INTRODUCTION TO CYTOGENETICS, chromosome.pptx

cytogenetics

1. Introduction to cytogenetics MITHUN VENUGOPAL

2. genetics Genetics is the scientific study of genes and heredity—of how certain qualities or traits are passed from parents to offspring as a result of changes in DNA sequence.

3. cytogenetics Cytogenetics is “the study of chromosomes, which involves testing samples of tissue, blood, or bone marrow in a laboratory to look for changes in chromosomes, including broken, missing, rearranged, or extra chromosomes. Changes in certain chromosomes may be a sign of a genetic disease or condition or some types of cancer.

4. DNA Self-replicating material that is present in nearly all living organisms as the main constituent of chromosomes. DNA is the chemical compound that contains the instructions needed to develop and direct the activities of nearly all living organisms. DNA molecules are made of two twisting, paired strands, often referred to as a double helix.

5. DNA Each DNA strand is made of four chemical units, called nucleotide bases, which comprise the genetic "alphabet“. The bases are adenine (A), Thymine (T), Guanine (G), and Cytosine (C). Bases on opposite strands pair specifically: A always pairs with T and C always pairs with G.

6. DNA The order of these base pairs determines the meaning of the information encoded in that part of the DNA molecule just as the order of letters determines the meaning of a word. An organism's complete set of DNA is called its Genome . Virtually every single cell in the body contains a complete copy of the approximately 3 billion DNA base pairs, that make up the human genome.

7. GENE Gene refers to the continuous segment of DNA that carries the instructions for making a specific protein or set of proteins. Gene holds the information to build and maintain their cells and pass genetic traits to offspring. Located on 23 pairs of chromosomes packed into the nucleus of a human cell.

8. GENE Genes direct the production of proteins with the assistance of enzymes and messenger molecules. Specifically, an enzyme copies the information in a gene's DNA into a molecule called messenger Ribo -Nucleic Acid (mRNA). The mRNA travels out of the nucleus and into the cell's cytoplasm, where the mRNA is ribosome, and the information is used to link together small molecules called amino acids in the right order to form a specific protein.

9. GENE Proteins make up body structures like organs and tissue, as well as control chemical reactions and carry signals between cells. If a cell's DNA is mutated, an abnormal protein may be produced, which can disrupt the body's usual processes and lead to a disease such as cancer.

10. GENE

11. CHROMOSOMES Chromosomes are thread-like structures located inside the nucleus of a cell. The term chromosome comes from the Greek words for color (chroma) and body (soma). Scientists gave this name to chromosomes because they are cell structures, or bodies, that are strongly stained by some colorful dyes used in research.

12. CHROMOSOMES Normally humans have 46 chromosomes in each cell, divided into 23 pairs, 22 pairs of autosomes and one pair of sex chromosomes (XX in females and XY in males). Two copies of chromosome, one copy inherited from each parent, form one of the pairs. Chromosome-1 is the largest human chromosome, spanning about 249 million DNA base pairs and representing approximately 8 percent of the total DNA in cells.

13. CHROMOSOMES The unique structure of chromosomes keeps DNA tightly wrapped around spool-like proteins, called histones . Without such packaging, DNA molecules would be too long to fit inside cells. For example, if all of the DNA molecules in a single human cell were unwound from their histones and placed end-to-end, they would stretch 6 feet.

14. CHROMOSOMES The only human cells that do not contain pairs of chromosomes are reproductive cells, or gametes, which carry just one copy of each chromosome. When two reproductive cells unite, they become a single cell that contains two copies of each chromosome.

15. STRUCTURE OF CHROMOSOME

16. STRUCTURE OF CHROMOSOME The constricted region of linear chromosomes is known as the centromere . Although this constriction is called the centromere, it usually is not located exactly in the center of the chromosome and, in some cases, is located almost at chromosome's end. Centromeres help to keep chromosomes properly aligned during the complex process of cell division.

17. STRUCTURE OF CHROMOSOME The regions on either side of the centromere are referred to as the chromosome's arms. Telomeres are repetitive stretches of DNA located at the ends of linear chromosomes. They protect the ends of chromosomes in a manner similar to the way the tips of shoelaces keep them from unravelling. In many types of cells, telomeres lose a bit of their DNA every time a cell divides. Eventually, when all of the telomere DNA is gone, the cell cannot replicate and dies.

18. STRUCTURE OF CHROMOSOME White blood cells and other cell types with the capacity to divide very frequently have a special enzyme that prevents their chromosomes from losing their telomeres. Because they retain their telomeres, such cells generally live longer than other cells. Telomeres also play a role in cancer. The chromosomes of malignant cells usually do not lose their telomeres, helping to fuel the uncontrolled growth that makes cancer so devastating.

19. STRUCTURE OF CHROMOSOME Chromosomes are assigned a long arm and a short arm, based on the position of their centromeres. The shorter arm of the chromosome is known as the p, or petite arm, from the French word for "small.“ The longer arm is known as the q, or queue arm, from the word meaning a line of people.

20. STRUCTURE OF CHROMOSOME Thus, chromosomal regions that are present on the short arm will begin with the designation p, whereas regions on the long arm will begin with q. By convention, the p arm of the chromosome is always shown at the top in a karyotype.

21. STRUCTURE OF CHROMOSOME Each arm of the chromosome is then divided into regions, and the numbers assigned to each region get larger as the distance from the centromere to the telomere increases. The regions are named p1, p2, etc., on the short arm and q1, q2, etc., on the long arm. Depending on the resolution of the staining procedure, it may be possible to detect additional bands within each region, which are designated by adding another digit to the number of the region, once again increasing in value as the distance from the centromere increases.

22. CLASSIFICATION OF CHROMOSOMES BASED ON CENTROMERIC POSITION Metacentric : Centromere is in the middle (1,3,16,19,20) Sub metacentric : Centromere is located at some distance from the end leading to a short ‘p’ arm and a longer ‘q’ arm (2,4 to 12, 17,18, X)

23. CLASSIFICATION OF CHROMOSOMES Acrocentric : Centromere is nearer to the short arm (13 to 15, 21, 22, Y). Most of the acrocentric chromosomes except Y have satellite bodies on their ‘p’ arm, with a secondary constriction separating them. Telocentric : Centromere is located at the terminal end of the chromosome. A telocentric chromosome has therefore only one arm.

24. CLASSIFICATION OF CHROMOSOMES

25. CLASSIFICATION OF CHROMOSOMES BASED ON THE SIZE AND LENGTH Group A: 1-3 Group B: 4-5 Group C: 6-12, X Group D: 13-15 Group E: 16-18 Group F: 19-20 Group G: 21-22, Y