chimpanzee genome. Genetics and genomics Relationships of bonobos to humans and other apes can be determined by comparing their genes or whole genomes. While the first bonobo genome was published in 2012, a high-quality reference genome became available only in 2021. The overall nucleotide divergence between chimpanzee and bonobo based on the latter is 0.421 ± 0.086% for autosomes and 0.311 ± 0.060% for the X chromosome. The reference genome predicts 22,366 full-length protein-coding genes and 9,066 noncoding genes, although cDNA sequencing confirmed only 20,478 protein-coding and 36,880 noncoding bonobo genes, similar to the number of genes annotated in the human genome. Overall, 206 and 1,576 protein-coding genes are part of gene families that contracted or expanded in the bonobo genome compared to the human genome, respectively, that is, these genes were lost or gained in the bonobo genome compared to humans. Description The bonobo is commonly considered to be more gracile than the common chimpanzee. Although large male chimpanzees can exceed any bonobo in bulk and weight, the two species broadly overlap in body size. Adult female bonobos are somewhat smaller than adult males. Body mass ranges from with an average weight of in males against an average of in females. The total length of bonobos (from the nose to the rump while on all fours) is . Male bonobos average when standing upright, compared to in females. The bonobo's head is relatively smaller than that of the common chimpanzee with less prominent brow ridges above the eyes. It has a black face with pink lips, small ears, wide nostrils, and long hair on its head that forms a parting. Females have slightly more prominent breasts, in contrast to the flat breasts of other female apes, although not so prominent as those of humans. The bonobo also has a slim upper body, narrow shoulders, thin neck, and long legs when compared to the common chimpanzee. Bonobos are both terrestrial and arboreal. Most ground locomotion is characterized by quadrupedal knuckle-walking. Bipedal walking has been recorded as less than 1% of terrestrial locomotion in the wild, a figure that decreased with habituation, while in captivity there is a wide variation. Bipedal walking in captivity, as a percentage of bipedal plus quadrupedal locomotion bouts, has been observed from 3.9% for spontaneous bouts to nearly 19% when abundant food is provided. These physical characteristics and its posture give the bonobo an appearance more