What is Genetics?
The science of Genetics defines and analyzes heredity, or constancy and change in the vast arrangement of physiologic functions that form the properties of organisms.
* The unit of heredity is the Gene :
- a segment on a DNA molecule.
- usually at a specific location (locus) on a chromosome or plasmid.
- characterized by its nucleotide sequence.
* Genotype:- alteration in the sequence of DNA within a gene or in the organization of genes .
* Phenotype:- the collective structural and physiologic properties of a cell or an organism, ex. eye color in a human or resistance to an antibiotic in a bacterium.
Genetic Elements:-
The structure of nucleic acids (DNA & RNA):
1. composed of chains of nucleotides.
2. a nucleic acid molecule may contain several thousands or millions of nucleotides.
3. nucleic acid molecules are usually composed of
4 different nucleotides.
4. each nucleic acid molecule has its own order, or “sequence,” of nucleotides.
5. The correct sequence of nucleotides is essential for the nucleic acid’s function.
Nucleotide structure:-
- A nucleotide consists of:
• nitrogenous base
• pentose sugar
• phosphate group
- Nitrogenous bases:
• purines: adenine & guanine
• pyrimidines: cytosine, thymine (in DNA), & uracil (in RNA)
– Pentose sugars:
• Ribose (found in RNA)
• Deoxyribose (found in DNA)
DNA: Deoxyribonucleic acid:-
– nitrogenous bases:
adenine and guanine (purines)