<Li> FOXD . The forkhead box D4 - like gene is an example of an intronless gene . The function of this gene is not known, but it may code for a transcription control protein . </Li> <Li> CBWD . Cobalamin synthetase is a bacterial enzyme that makes vitamin B. In the distant past, a common ancestor to mice and apes incorporated a copy of a cobalamin synthetase gene (see: Horizontal gene transfer). Humans are unusual in that they have several copies of cobalamin synthetase - like genes, including the one on chromosome 2 . It remains to be determined what the function of these human cobalamin synthetase - like genes is . If these genes are involved in vitamin B metabolism, this could be relevant to human evolution . A major change in human development is greater post-natal brain growth than is observed in other apes . Vitamin B is important for brain development, and vitamin B deficiency during brain development results in severe neurological defects in human children . </Li> <Li> CXYorf1 - like protein . Several transcripts of unknown function corresponding to this region have been isolated . This region is also present in the closely related chromosome 9p terminal region that contains copies of the PGML / FOXD / CBWD genes . </Li> <Li> Many ribosomal protein L23a pseudogenes are scattered through the human genome . </Li>

How many chromosomes do chimpanzees and gorillas have