ABO and Rh Blood Types

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ABO and Rh Blood Types May 16, 2023 18:22:16 GMT

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Post by Admin on May 16, 2023 18:22:16 GMT

Blood groups in ancient Europe

Human blood groups are interesting from both medical and evolutionary perspectives. Different blood groups confer resistance or susceptibility to a wide range of infectious disease and, likely as a result of this, have been under long-term balancing selection across primates. They also vary dramatically in frequency across human populations and, probably, across time as well. Here, we use ancient DNA to estimate the frequencies of the two most commonly discussed groups - specifically the ABO and Rhesus systems - in Europe over the past ten thousand years. We show that some ancient populations of Europe had blood group frequencies that were more extreme than any present-day population. In particular, Mesolithic hunter-gatherers had a higher frequency of type O than any present-day population, and both hunter-gatherers and bronze-age steppe populations had a higher frequency of the Rhesus negative allele than any present-day population.

ABO
The ABO blood group system was the earliest to be discovered. ABO blood group is determined by polymorphisms in the ABO gene. In particular, the type O allele is determined by a 1 base deletion (rs8176719) and if that deletion is not present then type A and B are determined by the SNPs rs8176746 and rs8176747. Actually it is more common than that, for example there are many other loss-of-function mutations that lead to the O phenotype, but these are relatively rare.

In evolutionary sense, types A and B are the oldest, since those polymorphisms are shared with other primates. The human type O allele is a more recent mutation, but still probably at least one million years old (the Altai Neanderthal is type O, for example). In present-day populations, all three alleles segregate in Africa, A/O are most common in Europe with B~5-10%, B is relatively common in Asia, but O is virtually fixed in Native Americans.

Rhesus
The Rhesus blood group system is the second most commonly encountered system, determined by polymorphism at the RHD gene. Again, this system has a large number of different groups, but the most important is the Rh- group, where the gene is completely inactivated. In Europe, the most common such allele is actually a deletion at chr1:25592642-25661222, which completely deletes RHD. This polymorphism is at around 10-20% frequency in African populations, very rare in East Asia, and relatively common (~40%) in Europe. The allele is recessive, so you need two copies of the Rh- allele to have the Rh- phenotype.

This high frequency in Europe has long been surprising because the Rh- phenotype has an obviously deleterious effect. In particular, if an Rh- mother has an Rh+ child (because the child inherited a Rh+ allele from its father), then it’s possible for the mother to produce antibodies against the Rh+ antigen leading to haemolytic disease and severe illness for the child. There are three common explanations for the high frequency of the Rh- allele. First, there might be some (unknown) beneficial effect of the Rh-allele. Effects like this related to malaria resistance are what drive the high frequencies of the sickle cell trait and many thalassemias. On the other hand, no obvious selective advantage is known, there are no obvious genomic signals of selection on the Rh- allele, and if there were a selective advantage to the Rh- allele then we might ask why it hasn’t fixed, since once the Rh- frequency rose above 50%, it would be selected for, rather than against. So this only really works if it is overdominant. Another possible explanation is reproductive overcompensation - Rh- women have more children to replace the ones that die for haemolytic disease. But this seems unlikely. The range of parameters for which this model works is relatively small, particularly since the effect gets worse for subsequent pregnancies. A third explanation, suggested by Haldane in 1942 is that the high frequency in Europe is due to the fact that present-day Europeans are recently admixed between a population that has a very high frequency of the Rh- allele and one that a very low frequency. In fact, the ancient DNA evidence suggests that something like this is close to the truth. Cavalli-Sforza and colleagues thought that this was specifically a mixture between Rh- hunter-gatherers and Rh+ Farmers, largely based on the observation that the Basque population, who they believed to have largely hunter-gatherer ancestry, have a very high frequency of the Rh- phenotype.

Ancient DNA
I looked at these alleles in ancient samples dating to the past 12,000 years, all from West Eurasia. I divided them into four groups:

Hunter-gatherers (HG); Mesolithic and neolithic individuals with ancestry that is like that of Mesolithic Europeans.
Early Farmers (EF); Neolithic individuals from NW Anatolia, and European Neolithic individuals with similar ancestry, plus small (~0-20%) amounts of hunter-gatherer ancestry.
Steppe (ST); Bronze Age individuals with “Yamnaya-like” ancestry
Bronze Age (BA); Individuals from Bronze Age Europe that have a mixture of the three other types of ancient ancestry.
I also compared with present-day European populations, separating out Finns (FIN) and Non-Finns (NFE) (Finns have more steppe-like ancestry).

