GENETICS . (DR.Kumar.k.v Professor, Anatomy 05/03/2012)

This is hereditary

GENETICS The study of Genes and statistical law that govern the passage of genes from one generation to the next. Children of the same parents resemble each other and also with their parents. Genes: The characters are determined by GENES which are fundamental unites of inheritance. An individual inherits genes from both parents

CHROMOSOMES Chromosomes are present in the nucleus. Nucleus of non dividing cells shows tread like material called CHROMATIN. They are seen throughout the nucleus. Some chromatins shows dark areas(Hetero chromatine) and some shows light areas(Eu chromatin). The chief chemical in chromatin is DNA.

CHROMOSOMES The chromatin condense and coil tightly to form Chromosomes. The so called chromosome shape can seen only during cell division. During resting stage of the cell no chromosomes are seen, but only chromatin. Chromosomes are seen only during Metaphase of the cell division.

Chromosome Number. 46 chromosomes in every cell except in sperm and ovum .Also called as DIPLOID STATE or 2n. In the gametes during meiosis cell division the number becomes half to23.This state is also called n or Haploid. When 23 chromosomes from the father and 23 from the mother unites during fertilization the original 46 chromosome number is reestablished.

Normal male karyotype. 444+XY

Autosomes and the Sex chromosomes The total number of 46 chromosomes are further divided into two groups. 22 pairs of AUTOSOMES and 1 pair of SEXCHROMOSOMES. Two chromosomes forming a pair is similar in length and shape and one comes from the father and the other come from the mother. So this similar looking chromosomes are called as HOMOLOGOUS pair of chromosomes.

Male karyotype 44+XY

SEX CHROMOSOMES. The sex chromosomes are two kinds X and Y. The human female has 44 autosomes and two X chromosomes.(44+XX). The human male has 44 autosomes and one X and one Y chromosomes which are dissimilar in length and shape.(44+xy). Chromosomes are only visible with the help of a Microscope, while cell is undergoing division, during Metaphase.

NORMAL FEMALE KARYOTYPE-XX

Structure of the chromosomes Each metaphase chromosome will have two similar limbs running parallel to each other. The arms or the limbs are called as chromatids. (P and Q limbs)long and short arms. Centromere: The light staining constricted area usually placed in the center of the chromatids. The position of the centromere is the PROMARY CONSTRICTION.

CLASSIFICATION OF THE CHROMOSOMES 1.The position of the Centromere: is different in different chromosomes. This fact is utilized for the classification. Metacentric: The centromere is located at the center. Submetacentric:The centromere is located little away from the center. Acrocentric: The centromere is very close to the end. Telocentric: Centromere at the extreme end and have only one arm

Metacentric/sub metacentric/telocentric Chromosomes. Note the position of the centromere:

Meta/sub/acro/telocentric Chromosomes

Denver classification Chromosomes are classified into SEVEN GROUPS according to their descending length. The groups are designated as A TO G. Female X chromosome in C (very long) group and male Y chromosome in G (very short). Paris NomenclatureBanding technique: According to this method each arm of (chromatid) chromosome is further divided

Banding technique Into 2 or 3 region and each region is again divided into BANDS. This is called banding technique. With this banding technique minor structural details of the individual chromosomes can be identified and it is more accurate for the identification of any structural defect.

Banding pattern

Chromosomal analysis and Karyotyping Karyotype: The arrangement of all the chromosomes in a specific sequence is called as karyotype. Why karyotyping done?: Sex determination. Congenital malformation. Mental retardation. Prenatal diagnosis. Repeated abortion

Karyotyping Karyotyping helps to proper identification and the numbering of the chromosomes. Numerical and structural abnormalities can easily be identified. Preparation:fast dividing metaphacic cells are selected.(lymphocytes,bone marrow cells,fibroblasts,placental cells,cells from the amniotic fluid)

Lymphocytes 5ml of venous blood is collected. Mix with heparin to avoid clotting. Cells are then incorporated into culture media(growth media) contains fetal calf serum, and Phytohaemagglutinin.Phytohaemagglutinin stimulate fast cell division. Antibiotics are also added to prevent infection.

Metaphase spread The cells are put into incubator for 72 hours and at the end of 3 days COLCHICIN is added to arrest the cell division at metaphase where the chromosomes are clearly seen. The metaphase cells are then separated using a centrifuge. The cells are dropped from a height to a chilled slide. Cell spread is thus made.

UNSORTED(NOT ARRANGED)CHROMOSOMES Chromosomes before karyotyping

Final step in Karyotype The slides are then stained and micro –photographed. The individual chromosomes are cut and arranged according to the length and made into homologous pairs.(looking similar) They are named A-G based on the longest on the top rows and shortest at the bottom rows.

HUMAN MALE KARYOTYPE-MALE or FEMALE?

HUMAN FEMALE /MALE KARYOTYPE?

BAR BODY OR SEX CHROMATINE. The female nucleus has 2x chromosome. A dark stained chromatin mass attached to the one side of the nuclear membrane. This dark mass is called as BARR BODY or sex chromatin.(note the arrow marked area in the next diagram) This utilized to identification of the sex(seen only in normal female and absent in normal male)

LYONS HYPOTHESIS/BARR BODY