DNA / Chromosomes/ Genes
Each human being has characteristics passed on to them by their parents.
Each characteristic, such as hair colour, height, eye colour, skin colour is called traits
The instruction for each trait is located on chromosome, which found in the nucleus of cells
The segment of DNA located in chromosomes are called Genes, that control the production
of proteins
Each chromosome consists of hundreds of genes, each gene playing an important role in
determining the characteristics and functions of cell
Each species has a characteristic number of chromosomes in each cell
Humans have 46 chromosomes, consisting of 23 pairs of autosomes and a pair of sex
chromosomes: two X sex chromosomes for females (XX) and an X and Y sex chromosome for
males (XY). One member of each pair of chromosomes comes from the mother; one
member of each pair comes from the father.
Structure of chromosomes
The nucleus of each cell in our body contains DNA. this DNA is tightly packed into a structure
called chromosomes.
Chromosomes are rod-shaped structure made of DNA and protein
In eukaryotes, DNA wraps around proteins called histones to help maintain the compact
structure of chromosomes
The chromosomes consist of two identical halves. Each half of the chromosome is called a
chromatid
The two chromatids of a chromosome are attached at a point called a centromere. the
centromere holds the two chromatids together.
Structure of DNA and genes
DNA (deoxyribonucleic acid) is a double helix molecule made of two antiparallel strands of
nucleotides linked by hydrogen bonding. It is molecule that carries the genetic information
in all cellular forms of life.
It belongs to a class of molecules called the nucleic acids, which are polynucleotides – that is
long chains of nucleotides
Each nucleotide consists of three components
1. A nitrogenous base : cytosine ( C ) , guanine ( G ) , adenine ( A) or thymine ( T)
2. A five caron sugar molecule
3. A phosphate molecule
What is a gene ?