Required Practical 2

Question 1

Describe how to prepare a root tip cell squash

Answer 1

• cut thin slice of root tip
• soak in hydrochloric acid then rinse
• stain for DNA (eg. Touledine blue)
• lower coverslip using a mounted needle to prevent air bubbles
• squash by firmly pressing down glass slip

Question 2

Why is a stain used?

Answer 2

• to distinguish chromosomes
• chromosomes not visible without stain

Question 3

Why are the roots soaked in acid?

Answer 3

• separate cells
• allow stain to diffuse into cells
• allow cells to be more easily squashed
• stop mitosis

Question 4

Describe how to set up an optical microscope

Answer 4

• clip slide onto stage and turn on light
• select lowest power objective lens
• use coarse focusing dial to move stage close to lens
• adjust fine focusing dial to get clear image
• swap to higher power objective lens then refocus

Question 5

How to determine a reliable mitotic index

Answer 5

• count cells in mitosis in field of view
• only count whole cells to standardise
• divide by total number of cells in view
• repeat with many different fields of view selected randomly so representative
• calculate reliable mean