1. Ch 8: Chromosome Mutations
Wheeler High School The Center for Advanced Studies in Science, Math & Technology
Fragile X
Ch 8: Chromosome Mutations
Post-AP DNA/Genetics – Ms. Kelavkar

2. Variations in Chromosome Number
Diploid species normally contain precisely two haploid chromosome sets, there are many known variations: a change in the total number of chromosomes, the deletion or duplication of genes or segments of a chromosome, and rearrangements of the genetic material either within or among chromosomes.
Duplication Event
Post-AP DNA/Genetics – Ms. elavkar

3. Aneuploidy (abnormal # of chromosomes)
Variations in chromosome number are known as aneuploidy. This term describes when an organism has gained or lost one or more chromosomes but NOT a complete set.
Trisomy & Monosomy as two examples of aneuploidy.
Post-AP DNA/Genetics – Ms. Kelavkar

4. Euploidy & Polyploidy
In euploidy, complete haploid sets of chromosomes are present.
Polyploidy occurs when more than two sets of chromosomes are present.
Euploidy
Polyploid
Post-AP DNA/Genetics – Ms. elavkar

5. Table 8-1 Copyright © 2006 Pearson Prentice Hall, Inc.
Table 8.1 Terminology for Variation in Chromosome Numbers
Table Copyright © 2006 Pearson Prentice Hall, Inc.

6. Nondisjunction
This is when chromosomes or chromatids fail to disjoin and move to opposite poles during meiosis I or II.
Post-AP DNA/Genetics – Ms. Kelavkar

8. Figure 8-1 Copyright © 2006 Pearson Prentice Hall, Inc.
Figure 8-1 Nondisjunction during the first and second meiotic divisions. In both cases, some of the gametes formed either contain two members of a specific chromosome or lack that chromosome. Following fertilization by a gamete with a normal haploid content, monosomic, disomic (normal), or trisomic zygotes are produced.
Figure Copyright © 2006 Pearson Prentice Hall, Inc.

9. Monosomy
Monosomy: the Loss of a Single Chromosome, May Have Severe Phenotypic Effects
Partial Monosomy in Humans: The Cri-du-Chat Syndrome (missing part of C5)
Post-AP DNA/Genetics – Ms. Kelavkar

10. Figure 8-2 Copyright © 2006 Pearson Prentice Hall, Inc.
A representative karyotype and photograph of a child exhibiting cri-du-chat syndrome. In the karyotype, the arrow identifies the absence of a small part of the short arm of one member of the chromosome 5 homologs.
Figure 8-2 A representative karyotype and photograph of a child exhibiting cri-du-chat syndrome (46,5p). In the karyotype, the arrow identifies the absence of a small part of the short arm of one member of the chromosome 5 homologs.
Figure Copyright © 2006 Pearson Prentice Hall, Inc.

11. Total Monosomy
Although monosomy for the X chromosome occurs in humans, monosomy for any of the autosomes is usually not tolerated in humans and other animals.
However, partial monosomy (segmental deletion) only a section of a chromosome is lost and is generally tolerated and non-lethal.
Post-AP DNA/Genetics – Ms. Kelavkar

12. Trisomy
Trisomy Involves the Addition of a Chromosome to a Diploid Genome
The karyotype and a photograph of a child with Down syndrome. In the karyotype, three members of the G-group chromosome 21 are present, creating the 47, condition.

13. Figure 8-6 Copyright © 2006 Pearson Prentice Hall, Inc.
Figure 8-6 Incidence of Down syndrome births contrasted with maternal age.
Figure Copyright © 2006 Pearson Prentice Hall, Inc.

14. Figure 8-7 Copyright © 2006 Pearson Prentice Hall, Inc.
Trisomy
The karyotype and potential phenotypic characteristics associated with Patau syndrome, where three members of the D group chromosome 13 are present, creating the 47, condition.
AKA: Trisomy 13
Figure 8-7 The karyotype and potential phenotypic characteristics associated with Patau syndrome, where three members of the D group chromosome 13 are present, creating the 47, condition.
Figure Copyright © 2006 Pearson Prentice Hall, Inc.

15. Figure 8-8 Copyright © 2006 Pearson Prentice Hall, Inc.
Trisomy
The karyotype and potential phenotypic characteristics associated with Edwards syndrome. Three members of the E group chromosome 18 are present, creating the 47, condition.
Figure 8-8 The karyotype and potential phenotypic characteristics associated with Edwards syndrome. Three members of the E group chromosome 18 are present, creating the 47, condition.
Figure Copyright © 2006 Pearson Prentice Hall, Inc.

16. Trisomies vs. Monosomies
Trisomies are often found in spontaneously aborted fetuses, but monosomies are not, which suggests that monosomic gametes may be very functionally impaired

17. Any Questions?

18. Wheeler High School The Center for Advanced Studies in Science, Math & Technology
Ch 8: Genetic Mutations
Post-AP DNA/Genetics – Ms. Kelavkar

19. Polyploidy
Recall from last class; polyploidy describes instances in which more than 2 haploid chromosome sets are found.
The naming of polyploids is based on the number of sets of chromosomes found: a triploid has 3n chromosomes; a tetraploid has 4n; a pentaploid, 5n; and so forth

20. How Does Polyploidy Occur
Two Ways:
Autopolyploidy – addition of one or more extra sets of chromosomes (same species)
Allopolyploidy – hybridization (different species)

21. Autopolyploidy and Allopolyploidy
Polyploidy can originate by the addition of one or more sets of chromosomes identical to the haploid complement of the same species (autopolyploidy) or by the combination of chromosome sets from different species as a consequence of interspecific matings (allopolyploidy)

