CHROMOSOMES The branch of biology which studies heredity and variation is called
genetics.
chromosomes are the thread like sturture present in the nucleus of cell which contain hereditary information of a cell . cromosomes are made up of dna and protiens .
THUS THE components of cromosomes are DNA and proteins. The most important component of chrmosome is ,however ,DNA . each chrmosome consists of two strands called chrmatides. the two chrmatides are joined togeter at a point called centromere . each species have a fixed number of chromosome in each of its cell,for example, the human being has 46 chromosome in every body cell . the cromosome of eacch species occur in pairs . in a pair of chrmosomes, one chromosomes comes from the father and the other from the mother. thus, human beings have 23 pairs of
homologous chromosomes ineach bady cell the 2 chromosomes in a pair of hjomologous chromosomes areof the same size and shape. but the chromosomes of one homologous pair differ in size and shape frome the chromosomes of another pair of homologous chromosomes. each chromosome of a homologous pair has genes for the same characteristics in the same place. TYPES OF CHROMOSOMES
Depending on the positon centeromere , a chromosome may have ethier equal arms or un equal arms . so, on the basis of the position of the centeromere there are 4 types of chromosomes these are :
1. Metacentric chromosome
2. Sub metacentric chromosomes 3. Areocentric chromesomes
4. Telocentric chromosome
DPLOID AND HAPLOID NUMBER OF CHROMOSOME
Each species has a fixed no. of chromosomes in its cells . for example human beings have 46 chromosome in every body cell . the 46 chromsome in an ordinary human cell are of 23 diffrent kinds so there are 2 chromosome of each kinds . the 2 chromosome of each kinds are called homologous chromosomes. A cell which has the full no. of chromosomes with two of each kind , is called a dipoid cell. in other words , a diploid cell has 2 sets of each type of chromosomes. the diploid no.of chromosomes is specific for a species . The ordinary body cell of a human being contians the full no. of 46 chromosomes , so, they are the diploid cells or they contian the diploid no.of chromosomes.