Genes and gene families - Human Gene Evolution - page 140

orangutan and rhesus monkey have three haptoglobin genes, humans have two
( HP , HPR ; 16q22), whilst the spider monkey and cebus monkey have only one
(McEvoy and Maeda 1988). The apolipoprotein(a) ( LPA ; 6q27; Lawn et al .,
1997; Pesole et al ., 1994) gene probably also emerged during this time since its
presence has only been detected in humans, apes, and Old World monkeys.
The number of rhesus blood group antigen genes varies between primate
species, humans having two ( RHD , RHCE ; 1p34-p36.2), gorillas two, chim-
panzees three, whilst orangutan, gibbons and all Old World and New World mon-
keys possess only a single RH -like gene (Salvignol et al ., 1995). Duplication of the
RH -like genes probably therefore occurred between 8 and 11 Myrs ago before
divergence of the human and gorilla lineages.
Eosinophil-derived neurotoxin (EDN) and eosinophil cationic protein (ECP) are
host defense proteins which are members of the ribonuclease family. They are
encoded respectively by the RNASE2 and RNASE3 genes located on human chro-
mosome 14q24-q31. Divergence of the nucleotide sequences of the two related genes
was found to be consistent with a duplication event occurring some 25-40 Myrs ago
after the divergence of Old World monkeys from New World monkeys (Hamann et
al ., 1990). In agreement with this prediction, RNASE2 and RNASE3 orthologues
are evident in chimpanzee, gorilla, orangutan and macaque but not in the marmoset,
a New World monkey (Rosenberg et al ., 1995; Zhang et al ., 1998). Since their dupli-
cation, the two proteins have diverged very rapidly, with evolution promoting the
acquisition of novel functions viz. increased cationicity/toxicity (ECP) and enhanced
ribonuclease activity (Rosenberg and Dyer, 1995).

4.1.3 Human genes which originated during primate evolution

The ZNF91 Kruppel-associated box-containing zinc finger gene family on
human chromosome 19p12-p13 is present in the great apes, the gibbons, Old
World and New World monkeys but is not found in prosimians or rodents
(Bellefroid et al ., 1995). The origin of this gene family is unclear. Presumably, the
ZNF91 gene cluster arose by duplication/amplification at least 55 Myrs ago in the
common ancestor of simians.
The three alcohol dehydrogenase genes ( ADH1 , ADH2, and ADH3 ), linked on
human chromosome 4q22, also originated during the adaptive radiation of the
primates; two successive duplications are estimated to have occurred 45±8 Myrs
and 60±8 Myrs ago (Duester et al ., 1986; Ikuta et al ., 1986; Trezise et al ., 1989;
1991; Yokoyama et al ., 1987).
Other examples of human genes with a primate origin include the interferon-

α
gene ( IFNA ) and growth hormone ( GH ) gene clusters. The IFNA cluster, con-
taining 13 members (see Section 4.2.1) and located at chromosome 9p21, has
emerged by a process of duplication and divergence over the last 26 Myrs (Miyata
and Hayashida 1982). The GH gene cluster is also essentially a primate creation
with several genes ( GH1 , GH2 , CSH1, and CSH2 ; 17q23) having emerged over
the last 25-50 Myrs by a process of duplication and divergence (Chen et al ., 1989;
Golos et al ., 1993; Miller and Eberhardt 1983). see Section 4.2.1).
Some genes emerged in the last 100 Myrs during the adaptive radiation of the
mammals. For example, the fucosyltransferase gene family ( FUT1 , FUT2 ,