22. Allotetraploid
An allotetraploid arises from hybridization of two closely related species.

23. Figure 8-11 Copyright © 2006 Pearson Prentice Hall, Inc.
The origin and propagation of an amphidiploid. Species 1 contains genome A consisting of three distinct chromosomes, and Species 2 contains genome B consisting of two distinct chromosomes, and Following fertilization between members of the two species and chromosome doubling, a fertile amphidiploid containing two complete diploid genomes (AABB) is formed.
Figure 8-11 The origin and propagation of an amphidiploid. Species 1 contains genome A consisting of three distinct chromosomes, and Species 2 contains genome B consisting of two distinct chromosomes, and Following fertilization between members of the two species and chromosome doubling, a fertile amphidiploid containing two complete diploid genomes (AABB) is formed.
Figure Copyright © 2006 Pearson Prentice Hall, Inc.

24. Amphidiploid plants can be produced by somatic cell hybridization.
Figure 8-13 Application of the somatic cell hybridization technique in the production of an amphidiploid. Cells from the leaves of two species of plants are removed and cultured. The cell walls are digested away and the resultant protoplasts are induced to undergo cell fusion. The hybrid cell is selected and stimulated to divide and differentiate, as illustrated in the photograph. An amphidiploid has a complete set of chromosomes from each parental cell type and displays phenotypic characteristics of each. Two pairs of chromosomes from each species are depicted.
Figure Copyright © 2006 Pearson Prentice Hall, Inc.

25. Variation Occurs in the Structure and Arrangement of Chromosomes
Rearrangements of chromosome segments include deletions, duplications, inversions, nonreciprocal translocations, and reciprocal translocations.

26. Figure 8-14 Copyright © 2006 Pearson Prentice Hall, Inc.
Figure 8-14 Overview of the five different types of rearrangement of chromosome segments.
Figure Copyright © 2006 Pearson Prentice Hall, Inc.

27. Figure 8-14a Copyright © 2006 Pearson Prentice Hall, Inc.
Figure 8-14a Overview of the five different types of rearrangement of chromosome segments.
Figure 8-14a Copyright © 2006 Pearson Prentice Hall, Inc.

28. Figure 8-14b Copyright © 2006 Pearson Prentice Hall, Inc.
Figure 8-14b Overview of the five different types of rearrangement of chromosome segments.
Figure 8-14b Copyright © 2006 Pearson Prentice Hall, Inc.

29. Figure 8-14c Copyright © 2006 Pearson Prentice Hall, Inc.
Figure 8-14c Overview of the five different types of rearrangement of chromosome segments.
Figure 8-14c Copyright © 2006 Pearson Prentice Hall, Inc.

30. Figure 8-14d Copyright © 2006 Pearson Prentice Hall, Inc.
Figure 8-14d Overview of the five different types of rearrangement of chromosome segments.
Figure 8-14d Copyright © 2006 Pearson Prentice Hall, Inc.

31. Figure 8-14e Copyright © 2006 Pearson Prentice Hall, Inc.
Figure 8-14e Overview of the five different types of rearrangement of chromosome segments.
Figure 8-14e Copyright © 2006 Pearson Prentice Hall, Inc.

32. 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)

33. Figure 8-15 Copyright © 2006 Pearson Prentice Hall, Inc.
Terminal deletion
Interclay Deletion
Pairing occurs between a normal chromosome and one with an interclay deletion by looping out the undeleted portion to form a deletion (compensation) loop.
Figure 8-15 Origins of (a) a terminal and (b) intercalary deletion. In part (c), pairing occurs between a normal chromosome and one with an intercalary deletion by looping out the undeleted portion to form a deletion (or a compensation) loop.
Figure Copyright © 2006 Pearson Prentice Hall, Inc.

34. Duplication Events
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.
Evolution anyone?

35. Figure 8-17 Copyright © 2006 Pearson Prentice Hall, Inc.
The origin of duplicated and deficient regions of chromosomes as a result of unequal crossing over. The tetrad at the left is mispaired during synapsis. A single crossover between chromatids 2 and 3 results in deficient and duplicated chromosomal regions. (See chromosomes 2 and 3, respectively, on the right.) The two chromosomes uninvolved in the crossover event remain normal in their gene sequence and content.
Figure 8-17 The origin of duplicated and deficient regions of chromosomes as a result of unequal crossing over. The tetrad at the left is mispaired during synapsis. A single crossover between chromatids 2 and 3 results in deficient and duplicated chromosomal regions. (See chromosomes 2 and 3, respectively, on the right.) The two chromosomes uninvolved in the crossover event remain normal in their gene sequence and content.
Figure Copyright © 2006 Pearson Prentice Hall, Inc.

36. Inversions
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.
An inversion may arise from chromosomal looping.

37. Figure 8-19 Copyright © 2006 Pearson Prentice Hall, Inc.
Figure 8-19 One possible origin of a pericentric inversion.
Figure Copyright © 2006 Pearson Prentice Hall, Inc.

38. Paracentric and Pericentric Inversions
A paracentric inversion does not change the relative lengths of the two arms of a chromosome, whereas a pericentric inversion does.

39. Figure 8-20 A comparison of the arm ratios of a submetacentric chromosome before and after the occurrence of a paracentric and pericentric inversion. Only the pericentric inversion results in an alteration of the original ratio.
A comparison of the arm ratios of a submetacentric chromosome before and after the occurrence of a paracentric and pericentric inversion. Only the pericentric inversion results in an alteration of the original ratio.

40. Any Questions?