Where does this evidence come from? – crossing over takes place at a four-stranded stage and not at two stranded stages of chromosomes

Options :

1. 2:2:2:2 organization of ascospores in Neurospora

2. studies on linkage maps of chromosomes in Drosophila

3. studies of meiosis in maize

4. 4:4 organization of ascospores in Neurospora