We use the term genome to refer to all of the alleles possessed by an organism (or by a population, species, or larger taxonomic group). While the amount of DNA for a diploid cell is constant within a species, the differences can be great between species.

Humans have 3.5 X 109 base pairs, Drosophila has 1.5 X 108, toads have 3.32 X 109, and salamanders have 8 X 1010 base pairs per haploid genome.

Much of the DNA in each cell either has no function or has a function not yet known. Eukaryotes have only 10% of their DNA coding for proteins. Humans may have a little as 1% coding for proteins. Viruses and prokaryotes use a great deal more of their DNA.

Almost half the DNA in eukaryotic cells is repeated nucleotide sequences. Protein-coding sequences are interrupted by non-coding regions. Non-coding interruptions are known as intervening sequences or introns. Coding sequences that are expressed are exons.

Genetics crucial role in life.

How would you define a gene and what it does?