Download
1 / 38
E N D
4. Objectives To know the normal structure and number of human chromosomes (Cytogenetics)
To be introduced briefly to various methods of human chromosomes staining.
To understand the Condensation/Decondensation, and Packing of chromosomes.
To know the definitions of genotype and phenotype.
To understand the relation between genotype & phenotype
To know various patterns of inheritance
To understand the methods of regulation of gene expression.
To differentiate between gene expressivity, and gene penetrance.
To be familiar with genetic heterogeneity with clinical examples.
To know how new mutation can explain the new appearance of AD disease.
To know how are the genes with co-dominant alleles expressed.
5. Genetic Material in the Living Cells * All living organisms are made up of cells.
* Cells contain a nucleus surrounded by a nuclear membrane in eukaryotic cells, and a nuclear region in the prokaryotic cells.
6. Genetic Material in the Living Cells
8. Genetic material…contd The study of chromosomes, their structure and their inheritance is known as Cytogenetics.
Each species has a characteristic number of chromosomes and this is known as karyotype.
Prior to 1950's it was believed that humans had 48 chromosomes but in 1956 it was confirmed that each human cell has 46 chromosomes (Tjio and Levan, 1956).
9. Genetic material…contd The genes are situated on the chromosomes in a linear order. Each gene has a precise position or locus.
11. * The ‘Human Genome Project’: (Conti.) The draft DNA sequence of 3 billion base pairs was completed in 2000
The complete sequence was announced in 2003 (2 years ahead of its allocated end)
~ 30,000 genes
12. Chromosomes * One member of each chromosome pair is derived from each parent.
* Somatic cells have diploid complement of chromosomes i.e. 46.
* Germ cells (Gametes: sperm and ova) have haploid complement i.e 23.
* The chromosomes of dividing cells are most readily analyzed at the `metaphase' or prometaphase stage of mitosis .
13. The Normal Human Chromosomes * Normal human cells contain 23 pairs of homologous chromosomes:
- 22 pairs of autosomes (numbered as 1-22 in decreasing order of size)
- 1 pair of sex chromosomes.
* Autosomes are the same in males and females
* Sex chromosomes are:
- XX in females
- XY in males.
* Both X are homologous. Y is much smaller than X and has only a few genes.
14. Chromosome Structure
* At the metaphase stage each chromosome consists of two chromatids joined at the centromere or primary constriction
The centromere divides chromosomes into short (p = petit) and long (q; g = grand) arms. The tip of each chromosome is called telomere.
The exact function of the centromere is not clear, but it is known to be responsible for the movement of the chromosomes at cell division.
15. Chromosomes … contd In a non-dividing cell the nucleus is filled with a thread-like material known as "chromatin".
Before cell division, the chromatin multiplies (replicates), loses the relatively homogenous appearances and condenses to form rod like structures .
16. Each species has a characteristic gene map i.e. the chromosomal location of the genes, and it is the same in all normal individuals of each species
20. Staining Methods for cytogenetic analysis of chromosomes There are several staining methods for cytogenetic analysis of chromosomes.
Each stain produces specific banding patterns known as "Chromosome Banding"
G banding,
Q banding,
R banding,
C banding.
The pattern is specific for each chromosome, and is the characteristics utilized to identify each chromosome.
23. What is SKY?
24. Condensation-Decondensation of Chromosomes
26. Human Mitochondrial DNA
32. Gene EXPRESSIVITY
33.
34.
35.
