spindle-fiber structure because this is used to divide cells; cancer is just cells dividing way too much. so if the <em>spindle-fiber structure </em>were to fail it could cause cancer.
Crossing over occurs between prophase I and metaphase I and is the process where two homologous non-sister chromatids pair up with each other and exchange different segments of genetic material to form two recombinant chromosome sister chromatids. So the answer would be Prophase l. Hope this helps
Answer:
autosomal defects are lethal to the fetus
