Chromosome Defects: what are they?
There are 22 pairs of chromosomes, numbered 1-22 in order of size, and a pair of sex chromosomes, XX in females and XY in males, making a total of 46 chromosomes in each normal human cell. One X chromosome is inherited from the mother, and the other sex chromosome inherited from the father is either X (baby girl) or Y (baby boy) and determines, the sex of the child. Each chromosome can be considered as consisting of a long tightly packed string of genes.
The Human Egg and Sperm Cell
The human egg cell and the human sperm cell each contain only 23 chromosomes. When the egg is produced by the mother, the pairs of chromosomes in the egg cell split into two, and only one of each pair remains in the egg. The same happens with the sperm cell. When a healthy egg is fertilised by a healthy sperm, the fertilised egg has 46 chromosomes and is the unique blueprint for the individual baby that grows.
Karyotypes
A Karyotype or picture of chromosomes is prepared from a sample of blood, skin, bone marrow or connective tissue. The cultures are grown and the thread-like chromosomes in the cell are released on a slide and stained with dyes before being photographed and arranged in order of size to make study possible.