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Chromosomal Disorders


  1. Autosomes are categorized into 7 subgroups A-G. Smallest autosome is 22. Among sex chromosomes y is smaller
  2. than X
  3. Karyotype map is made on the basis of size. In Denver’s size system X-chromosomes comes between autosomes 6 & 7
  4. Chromosomal studies can be conducted on lymphocytes, bone marrow cells, fibroblasts, amniotic fluid cells,
  5. chorionic villous cells and fetal blood (but NOT on monocytes)
  6. Karyotyping cells are cultured and cell division is arrested in prophase/metaphase and then stained. Trypsin-Giemsa stain-is used for studying G bands Quinacrine stains for Q bands.
  7. Fluorescent DNA probe are used to indentify homologous DNA segments using FISH Feulgen reaction is used to detect DNA
  8. If non-disjunction occurs in mitosis, moxaic pattern occurs is somatic tissue. Often have manifestations of genetic syndromes
  9. Inactive X-Chromosome is seen as Barr body/sex chromatin in buccal mucosa & epidermis and as drum stick in neutrophils
  10. Number of bar bodies = no. of x-1 (e.g. in Klinefelter it is 1 & in super female xxx it is 2)

Chromosomal Association

Chromosome 1         :       Rh system, neuroblastoma

Chromosome 2         :       Cystinuria, hypobetalipoproteinemia

Chromosome 3         :       RCC, alkaptonuria

Chromosome 4         :       Huntington’s chorea, achondroplasus, Parkinson’s disease.

Chromosome 5         :       FAP & Colorectal carcinoma (5q), cru-du-chat syndrome

Chromosome 6         :       HLAs system/MHC antigens of 6p. DM

Chromosome 7         :       Cystic fibrosis

Chromosome 8         :       Osteopetrosis

Chromosome 9         :       ABO blood group Ag, Friedreich’s ataxra

Chromosome 11       :       Gene for β-globin chain is located so mutation result in sickle cell ds.

                                       Β-thalassemia. Wilm’s tumor. MEN1, ataxia telangiectasia, human insulin gene, PTH gene

Chromosome 12       :       PKU, vWF, carcinoma testis

Chromosome 13       :       Retinoblastoma (13q14), osteosarcoma, Wilson’s disease

Chromosome 14       :       Alpha-1 Antitrypsin-deficiency, familial HOCM

Chromosome 15       :       Marfan’s syndrome, albinism, Prader willi syndrome, Angelman syndrome

Chromosome 16       :       α-thalassemia, adult polycystic kidney disease

Chromosome 17       :       Breast carcinoma, medulloblastoma, neurofibromatosis, ovarian tumour

Chromosome 19       :       Myotonia dystrophica, gene for insulin receptor

Chromosome 20       :       MODY type1-DM, Prions disease (CJD)

Chromosome 21       :       Homocystinuria, amyloidosis

Chromosome 22       :       Meningioma, acoustic neuroma, DiGeorge syndrome

Chromosome 23       :       Gene for androgen insensitivity (testicular feminization) syndrome, fragile-X syndrome (Xq27)


  1. Transferable drug resistance is seen in Enterobacteriaceae, vibrio ,pseudomonas, Pasteurella.
  2. Transposons are called jumping gene.
  3. Plasmids are circular DNA molecules present in the cytoplasm of bacteria, capable of autonomous replication.
  4. Bacteriophage are viruses that parasitize bacteria and consist of a nucleic acid core and a protein coat.
  5. The plasmids determining penicillin resistance in staphylococci are transferred from cell to cell by transduction.

Important points to Remember

Single Nucleotide Polymorphism (SNP): Trans genomic Wave Denaturing High Performance Liquid Chromatography (Wave /DHPLC) is an approach that can detect single base pair differences between otherwise identical 750 bp fragments of DNA.

