BOTANY Higher Secondary Second Year - Textbooks Online

The genome size of an individual is expressed in terms of number of base
pairs either in kilobases (1000 bp) or in megabases (one million bp).
Arabidopsis thaliana is an annual crucifer weed called ‘thale cress’. It has
the smallest nuclear genome of 130 mb with five chromosomes (2n = 10).
The human genome comprises approximately 3.2 x 10 9 nucleotides. The
human mitochondrial genome contains 37 genes and has 16,569 basepairs.
Table showing the genome and approximate number of genes
S. No Name of the organism
Size of the genome
in megabase pairs
In human genome, 38.2% of genome is involved in biochemical
activities like synthesis of immunological and structural proteins, 23.2%
in the maintenance of genome, 21.1% in receiving and giving signals
related to cellular activities and remaining 17.5% in the general functions
of the cell. The functions of 30,000 to 40,000 human genes are known.
Self evaluation
I. Answer the following questions in two or three sentences.
1. Define a gene.
2. Why has ‘one gene one enzyme hypothesis’ been modified into
‘one gene one polypeptide hypothesis’?
3. Define genome.
4. State the percentage of human genome performing various
activities.
II. Answer the following questions in about 100 words.
5. Write short notes on genome.
115
Approximate
number of genes
1. Escherichia coli 4.64 4,400
2. Yeast 12.10 5,800
3. Arabidopsis thaliana 130.00 26,000
4. Drosophila 180.00 13,600
5. Homo sapiens 3,300.00 30,000 - 40,000