The chromosome complement of four species phylogenetically
related to man, the chimpanzee (Pan troglodytes), the pygmy
chimpanzee (Pan paniscus), the gorilla (Gorilla gorilla), and
the orangutan (Pongo pygmaeus) have been analysed with chromosome
banding techniques and compared to the human chromosome comple¬
ment. This has shown remarkable homologies between species,
and presumed mechanisms of chromosome evolution have been
proposed. Chromosome heteromorphisms in the great apes have
been compared to those found in human populations, and most of
them affected the distribution or the amount of constitutive heterochromatin
and/or brilliantly fluorescent material, a situation
comparable to man where such variations have been established as
chromosome polymorphisms. However, a balanced polymorphic structural rearrangement involving large segments of euchromatic
material has been found in two populations of orangutan. This
rearrangement consisted of two pericentric inversions, one inside
the other, comprising an unusual kind of chromosome polymorphism in
mammalian populations. Moreover, it showed that pericentric
inversions, the most probable chromosome rearrangements in the
phylogeny of the chromosomes of man and the great apes, might not
necessarily be restricted by infertility barriers, but may spread
successfully in the population. The patterns of late replication of the chromosomes of the
great apes and man have been compared, using BUdr as a thymidine
substitute in the cell cycle. This has shown remarkable similarities
in the patterns of late replication between species, and, as in the human chromosomes, most regions of late replication in the
chromosomes of the great apes corresponded to areas of positive
G-banding. Q-, C- and G-banding as methods of demonstrating
chromosome homologies between these species have been analysed
in relation to the content of highly repeated satellite DNAs in man
and homologous sequences in the great apes. This has shown that
the banding patterns are not informative about these sequences,
and that they must reflect a degree of chromosome organization due
to DNA packaging rather than DNA composition. Finally, the
phylogeny of the chromosomes of man and the great apes has been
reconstructed in view of the findings presented in this work and of
previous data in the literature. In this study, man and gorilla
resembled each other more closely than to any of the other species
studied, a finding that is contrary to the generally held view that
man and the chimpanzee are the two most closely related species. Comparative studies of the spermatozoa of the great apes and
man were undertaken and showed that man was not unique in producing
pleiomorphic spermatozoa, since this feature was also present in
the gorilla. Moreover, the morphology of human and gorilla
spermatozoa resembled each other so closely that on morphological
grounds it was impossible to distinguish the spermiogram of these
two species. Fluorescent ("f") bodies were detected in the
spermatozoa of the African apes, although the distribution of such
bodies did not resemble that of human spermatozoa, where the Y
chromosome is usually visible. An analysis of the haploid DNA
content of the great apes and man w®3 undertaken by estimating the
total dry mass of the sperm head in these species. Man showed the
lowest DNA content, whilst the gorilla showed the highest; this
latter latter species also showed a higher variability in the haploid
DNA content than all other species, including man. Diploid
spermatozoa were also detected in the gorilla, in proportions
similar to those found in man. These findings on spermatozoa
are indicative of a closer relationship between man and gorilla
than between man and the other hominoid apes. Moreover, the
heteromorphism of spermatozoa in both human and gorilla semen
samples makes it unlikely that clothing induced hyperthermia is
the cause of pleiomorphic spermatozoa in man
