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The normal order of development of features in an embryo is determined by gene sequences - VCE - SSCE Biology - Question 12 - 2007 - Paper 1
Question 12
The normal order of development of features in an embryo is determined by gene sequences. The relevant groups of genes have been studied extensively in insects and c... show full transcript
Worked Solution & Example Answer:The normal order of development of features in an embryo is determined by gene sequences - VCE - SSCE Biology - Question 12 - 2007 - Paper 1
Step 1
If the action of a particular gene in a sequence was blocked
Answer
If a gene responsible for the development of an important structure such as legs is blocked, this would prevent the insect from developing that particular body part.
Thus:
- An insect with a blocked gene 4 (which is responsible for leg development) may still develop a thorax (from gene 3), but it would not develop legs.
- Consequently, option B is supported: 'an abnormal insect could develop possessing a thorax and legs but no head.'
In the context of chordates:
- If gene 8, responsible for limb development, is blocked, it would mean that limbs cannot develop, but it does not inherently prevent digits (which develop from gene 13) from forming.
- Therefore, it is plausible for an abnormal chordate to develop digits but no legs, thereby supporting option D: 'an abnormal chordate could develop possessing digits but no legs.'