Life begins in the moment of conception – the time when a reproductive cell of the female (ovum, plural ova.) is fertilized by a male reproductive cell the spermatozoon (spermatozoa, plural). This is approximately 280 days before birth.
Within each sex cell (sperm/egg) there are 23 chromosomes. They are threadlike particles which contains between 40,000 and 60,000 genes. The genes contain DNA and RNA which are considered as the blueprint of life and transmitters of hereditary characteristics traits from the parent to the offspring.
Sex Determination
All the female gametes carry X chromosomes, while half of the male gametes carry the X chromosomes and the other half carry the Y chromosomes.
If the X bearing spermatozoon unites with the ovum, it will result to XX combination and the sex of the child is female. And if the Y bearing spermatozoon unites with the ovum, it will result to XY combination and the sex of the sex child is male.
Multiple Birth/Twins
The term multiple births refer to the birth of two or more babies within a few hours or days. There are two types of twin births – the identical and fraternal twins. The identical or uniovular twins come from a single ovum fertilized by a single sperm cell.
Sometimes, it happens that at a time of the first division of the cell the new cell separates instead of remaining together. Why the separation occurs, no one knows for certain, but there are evidence that it is a result of hormonal disturbances.
Non-identical, biovular or fraternal twins on the other hand, are the products of two ova fertilized simultaneously by two separate sperm cells.
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