Ovum
An ovum is a haploid
female reproductive cell or gamete. The word is derived from
Latin, meaning egg or egg cell. Both
animals and
embryophytes have ova. The term ovule is used for the young ovum of an animal. In some
plants, such as
algae, it is also called oosphere.
=Material contribution to offspring=
The egg is the sole provider of such endosymbiotic
organelles, including mitochondria and chloroplasts within the cytoplasm. These cannot be produced with nuclear DNA alone and must be manufactured from DNA within existing organelles of their type — this is important in Human mitochondrial genetics and can be used to trace maternal and paternal ancestry, especially as plants contain chloroplasts as well.
Encyclopedia
An
ovum is a haploid
female reproductive cell or gamete. The word is derived from
Latin, meaning egg or egg cell. Both
animals and
embryophytes have ova. The term
ovule is used for the young ovum of an animal. In some
plants, such as
algae, it is also called
oosphere.
=Material contribution to offspring=
The egg is the sole provider of such endosymbiotic
organelles, including mitochondria and chloroplasts within the cytoplasm. These cannot be produced with nuclear DNA alone and must be manufactured from DNA within existing organelles of their type — this is important in Human mitochondrial genetics and can be used to trace maternal and paternal ancestry, especially as plants contain chloroplasts as well. Sperm are often too small to contribute anything physical except DNA and its own mitochondria gets destroyed by the egg.
Ova production
In higher animals, ova are produced by female gonads called
ovaries and all of them are present at birth in mammals, and mature via oogenesis.
Human and mammal ova
In the viviparous animals , the ovum is fertilized inside the female body, and the embryo then develops inside the uterus until it is born. It receives nutrition directly from the mother. The ovum is the largest
cell in the human body, typically visible to the naked eye without the aid of a
microscope or other magnification device. The human ovum measures on average, 145 µm in diameter.
Ova development in oviparous animals
In the
oviparous animals the ova develop protective layers and pass through the
oviduct to the outside of the body. They are
fertilized by male
sperm either inside the female body , or outside . After fertilization, an
embryo develops, nourished by nutrients contained in the egg. It then hatches from the egg, outside the mother's body. See egg for a discussion of eggs of oviparous animals.
The egg cell's
cytoplasm and
mitochondria are the sole means of the egg being able to reproduce by
mitosis and eventually form a blastocyst after fertilisation.
Ovoviviparity
There is an intermediate form, the ovoviviparous animals: the embryo develops within and is nourished by an egg as in the oviparous case, but then it hatches inside the mother's body shortly before birth, or just after the egg leaves the mother's body. Some fish, reptiles and many invertebrates use this technique.
See also
External links
- description of 1800 genes involved in ovarian functions
