Archaic admixture has had a substantial impact on human evolution with multiple events across different clades, including from extinct hominins such as Neanderthals and Denisovans into modern humans. In great apes, archaic admixture has been identified in chimpanzees and bonobos but the possibility of such events has not been explored in other species. Here, we address this question using high-coverage whole-genome sequences from all four extant gorilla subspecies, including six newly sequenced eastern gorillas from previously unsampled geographic regions. Using approximate Bayesian computation with neural networks to model the demographic history of gorillas, we find a signature of admixture from an archaic 'ghost' lineage into the common ancestor of eastern gorillas but not western gorillas. We infer that up to 3% of the genome of these individuals is introgressed from an archaic lineage that diverged more than 3 million years ago from the common ancestor of all extant gorillas. This introgression event took place before the split of mountain and eastern lowland gorillas, probably more than 40 thousand years ago and may have influenced perception of bitter taste in eastern gorillas. When comparing the introgression landscapes of gorillas, humans and bonobos, we find a consistent depletion of introgressed fragments on the X chromosome across these species. However, depletion in protein-coding content is not detectable in eastern gorillas, possibly as a consequence of stronger genetic drift in this species.
Phylogenetic relationships among 23 nonhuman primate (NHP) major histocompatibility complex class I chain-related gene (MIC) sequences, 54 confirmed human MICA alleles, and 16 human MICE alleles were constructed with methods of sequence analysis. Topology of the phylogenetic tree showed separation between NHP MICs and human MICs. For human MICs, the topology indicated monophyly for the MICB alleles, while MICA alleles were separated into two lineages, LI and LII. Of these, LI MICA alleles shared a common ancestry with gorilla (Ggo) MIC. One conservative amino acid difference and two nonconservative amino acid differences in the alpha3 domain were found between the MICA lineages. The nonconservative amino acid differences might imply structural and functional differences. Transmembrane (TM) trinucleotide-repeat variants were found to be specific to the MICA lineages such as A4, A9, and A10 to LI and A5 to LII. Variants such as A5.1 and A6 were commonly found in both MICA lineages. Based on these analyses, we postulate a polyphyletic origin for MICA alleles and their division into two lineages, LI and LII. As such, there would be 30 alleles in LI and 24 alleles in LII, thereby reducing the current level of polymorphism that exists, based on a presumed monophyletic origin. The lower degree of polymorphism in MICA would then be in line with the rest of the human major histocompatibility complex nonclassical class I genes.
Abductor pollicis longus (APL) muscle is known to exhibit different variations with respect to its attachments. Various studies have reported the splitting of the APL muscle. Comparative anatomical findings of split insertion of APL is commonly found in chimpanzees, gorillas and gibbons. In the present study, we describe an anomalous APL muscle, which originated from the posterior surface of the shaft of the radius and ulna and traversed a course deep to the extensor retinaculum. Interestingly, immediately after emerging form the deeper aspect of extensor retinaculum, the thin tendon of the APL muscle continued again as a muscular belly in relation to the dorsolateral part of the 1st metacarpal bone, to end as a tendon with its attachment to the base of the proximal phalanx. Such an unusual variation of APL with its attachment into proximal phalanx is a rare finding and may be of importance in altering the mechanics of the thumb during abduction. The clinical significance of such an anatomical variation of APL may be important during reconstructive surgeries involving thumb and also of academic interest.
Palmaris longus (PL) tendon is regularly used in reconstructive surgeries as a donor tendon because it is observed as an accessory muscle and has little practical use to the human hands. It is only found in mammals. For example, the orangutan has PL but it is absent variable in the higher class of apes such as gorillas and chimpanzees. The absence of PL in humans appears to be hereditary, but the genetic transmission is unclear. The main objective of this study is to determine the prevalence of PL tendon absence in pre-clinical medical students of UMS and to compare the lack between gender and ethnic groups. By using standard Schaffer’s test, we examined the presence or absence of PL tendon among the first and second-year medical students of UMS. Four additional tests, Thompson’s test, Mishra’s test I, and II, Pushpakumar’s tests were used to determine whether PL present or not. A total of 134 volunteers were examined, and 91.8% were right-handed, and 8.2% were left-handed. The overall absence (bilateral and unilateral) of PL tendon was 23.9%, whereas unilateral absent was 17.9%, and bilateral absent was 6.0%. The high prevalence of absence of PL tendon among females 25.5% compared to males 20.0%. Chinese and Indian have a higher incidence of PL tendon absence followed by Kadazandusun and Malay. In this study, there were different figures for each ethnic group. The prevalence of absence of PL varies depending on the populations.