Chromosomes are the small threadlike structure of nucleic acids and proteins found in the nucleus of most living cells that transmits genetic information in the form of genes.
This genetic information is stored in 23 pairs of chromosomes, making it 46 altogether. The 23rd pair is made up of two XX chromosomes in females and one X and one Y chromosome in a male. This means men have 46 chromosomes with the last pair being X and Y (chromosomes 46, XY), and women have 46 chromosomes, with the last two pairs being XX (chromosomes 46, XX).
Chromosomes always come in pairs in a normal healthy individual. One pair from the mother and the other pair from the father making up 46 chromosomes altogether.
Chromosomes determine how the human body and every organ develops as it grows in the uterus and how it continues to evolve after birth.
Anything that causes the chromosomes to be less than 46 or create a replica of an extra copy or loss a part of its structure (such as a deletion) changes how the baby develops and leads to several deficiencies.