Sexual Reproduction (Rhizopus)

• Sexual reproduction in Rhizopus occurs when hyphae of opposite strains grow close together and come into contact.
• Hyphae can be of a plus (+) strain type or a minus (-) strain type.
• Sexual reproduction can only occur between a plus and a minus strain.
• Chemotropism attracts the hyphae to one another (hyphae release chemicals).

Sexual Reproduction in Rhizopus

1. Two hyphae of opposite strains grow close to one another.
2. Swellings develop on each hypha.
3. Nuclei (sex cells/gametes) move into each swelling. Each swelling is now called a progametangium.
4. The swellings touch and cross walls form behind the progametangia, dividing them from the rest of the hyphae. The progametangia are now called gametangia.
5. The end walls between the gametangia break down. The nuclei mix.
6. Fertilisation occurs as two haploid (n) nuclei join. A diploid zygote is formed (2n).
7. A tough wall forms around the zygote, creating a zygospore.
8. The parent hyphae die. The zygospore remains dormant until conditions become favourable.
9. When conditions are suitable, the zygospore germinates. The diploid zygote divides by meiosis and a new haploid hypha forms.
10. The new hypha forms a sporangium, which disperses haploid spores to restart the life cycle.