Types of Chromosome Aberrations or abnormalities.pptx

Basic Info about the topic

1. Chromosome Aberrations

2. Two major processes are responsible for genetic variation, mutation and recombination . The term mutation covers a broad array of different kinds of changes. we focus on mutational events that take place within individual genes. We call such events gene mutations .

3. Types of Genetic variation Allelic variations mutations in particular genes (loci) Chromosomal aberrations substantial changes in chromosome structure Typically affect multiple genes (loci) 8-2 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display

4. Categories of Chromosomal Aberrations Aneuploidies A change from euploid number Deletions Loss of a region of a chromosome Duplications Translocations Exchange or joining of regions of two non-homologous chromosomes Inversions Pericentric – inversion about the centromere Paracentric – inversion not involving the centromere

5. Variation In Chromosome Number Euploidy Normal variations of the number of complete sets of chromosomes Haploid, Diploid, Triploid, Tetraploid , etc… Aneuploidy Variation in the number of particular chromosomes within a set Monosomy , trisomy , polysomy

6. Aneuploidies of the Sex Chromosomes 47, XXY 45, X Klinefelter syndrome Turner syndrome

7. Trisomy 13 Karyotype : 47, 13+

8. Karyotype of t(14;21) Familial Down Syndrome

9. Polyploidy v Aneuploidy

10. Meiotic Nondisjunction Generates Aneuploidies abnormal gametes Zygotic Ploidy Zygotic Ploidy

11. Plants commonly exhibit polyploidy 30-35% of ferns and flowering plants are polyploid Many of the fruits & grain are polyploid plants Polyploid strains often display desirable agricultural characteristics wheat cotton strawberries bananas large blossom flowers Euploidy Variations

12. Generation of Polyploids Autopolyploidy Complete nondisjunction of both gametes can produce an individual with one or more sets of chromosomes Figure 8.27

13. Interspecies Crosses can Generate Alloploids Alloploidy Offspring generally sterile Figure 8.27

14. Figure 8.27 An allotetraploid : Contains two complete sets of chromosomes from two different species Interspecies Crosses Result in Alloploids Allodiploid one set of chromosomes from two different species Allopolyploid combination of both autopolyploidy and alloploidy

15. Amount of genetic information in the chromosome can change Deficiencies/Deletions Duplications The genetic material remains the same, but is rearranged Inversions Translocations Variation In Chromosome Structure

16. A chromosomal deficiency occurs when a chromosome breaks and a fragment is lost Deficiencies (aka Deletions)

17. Phenotypic consequences of deficiency depends on Size of the deletion Functions of the genes deleted Phenotypic effect of deletions usually detrimental Deficiencies

18. Cri-du-chat Syndrome (Partial Monosomy in Humans)

19. Cri-du-chat (cat's cry) syndrome, also known as 5p- syndrome, is a chromosomal condition that results when a piece of  chromosome 5  is missing. Infants with this condition often have a high-pitched cry that sounds like that of a cat. The disorder is characterized by intellectual disability and delayed development, small head size ( microcephaly ), low birth weight, and weak muscle tone ( hypotonia ) in infancy. Affected individuals also have distinctive facial features, including widely set eyes ( hypertelorism ), low-set ears, a small jaw, and a rounded face. Some children with cri-du-chat syndrome are born with a heart defect

20. A chromosomal duplication is usually caused by abnormal events during recombination Duplications Figure 8.5

21. Phenotypic consequences of duplications correlated to size & genes involved Duplications tend to be less detrimental Duplications

22. Majority of small duplications have no phenotypic effect However, they provide raw material for evolutionary change Lead to the formation of gene families A gene family consists of two or more genes that are similar to each other derived from a common gene ancestor Duplications and Gene Families

23. Genes derived from a single ancestral gene Duplications Generate Gene Families

24. Gene Families Well-studied example is the globin gene family Genes encode proteins that bind oxygen Globin gene family 14 homologous genes derived from a single ancestral gene Accumulation of mutations in the members of generated Globin genes expressed during different stages of development Globin proteins specialized in their function

25. A segment of chromosome that is flipped relative to that in the homologue Inversions Figure 8.11 Centromere lies within inverted region Centromere lies outside inverted region

26. Inversions No loss of genetic information Many inversions have no phenotypic consequences Break point effect Inversion break point is within regulatory or structural portion of a gene Position effect Gene is repositioned in a way that alters its gene expression separated from regulatory sequences, placed next to constitutive heterochromatin ~ 2% of the human population carries karyotypically detectable inversions

27. When a segment of one chromosome becomes attached to another In reciprocal translocations two non-homologous chromosomes exchange genetic material Usually generate so-called balanced translocations Usually without phenotypic consequences Although can result in position effect Translocations

28. Fig. 8.13b(TE Art) Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Nonhomologous chromosomes Reciprocal translocation 1 1 7 7 Nonhomologous crossover 1 7 Crossover between nonhomologous chromosomes

29. Fig. 8.13a(TE Art) Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 22 Environmental agent causes 2 chromosomes to break. Reactive ends 22 2 2 DNA repair enzymes recognize broken ends and connect them. Chromosomal breakage and DNA repair

30. Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display In simple translocations the transfer of genetic material occurs in only one direction These are also called unbalanced translocations Unbalanced translocations are associated with phenotypic abnormalities or even lethality Example: Familial Down Syndrome In this condition, the majority of chromosome 21 is attached to chromosome 14 (Figure 8.14 a )