Describe the roles of the enucleated egg cell and the diploid nucleus in the process of cloning a mammal by somatic cell nuclear transfer.

Pearson Edexcel International GCSE Biology (4BI1) — 5.4 Cloning · Describe · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Dolly the sheep was the first mammal to be cloned from an adult somatic cell using a technique called somatic cell nuclear transfer. The process involves combining material from two different cells to produce a clone of the donor organism.

Model answer (4 marks)

The enucleated egg cell has had its nucleus removed, so it contains no genetic material.
The diploid nucleus from a somatic cell of the donor organism is inserted into the enucleated egg cell.
The diploid nucleus supplies the complete set of chromosomes required for development.
The resulting cell is stimulated to divide and develop into an embryo genetically identical to the donor.

Examiner tips

Use the exact phrases "enucleated egg cell" and "diploid nucleus". Show the sequence: removal, insertion, genetic supply, stimulation to divide. Keep answer to four short points to match the four marks.

Common mistakes

Confusing the roles of the egg and the nucleus. Using singular/plural incorrectly (e.g., "diploid nucleus" vs "diploid nuclei"). Omitting the stimulation to divide step.

Mark scheme (4 marks)

The enucleated egg cell has had its nucleus removed / the nucleus is removed from the egg cell so it contains no genetic material
A diploid nucleus from a somatic / body cell of the organism to be cloned is inserted into the enucleated egg cell
The diploid nucleus provides the full / complete set of genetic information / all the chromosomes needed to develop into a new organism
The resulting cell is stimulated to divide / develop into an embryo that is genetically identical to the donor organism

Key terms in this question

enucleated egg cell · diploid nucleus · somatic cell nuclear transfer · cloning