Fig. 1 shows stages used to produce a cloned sheep from a prize ewe. The nucleus is taken from a body cell of the prize ewe and placed into an egg cell from...
Question 1 Report
Fig. 1 shows stages used to produce a cloned sheep from a prize ewe. The nucleus is taken from a body cell of the prize ewe and placed into an egg cell from another sheep.
(a) Name the cell structure labelled X that must be transferred from the prize ewe. [1]
(b) Complete the description of stages Y and Z.
Stage Y: the egg cell nucleus is removed so that the egg cell contains no __________.
Stage Z: the reconstructed cell divides by __________ to form an embryo. [2]
(c) Explain why the lamb born from the surrogate has the same inherited characteristics as the prize ewe. [4]
(d) Describe how a farmer could use cloning to increase the number of sheep with a valuable characteristic, such as resistance to a disease. [3]
(e) Explain two reasons why a flock made by cloning many sheep could be at risk if a new disease spreads through it. [4]
Answer Details
(a) Structure X is the nucleus. [1]
(b) At stage Y, the egg cell nucleus is removed so the egg contains no nucleus. At stage Z, the reconstructed cell divides by mitosis to form an embryo. [2]
(c) The donor nucleus contains chromosomes, DNA and genes from the prize ewe. Genes control inherited characteristics. Because the egg nucleus was removed, the embryo receives the prize ewe’s nuclear genetic information. Therefore the lamb has the same inherited characteristics as the prize ewe. [4]
(d) Select a sheep with the valuable characteristic. Transfer nuclei from its body cells into egg cells whose nuclei have been removed. Stimulate the cells to form embryos and implant them into surrogate sheep, producing many cloned lambs. [3]
(e) Cloned sheep have little or no genetic variation. They are likely to have the same susceptibility to a pathogen, so a new disease could infect many or all of them. Few resistant individuals would survive and reproduce, leaving the flock especially vulnerable. [4]
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