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
A. an abnormal insect could develop possessing a head but no legs.
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Answer
If the action of gene 4 is blocked (which is responsible for leg development), the insect can still develop a head as it's directed by gene 1. Therefore, option A is valid.
Step 2
B. an abnormal insect could develop possessing a thorax and legs but no head.
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Answer
This statement suggests gene 1 is blocked since it prevents head development. However, gene 3 (thorax development) can still function. Hence, option B is inaccurate because without gene 1 acting, a head cannot be present.
Step 3
C. an abnormal chordate could develop a thorax but no head.
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Answer
If gene 1 (head development) is blocked, but gene 4 (thorax development) is active, it is indeed possible for a chordate to develop a thorax without a head. Thus, option C is correct.
Step 4
D. an abnormal chordate could develop possessing digits but no legs.
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Answer
If gene 8 (limb development) is blocked, digits could still develop if gene 13 acts normally. Therefore, option D could be correct, but it depends on the blockage's specific effects on limb and digit expression.
