Difference Between Ovum and Egg

Ovum vs Egg

These are highly confused terms for many people, which sometimes include certain biologists who claim them to be so. However, many important differences could be easily noticed when the particulars of both egg and ovum are considered. Therefore, this article aims to discuss the particular characteristics and performs a comparison between the two entities.

What is Ovum?

Ovum is simply the female gamete. Since the nucleus of this reproductive cell contains only a half number of chromosomes as a usual cell does have, an ovum is considered as a haploid cell. Ova (plural of ovum) are present in both animals and embryophytes.

The female reproductive cell of the plants is called the gametophyte. The early stages of an ovum are known as ovules, and the lower plants do not have ova but the structures are called asoospheres. The ova in animals are produced in the gonads or ovaries through the process called oogenesis.

In most of the species of animals, ovum is easily the largest cell of the body. The largest known cell is the ovum of ostrich that becomes an egg after fertilisation. The most interesting fact of an ovum is the number of active ova at a particular time in a female is just one or very few of those.

Therefore, after the ejaculation of sperms during mating, there are millions of sperms fighting for the one and only ovum to pass the genetic substances. However, the ovum is produced after few steps of producing a haploid nucleus through meiosis.

The production of yolk is very important to enrich the foetus after the prospected fertilisation. Usually, the mammals have only a small amount of yolk in their ova while reptiles, fishes, birds, and other animals have a considerable amount of yolk since the females do not feed their embryos during embryonic development.

What is Egg?

Egg is the fertilised state of an ovum with the genetic materials of a male gamete. In fact, an egg could be defined as the organic vessel that facilitates the embryonic development for a zygote. For an ovum to become an egg, the transfer of the genetic material should have to take place.

Only the animals do have eggs for their zygote development; the similar functional structures in plants are called seeds or spores. Birds, reptiles, amphibians, fishes, insects, and even some of the mammals (monotremes) start their lives as an egg.

Eggs are capable of withstanding many environmental conditions with a hard and calcified external shell. However, only the eggs that are laid out of water viz. birds, reptiles, and montremes have a hard external shell. Ostrich has the largest known egg or the cell among all the currently living animals, and that weighs over 1500 grams and has a length of slightly less than a foot.

What is the difference between Ovum and Egg?

  • Ovum is an unfertilised female gamete, while an egg is the fertilised state of the ovum. Therefore, ovum contains only maternal genes, but egg contains both maternal and paternal genes.
  • The genetic materials in an ovum are haploid while an egg has diploid state genetic materials.
  • Ovum usually does not have a hardened shell, but eggs could have such external cover in cases of terrestrial vertebrates.
  • The term ovum is used in other life forms other than animals as well, while the term egg is used only to refer the animal zygotes developed outside their bodies.
  • An ovum is always found inside the body of a plant or animal, whereas an egg is usually an encased structure laid to the exterior of the body of an animal.

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