  1. BLAST: (Basic Local Alignment Search Tool) is used to compare short sequences of proteins & nucleic acids
  2. Entrez Gene & Hap Map are used to identify single nucleotide polymorphism that may contribute to pathological conditions
  3. CD ART, MMDB, and VAST are used to analyze the domain structure & 3-d structure of proteins
  4. ARS : autonomously replicating sequence; the origin of replication in yeast
  5. Copy number variation (CNV): changes in the copy number of specific genomic regions of DNA between two or more in dividuals CNVs can be as large as 106 bp of DNA and include deletions or insertions.
  6. ENCODE project : encyclopedia of DNA elements project : an effort of multiple laboratories throughout the world to provide a detailed, biochemically informative representation of the human genome using high throughput sequencing methods to identify and catalog the functional elements within a single restricted portion ( ~1 % ; 30,000,000 bp) of one human chromosome
  7. Epigenetic code: the patterns of modification of chromosomal DNA ( i. e. cytosine methylation ) and nucleosome histone post-translational modifications. These changes in modification status can lead to dramatic alterations in gene expression. Notably though, the actual underlying DNA sequence involved does not change
  8. Microsatellite repeat sequences: dispersed or group repeat sequences of 2-5 bp repeated upto 50 times. May occur at 50-100 thousand locations in the genome
  9. miRNAs: micro RNAs, 21-22 nucleotide long RNA species derived from RNA polymerase II TRASCRIPTION UNITS, 500-1500 bp in length via RNA processing. These RNAs recently discovered, are thought to play crucial roles in gene regulation
  10. PAC : a high capacity (70-95kb) cloning vectors based upon the lytic E. coli bacteriophage P1 that replicates in bacteria as an extra chromosomal element
  11. RT-PCR : a method used to quantitate mRNA levels that relies upon a first step of cDNA copying of mRNA catalyzed by reserve transcriptase prior to PCR amplification and quantitation
  12. SiRNAs : Silencing RNAs, 21-25 nucleotides in length generated by selective nucle lytic degradation of double-stranded RNAs cellular or viral origin.  SiRNAs anneal to various specific sites within targer in RNAs leading to mRNA degradation, hence gene “know down”
  13. SNP: single nucleotide polymorphism. Refers to the fact that single nucleotide genetic variation in genome sequence exists at discrete loci throught the chromosomes. Measurement of allelic SNP differences is useful for gene mapping studies.
  14. snRNA: small nuclear RNA this family of RNAs is best known for its role in mRNA processing Bioengineering: the application of engineering to biology and medicine.
  15. Bioethics: the area of ethics that is concerned with the application of moral and ethical principles to biology and medicine
  16. Biophysics : the application of physics and its technics to biology and medicine
  17. Gene therapy : applies to the use of genetically engineered genes to treat various diseases
  18. Genomics : the genome is the complete set of genes of an organism and genomics is the in depth study of the structures and functions of genomes
  19. Glycomics: the glycome is the total complement of simple and complex carbohydrates in an organism. Glycomics is the systematic study of the structures and functions of glycome
  20. Lipidomics: the lipidome is the complete complement of lipids found in an organism. Lipidomics is the in depth study of the structures and functions of all members of the lipidome and of their interactions, in both health and disease
  21. Metabolomics: the metabolome is the complete complement of metabolites found in an organism. Metabolomics is the in-depth study of their structures, functions, and changes in various metabolic states.
  22. Molecular diagnostics : the use of molecular approaches ( e g DNA probe ) to assist in the diagnosis of various biochemical, genetic, immunologic, microbiologic, and other medical conditions
  23. Nutrigenomics: the systematic study of the effects of nutrients on genetic expression and also of the effects of genetic variations on the handling of nutrients.
  24. Pharmacogenomics : the use of genomic information and technologies to optimize the discovery and development of drug targets and drugs
  25. Proteomics: the proteome is the complete complement of proteins of an organism. Proteomics is the systematic study of the structures and functions of proteomes, including variations in health and disease
  26. Stem cell biology: a stem cell is and undifferentiated cell that has the potential to renew itself and to differentiate into any of the adult cells found in the organism. Stem cell biology is concerned with the biology of stem cells and their uses in varios diseases.
  27. Synthetic biology: the field that combines biomolecular technics with engineering approaches to build new biological functions and systems.
  28. Transcriptomics: the transcriptome is the complete set of RNA transcripts produced by the genome at a fixed period in time. Transcriptomics is the comprehensive study of gene expression at the RNA level

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