DNA Fingerprinting

1. Tissue samples are obtained from the criminal scene and DNA is extracted

2. A restriction enzyme is added to the DNA to cut it into fragments

3. DNA fragments are separated according to size during a process called electrophoresis using an agarose gel

4. An alkali is added to separate the double stranded DNA into single strands

5. Each single strand is transferred to a nylon membrane and a radioactive probe is added to it

6. A banding pattern appears

7. An x-ray film is produced and the positions of black bands are compared with the part of DNA treated with radioactive probe

Formation of pollen grains

Pollen grains are formed in the anther. An anther has 4 pollen sacs. Each pollen sac contains hundreds of cells called pollen mother cells. Each pollen mother cell undergoes meiosis to form 4 haploid microspores. The nucleus of each microspore divides by mitosis to form a tube nucleus and a generative nucleus.