HUMAN CHROMOSOMAL ABERRATIONS AND KARYOTYPE ANALYSIS.

HUMAN CHROMOSOMAL ABERRATIONS AND KARYOTYPE ANALYSIS.

1. PADMASHREE INSTITUTE OF MANEGMENT AND SCIENCE . Seminar topic on ; HUMAN CHROMOSOMAL ABERRATIONS, Karyotype analysis Presented by; Shylesh murthy I .A 1 st yr Msc biotechnology PIMS

2. HISTORY Chromosomes were first observed in plants, investigation of human karyotype took many years to settle . In 1912 Hans von Winiwarter reported 47 chromosomes in spermatogonia and 48 in oogonia concluding XX/XO sex determination mechanism . Painter in 1922 was not certain and revised his opinion from 46 to 48 chromosomes . He correctly insisted on human having XX/XY chromosome system

3. Human Chromosomal Aberration Change in the structure and number of chromosomes are called chromosomal aberration. Its off 2 types 1. Structural and numerical abnormalites There are 4 types of structural abnormalites Deletion Duplication Inversion Translocation

4. Deletion In this type a segment of chromosome is lost its off 2 type A. Terminal ;- B. Inter calery ;- A B C D E F G A B C D E F G

5. Example ;- Cri-du-chat syndrome In human babies deletion of a segment of a chromosome at Number 5 causes Cri-du-chat syndrome Symptoms ;- it cries Like cat and its mentally retarded with small head

6. Duplication Where a segment is get repeated .Hence a set of genes is present inn double doses Normal chromosome Chromosome with duplication A B C D E F G H A B C D E F G H G H

7. During meiosis ,the duplicated segment forms a Loop These duplication produces ‘POSITION EFFECT’ Example;- Down’s syndrome Here It is a case of 21 st trisomy , ie an extra chromosome of the 21 st pair is present .hence there are 47 chromosomes (2n+1) instead of 46. formally this condition was known as mangolism . Symptoms ;- The diseased person has a characteristic fold of the eye called epicanthus . The eyes are small ,skull is large .

8. INVERSION Where the segment of the chromosome breaks and rewinds in reverse order . In inversion there is no loss or gain of genes ,but the genes are arranged in reverse order It is of 2 types ;- 1. pericentric 2. paracentric

9. Pericentiric ;- in pericentic the centromere is included in the inverted segment 2. Para centric ;- here the centromere is not included in the inverted segment

10. The chromosome with inverted segment produces an inversion loop These iversion loop prevents crossing over It brings about the position effect

11. T ranslocation Where non homologous chromosome exchange segments These translocation produces the Cross-shaped structure A B C D 5 6 7 8 1 2 3 4 E F G H Example ;- chroinic myeloid leukaemia(commonly in male Than females)

12. Here the translocatin takes place between 9 th and 22 nd chromosomes Symptoms ;- Enlarged spleen and liver. Mild fever and night sweats 3. Increase in bone marrow 4. Bone pain

13. Variation in chromosome number ( ploidy ) EUPLOIDY ANEUPLOIDY POLYIPLOIDY ( 3n ,4n ,5n) HAPLOIDY (n) DIPLOIDY (2n) Nullisomy ( 2n-2) Monosomy ( 2 n-1) Polysomy (2n+1 or 2n+2)

14. Karyotype Nageli observed in plants in 1842. Flemings observed in animals in 1882 Chromosomes arranged based on there shape ,size and structure called karyotype These karyotype of a species are represented by diagram called IDIOGRAM

15. Karyotypes can be used for many purposes as study of chromosomal aberrations The study of karyotypes is important for cell biology and genetics and the results may be used in evolutionary biology and genetics The study of karyotypes is easily made possible by staining .usually ,a suitable dye such as Giemsa ,is applied after the cells have been arrested during cell division .

16. types of banding G banding R banding C banding Q banding T banding

17. G banding is obtained with giemsa stain and following digestion of chromosomes is carried out by trypsin.darkly stained regions are known as heterochromatin and lightly stained regions are known as euchromatin .

18. R banding is the reverse of G banding ..the lightly stained regions are euchromatin and darkly stained regions are heterochromatin

19. C banding is also obtained with giemsa stain .it is used for centromere staining

20. Q banding is a fluoroscent pattern obtained using Quinacrine for staining . Pattern is similar to G banding .

21. T banding is also obtained by giemsa staining and it is carried out for visualization of telomeres. Silver staining stains the nucleolar organization region associated with proteins .

22. Example ;- GTG Banding G = G banding T = trypsin for Pretreatment G = Stain used( geimsa )

23. The normal human karyotypes contain 22 pairs of autosomal chromosomes and one pair of sex chromosomes [ allosomes ]. Normal karyotype for females contain two X chromosomes[XX] Normal karyotype for male contain one X and Y chromosome[XY] Any variation from the standard karyotype may lead to developmental abnormalities . NORMAL HUMAN KARYOTYPE

24. Abnormal human karyotype Chromosome abnormalities can be numerical as in the presence of extra or missing X chromosome . Numerical abnormalities are termed as aneuploidy .it occurs as a result of nondisjunction during meiosis in the formation of gametes Common numerical abnormality is trisomy of 21 st chromosome . Structural abberations occur from errors in homologous recombination .

25. Chromosomal abnormalities that lead to disease in humans include Downs syndrome Patau syndrome Cri du chat syndrome Klienfelters syndrome Turner syndrome

26. Trisomy 13 or D- trisomy ( Patau syndrome) Trisomy 18 or E- trisomy ( Edwardsyndrome ) Trisomy 21 or G- trisomy (Down syndrome)

27. 1 st described by Bartholin (1657) & redefined by Patau (1960). This is present in both male and females . Chromosomal complement: 47,XX,+13 (female) or 47,XY,+13 (male) Symptoms ;- Mental deficiency Low birth weight Abnormal development of frontal lobe

28. Malformed ears

29. References ; Biology DR SUDAKAR RAO- INTERNET SOURCES

30. .Thank you ……….