from trisomy of chromosome 21. (Figure 8.4) Section 8.3
Copyright © 2009 Pearson Education, Inc. Mouse Model Is trisomic for Down Syndrome Critical Region (DSCR) Science Daily Retrieved on 10/14/2013
Copyright © 2009 Pearson Education, Inc. Figure 8.5
Copyright © 2009 Pearson Education, Inc. Figure 8.6 Patau Syndrome
Copyright © 2009 Pearson Education, Inc. Figure 8.7 Edwards Syndrome
Copyright © 2009 Pearson Education, Inc. Trisomies are often found in spontaneously aborted fetuses, but monosomies are not. This suggests that monosomic gametes may be functionally impaired. Section 8.3
Copyright © 2009 Pearson Education, Inc. 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 Section 8.4
Copyright © 2009 Pearson Education, Inc. 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) Section 8.4
Copyright © 2009 Pearson Education, Inc. Figure 8.8
Copyright © 2009 Pearson Education, Inc. 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
Copyright © 2009 Pearson Education, Inc. 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.
Copyright © 2009 Pearson Education, Inc. 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
Copyright © 2009 Pearson Education, Inc. 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) Section 8.5
Copyright © 2009 Pearson Education, Inc. Figure 8.13
Copyright © 2009 Pearson Education, Inc. 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) 8.6A Deletion Is a Missing Region of a Chromosome
Copyright © 2009 Pearson Education, Inc. Figure 8.14
Copyright © 2009 Pearson Education, Inc. Cri-du-chat results from a segmental deletion of a small terminal portion of the short arm of chromosome 5 (Figure 8.15). Section 8.6
Copyright © 2009 Pearson Education, Inc. The type of Notch phenotypic expression of recessive genes in association with a deletion in Drosophila is an example of pseudodominance. Section 8.6
Copyright © 2009 Pearson Education, Inc. Duplications arise as the result of unequal crossing over during meiosis or through a replication error prior to meiosis (Figure 8.17). 8.7A Duplication Is a Repeated Segment of the Genetic Material
Copyright © 2009 Pearson Education, Inc. 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. Example of Gene Redundancy
Copyright © 2009 Pearson Education, Inc. The Bar-eye phenotype in Drosophila results from duplication (Figure 8.18).
Copyright © 2009 Pearson Education, Inc. 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. Section 8.8
Copyright © 2009 Pearson Education, Inc. Figure 8.19
Copyright © 2009 Pearson Education, Inc. Figure 8.20
Copyright © 2009 Pearson Education, Inc. Synapsis of inverted chromosomes requires an inversion loop (Figure 8.21). Section 8.8
Copyright © 2009 Pearson Education, Inc. 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) Section 8.8
Copyright © 2009 Pearson Education, Inc. Figure 8.22
Copyright © 2009 Pearson Education, Inc. 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 8.9Translocations Alter the Location of Chromosomal Segments in the Genome
Copyright © 2009 Pearson Education, Inc. Figure 8.23
Copyright © 2009 Pearson Education, Inc. Robertsonian translocation or centric fusion involves breaks at the extreme ends of the short arms of 2 nonhomologous acrocentric chromosomes Section 8.9
Copyright © 2009 Pearson Education, Inc. Figure 8.25 Familial Down Syndrome
Copyright © 2009 Pearson Education, Inc. 8.10Fragile 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. Section 8.10
Copyright © 2009 Pearson Education, Inc. 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). Section 8.10 Boys with fragile X syndrome (Reprinted from Medical Genetics, 2nd ed., Jorde LB, et al, ©2000)
Copyright © 2009 Pearson Education, Inc. The End _ _A1_CD26MULE~p1.JPG Hinny – cross between male horse and female donkey Mule – cross between female horse and male donkey