What are the reasons why Mary was thought to be preserved from sini?

Why didn’t they decide that sin travelled down male line only ie sins of fathers, passed down gen. to generation? Bible quote ie Adam was resp. before God although Eve sinned tooIs Is,there then a male headship rule about resp. for sin, ie fathers and husbands take a headship resp.for sin?

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About Mary…where in the Bible does it say…
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