Structural Chromosome aberration ppt

Structural chromosome aberration

1. Elements of genetics TOPIC : STRUCTURAL CHROMOSOME Aberration NAME : UPAYAN SARKAR ERP ID : 0191BSC027 CLASS : BSC AGRICULTURE(2 nd sem ) SEC : A SUBMITTED TO: DR. HIMANKI DABRAL MAM

2. CONTENTS What is chromosome What is chromosome aberration Classification of chromosome aberration Types of structural chromosome aberration

3. Chromosome Chromosomes are rod shaped or thread like condensed chromatin fibres which store and transmit coded hereditary information. Chromosomes are a lot like these thread like structures , although a lot less flamboyant. They are located inside the nucleus of animal and plant cells. Each chromosome happens to made of proteins and a single molecule of deoxyribonucleic acid or commonly abbreviated to DNA. The structure of chromosome consist of: 1.Chromonema 2.Primary constriction or centromere 3.Secondary constriction 4.Telomere

4. Chromosome aberration Mutations that cause change in the structure or number of chromosomes are called chromosomal aberrations. Alteration in the structure of individual chro­mosome or chromosomal aberration may occur spontaneously or by induction. Such changes may result in quantitative alteration of genes or rearrangement of genes. The breakage and reunion of chromatid segments result in a number of abnormalities in the chromosome structure. Thus origin of structural changes is caused by breaks in the chromosome.

5. CLASSIFICATION OF CHROMOSOMAL ABERRATION : Structural Chromosomal Aberration : Change in the structure of chromosomes. Numerical Chromosomal Aberration: Change in the number of chromosomes

6. Structural chromosome aberration It results from chromosome breakage. Broken chromosomes tend to re-join; if there is more than one break, re-joining occurs randomly and not necessarily to the correct ends. Chromosome breakage is caused by X-rays, various chemicals, and can also occur spontaneously

7. Types of structural chromosomal aberration Common types of structural aberrations: 1. Deletion 2. Duplication 3. Inversion 4. Translocation 5. Ring chromosome 6. Insertion

8. deletion “Loss of a (generally small) segment of chromosome” Spontaneously or may be induced (radiation, UV, chemicals, viruses). Detection is based on unpaired region of normal chromosome that produces a loop during pachytene stage. Firstly observed by Bridges in 1917 in Drosophila. An event in which a piece of chromosome is missing or deleted. Can remove one or more genes from chromosome. Deletion may be terminal or intercalary.

9. deletion Terminal deletion : “Loss of either terminal segment of a chromosome” In 1938, Muller postulated that loss of telomere makes chromosome unstable so it is not commonly observed. Occurs towards the end of the chromosome. May cause abnormal skull structure, mental retardation, and growth delay E.g. Maize

10. deletion Intercalary deletion – “Loss of segment in between centromere and telomere” It is commonly observed in drosophila occurs from the interior of a chromosome. May cause broad forehead, small chin, prominent eyes, and downturned mouth.

11. deletion Effects of deletion: Crossing over not occur. Harmful effect on diploid organisms. Morphological effects. A B C D E F G A B D E F G C

12. Figure of deletion

13. DUPLICATION “Occurrence of a segment twice in the same chromosomes” Given by Bridges in 1919. Occurs due to unequal crossing over or crossing over in inversion or translocated heterozygotes. It is detected by presence of loop in duplicated region during pachytene stage. An event in which the large piece of chromosome is repeated resulting in extra genetic material. Causes two or more copies of one or more genes. Duplications can occur by unequal crossing over. In inter-chromosomal duplication the duplicated segment of a chromosome is present in another chromosome of the genome. In intra-chromosomal duplication the duplicated segment remains in the same chromosome. Location may be different.

14. DUPLICATION Intrachromosomal Duplication: Tandem : In this case sequence of genes in the duplicated segment is similar to the sequence of genes in the original segment of a chromosome. Reverse tandem : the sequence of genes in the duplicated segment is reverse to the sequence of genes in the original segment of a chromosome.

15. DUPLICATION Intrachromosomal Duplication: Displaced : Duplicating segment is incorporated away from corresponding segment on the same chromosome. Translocated: Duplicated chromosomal segment is incorporated on different chromosome. A B C D E F G A B C D E F F G Effects of duplication: Origin of new genes mainly due to duplication results in evolution.  Activity of certain enzymes may be doubled. Ex: chromosome 6 of barley increased the activity of αamylase.

16. Figure of duplication

17. Inversion “A chromosomal segment is oriented in a reverse position (180o reversal )” Studied by Sturtevant & Punnet in 1921 in Drosophila. Detected by presence of inversion loop during pachytene Absence of crossing over. Paracentric Inversion: “Inverted segment does not include centromere and confined to one arm” Pericentric Inversion : “Included the centromere” Effects of Inversion: Partial male sterility. Formation of Recessive mutation. Move active genes to sites generally inactive; loose gene function and vice versa .

18. Figure of inversion

19. TRANSLOCATION “In translocation, change in position of the segment occurs in such a way that they become integrated into same or homologous or non homologous chromosome” Detected by formation of cross shaped configuration at pachytene between two non homologous chromosomes. Occurs spontaneously or may be induced by mutagens. An event in which two pieces of different chromosomes are interchanged. Chromosomal translocation may be reciprocal or Robertsonian. In Reciprocal translocation, segments from two different chromosomes are exchanged. In Robertsonian translocation, an entire chromosome is attached to another chromosome at centromere. In humans it only occur with chromosomes 13, 14, 15, 21 and 22.

20. TYPES Based on involvement of chromosomes: Intrachromosomal Translocation: Intraradial: Shift occurs in same arm. Extraradial: Shift occurs in different arm. Interchromosomal Translocation: Fraternal: Shift occurs to homologous chromosome. External: Shift occurs to non homologous chromosome. Reciprocal Translocation : “Exchange between segments of non homologous chromosomes or regions of same chromosome”. Non reciprocal Translocation: “Movement of a chromosome segment to non homologous chromosome or region of same char. without reciprocal change”.

21. TYPES Based on no. of breaks involved : Simple Translocation: “It involves one break. Terminal segment of chromosome integrated at the one end of non homologous chromosome” Shift Translocation : “It requires three breaks. Intercalary segment of a chromosome is integrated within a non homologous chromosomes” Robertsonian Translocation: “Breakage of 2 acrocentric char near centromeres & fusion of long arms. Short arms are lost” Effects of Translocation: Alters the chromosome morphology. Damage to DNA may result in formation of recessive lethal. Lead to impaired fertility.

22. Figure of translocation

23. RING CHROMOSOME Ring Chromosome: “Break occurs in each arm & the 2 sticky ends join while distal fragments are lost” A ring chromosome is a chromosome whose arms have fused together to form a ring. Were first discovered by Lilian Vaughan Morgan in 1926. Denoted by symbol r in human genetics or R in Drosophila genetics.

24. Figure of ring chromosome

25. INSERTION An event in which a piece of the chromosome is removed and inserted into a different or another chromosome. In insertion segments of DNA can also move from chromosome to chromosome. It results in loss of genetic material from one chromosome.

26. Figure of insertion

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