macrogametes

Macrogametes are the larger, typically non-motile gametes in species that reproduce by oogamy, a form of sexual reproduction in which two distinct gametes fuse to form a zygote. They are the female or female-like gametes and are generally larger than their partners, the microgametes. Macrogametes usually contribute most of the cytoplasm and organelles to the zygote, while microgametes provide mainly DNA and, in many cases, motility.

Macrogamete production occurs in specialized structures such as oogonia in many algae and protists; in plants and animals, the term is often aligned with the egg cell. In organisms that exhibit oogamy, microgametes are typically smaller and flagellated or otherwise motile, or released to encounter the macrogamete. Fertilization is the fusion of the macrogamete with a microgamete, after which the zygote develops into a new generation. The specifics of timing and location of fertilization vary widely among taxa, from external fertilization in aquatic algae to internal fertilization in animals and many land plants.

Examples of oogamous systems include many brown and green algae, some red algae, oomycetes, as well as the eggs of animals and the ova in higher plants. In these groups, macrogametes are sometimes called eggs, while microgametes are called sperm. While the term macrogamete is most often used in the context of simple or ancient reproductive strategies, it remains a useful descriptor for contrasting with microgametes and for understanding resource allocation in fertilization.