Gene mutation and chromosomal mutation.pptx

Gene mutation and chromosomal mutation

1. Chromosomal Aberrations and Gene mutation Dr. Rikesh Shrestha

2. Difference between Gene and Chromosome Both hold information. Chromosomes has many genes. Genes hold information to built specific proteins.

3. Chromosomal Mutation The changes in the structure and number of chromosomes. Also called as chromosomal aberrations. These are produced by misrepair of broken chromosomes, by improper recombination or malsegregation of chromosomes during mitosis and meiosis. Types – Changes in the structure of chromosomes. Changes in the number of chromosomes.

4. Types Changes in the structure of chromosome Duplication Deletion Inversion Translocation Change in the number of chromosome Aneuploidy Euploidy

5. Change in the structure of the chromosomes

6. Deletion A segment of chromosome is lost. D/t lag during anaphase and digestion by nucleases. Two types – Terminal deletion and intercalary deletion. In terminal deletion, a terminal segment is lost while in intercalary deletion, an intermediate segment of chromosome is lost.

7. Duplication A segment is repeated. When the duplication is present, the chromosome supplied with extra segment forms loop to match the position of homologous chromosomes.

8. Inversion A segment of chromosomes breaks and reunites in the reverse order. There is no loss or gain of genes. But are arranged in reverse order. 2 types – Pericentric and paracentric . In pericentric inversion, centromere is included in the inverted segment. In paracentric inversion, the centromere is not included in the inverted segment.

9. Translocation Non- homologous chromosomes exchange segments. No net gain or loss of chromosome 2 main types Reciprocal Translocation Robertsonian Translocation

10. Reciprocal Vs Robersonian Translocation Reciprocal Translocation- 2 different chromosomes have exchanged segments with each other. Robertsonian Translocation- Entire chromosome attaches to another at the centromere.

11. Changes in the number of chromosomes Change in the number of chromosomes is called ploidy. D/t loss or gain of chromosome of a set or changes in the number of chromosomes. Two types- Aneuploidy Euploidy

12. Aneuploidy Where there is addition or loss of one or more chromosomes in a set. Caused by non- disjunction ( Failure of homologous chromosomes or sister chromatids to separate properly during cell divisions ) of chromosomes. 3 Types Monosomy Nullisomy Trisomy

13. Monosomy One chromosome is lost from a pair, Represented by 2n-1 The monosomic individual has one chromosome less from the normal number of chromosomes. Turner Syndrome (Egg without X chromosome fuse with sperm containg X chromosome).

14. Nullisomy Where both chromosomes of a pair are lost . Represented by 2n-2. Nullisomy is produced by the fusion of gametes having one chromosome less . Nullisomy individual cant survive.

15. Trisomy One chromosome is added to a pair. Represented by 2n+1 Caused by non- disjunction . Klinefelter Syndrome – During gamete formation extra X chromosome (Either XX from mother, Y from father or X from mother XY from father). Down‘s syndrome.

16. Euploidy Change in the number of chromosome sets . 2 types Haploidy Polyploidy

17. Haploidy The basic set of chromosome in any species is haploid . Represented by N number. Gametes carry haploid number of chromosomes. During fertilization, the parental combination unite together to form diploid chromosome (2N). Some times in life of an animal, a set of chromosome will be lost leading to haploidy .

18. Polyploidy Condition in which an organism contains mor e than the usual 2 sets of chromosomes. Triploids (3N) Tetraploids (4N) Pen- ploids (5N) Hexaploids (6N) During gamate formation , the homologous chromosomes may not separate completely, resulting in diploid number of chromosomes.

19. Gene Mutation Change in the base sequence of the genes. Change in the structure of DNA. Point Mutation (Occurs when the base sequence of a codon is exchanged) (GCA - GAA) Frame Shift Mutation- A change of the reading frame is called frameshift mutation.

20. Gene Mutation Change in amount or structure of DNA of an organism. Cause of Mutation - Also k/a mutagens There are certain physical and chemical agents which causes inheritable changes in a gene called mutagens.

21. Types of Mutagens Ionizing Radiation – High energy radiations like alpha, beta, gamma and cosmic rays. Called because they penetrate tissues deeply and ionization of encountered molecules. Electron forced to flow out of molecules and atoms are transferred into free radicals and reactive ions . Altering in purines and pyrimidines in the DNA. Non- Ionizing Radiation – UV Rays. Effects mainly pyrimidines to cause change in DNA. Chemical mutagens – Certain chemicals like nitrous acid hydroxylamine, formaldehyde, certain component of tobacco, food preservatives, pesticides, etc.

22. Types Induced Mutations- Artificially produced mutation. Eg . X- rays, nitrous acid, etc Spontaneous Mutation – Naturally occurring. D/t normal cellular operations or due to random interaction with environment.

23. Point Mutation When single base pair is altered Types – Base substitution – One base is replaced by another base. Base insertion – A new base is inserted. Base deletion – A base is missing. Base inversion – The base sequence is reversed.

24. Missense mutation Sometimes in a polypeptide chain, an amino acid is substituted by another amino acid. This is d/t substitution of three bases (a codon) in the DNA.

25. Non- sense mutation Sometime mutation produces a base sequence that doesn’t code for any amino acid (non- sense codon) Termination of the synthesis of protein occurs. A non sense mutation is a point mutation that introduces a premature stop codon into the part of the gene that encodes a protein. Instructs ribosome to stop making the protein.

26. Silent Mutation Substitution of 3 bases in the DNA may result in the substitution of a new amino acid in the polypeptide chain. When substituted amino acid is closely related to the original amino acid, mutation has no detectable effect on the phenotype of the cell.

27. Transition Point mutation where one purine base is substituted by another purine or one pyrimidine base is substituted by other pyrimidine . G-C pair is exchanged with an A-T pair vice versa.

28. Transversion Point mutation in which a purine is replaced by pyrimidine or vice versa . An A-T pair is replaced by a T-A pair

29. Frameshift mutation A mutation that inserts or deletes a single base will change the reading frame for the entire subsequent sequence. A change of the reading frame is called frameshift mutation. Induced by acridine compound that binds to DNA and distort the structure of double helix causing additional bases to be incorporated or omitted during replication.

30. THANK YOU