Chromosome tests are normal, genes can be problematic. Chromosomes are the carriers of genes, and chromosomes only look at problems with the structure and quantity of genetic material, etc., while genes look at whether there are problems with the expression of specific genes on the chromosomes. Genes are prone to base mismatches during replication, and once they occur at the chromosome level it may not be easy to detect the problem, but gene expression will be affected. Generally speaking chromosomes are important substances in cells carrying biological genetic information, in the human body somatic cells chromosomes are distributed in pairs, called diploid. Sex cells, such as sperm and eggs, are haploid, and the number of chromosomes is only half that of somatic cells. Genes are genetic information carried by chromosomes that determine the basic constitution and performance of life. Therefore, if chromosomes are a whole, genes are the components of chromosomes, and there are commonalities but also differences in their effects on phenotype. Chromosomes may be fine from a macroscopic point of view, but may appear abnormal from the detailed point of view of genes.