A chromosome is a thread-like structure of nucleic acids and protein found in the nucleus of most living cells, carrying genetic information in the form of genes. Each species has a fixed chromosome number. Gametes have half the number of chromosome. When they fuse, the original number is restored. At the time of fertilization male and female germ cells are fused to form a zygote. Therefore, the chromosome number of sexually reproducing parents and their offsprings is the same.