The ABO determining variants are on the 1240k capture array that has been used to genotype many samples, so I was able to look them up in a sample of around ~500 ancient individuals (the same individuals used here). I looked up present-day allele frequencies in gnomAD. It’s harder to genotype the RHD deletion from capture data so I used a smaller dataset of around ~200 individuals with published shotgun data to genotype this deletion. I couldn’t find it in gnomAD so I used allele frequencies from 1000 Genomes.

It turns out that the O allele is at high frequency in hunter-gatherers, but relatively rare on the Steppe. The B allele seems to be absent in both hunter-gatherers and early farmers, and seems to be introduced from the steppe in the Bronze Age. The Rh- allele seems to be relatively common in hunter-gatherers and, particularly, in steppe populations, and relatively rare in early farmers, partly confirming Haldane and Cavalli-Sforza’s hypotheses. Allele frequency estimates are in the figures below (bars show 95% binomial confidence intervals).

Broadly speaking, the present-day frequencies are consistent with genome-wide ancestry, in the sense that they are just a mixture of the ancient populations (roughly equal to the Bronze Age). The Rh- frequency in present-day Europe is a bit lower than in the Bronze Age, which might be evidence for selection against the allele, but might also just be because there’s a bit less Steppe ancestry in 1000 Genomes than in the samples Bronze Age populations. This doesn’t really explain the Basque frequency though. The Basque population doesn’t particularly have a lot of hunter-gatherer or Steppe ancestry. But perhaps there is substructure in Rh- frequencies within the Basque population, or within the hunter-gatherer populations. Finally, we’ve explained the present-day frequency in terms of mixtures of ancestral populations, but really we have just pushed the question back ten thousand years. Why was the Rh- frequency so high in hunter-gatherer and Steppe populations? Clearly there has to be some selective advantage to this allele at some point, otherwise it would just have been removed everywhere. Perhaps in these populations that selective advantage was stronger. Or perhaps they were just sufficiently small that it was able to drift to high frequency.

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ABO and Rh Blood Types May 16, 2023 19:11:53 GMT

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Post by Admin on May 16, 2023 19:11:53 GMT

Blood group analyses for three Neanderthals and one Denisovan by a team from the Anthropologie Bio-Culturelle, Droit, Éthique et Santé research unit (CNRS / Aix-Marseille University / EFS) confirm hypotheses concerning their African origin, Eurasian dispersal, and interbreeding with early Homo sapiens. The researchers also found further evidence of low genetic diversity and possible demographic fragility. Their findings are published in PLOS ONE (28 July 2021).

The extinct hominin lineages of the Neanderthals and Denisovans were present throughout Eurasia from 300,000 to 40,000 years ago. Despite prior sequencing of about 15 Neanderthal and Denisovan individuals, the study of the genes underlying blood groups had hitherto been neglected. Yet blood group systems were the first markers used by anthropologists to reconstruct the origins of hominin populations, their migrations, and their interbreeding.

In a new study, scientists from the CNRS, Aix-Marseille University, and the French Blood Establishment (EFS) have examined the previously sequenced genomes of one Denisovan and three Neanderthal females who lived 100,000 to 40,000 years ago, in order to identify their blood groups and consider what they may reveal about human's evolutionary history. Of the 40-some known blood group systems, the team concentrated on the seven usually considered for blood transfusion purposes, the most common of which are the ABO (determining the A, B, AB, and O blood types) and Rh systems.

The findings bolster previous hypotheses but also offer new surprises. While it was long thought that Neanderthals were all type O -- just as chimpanzees are all type A and gorillas all type B -- the researchers demonstrated that these ancient hominins already displayed the full range of ABO variability observed in modern humans. Extensive analysis covering other blood group systems turned up alleles that argue in favour of African origins for Neanderthals and Denisovans.

Especially surprising is the discovery that the Neanderthals harboured a unique Rh allele absent in modern humans -- with the notable exceptions of one Aboriginal Australian and one Papuan. Do these two individuals bear testimony to interbreeding of Neanderthals and modern humans before the migration of the latter into Southeast Asia?

Finally, this study sheds light on Neanderthal demographics. It confirms that these ancient hominins exhibited very little genetic diversity, and that they may have been susceptible to haemolytic disease of the fetus and newborn (erythroblastosis fetalis) -- due to maternofetal Rh incompatibility -- in cases where Neanderthal mothers were carrying the children of Homo sapiens or Denisovan mates. These clues strengthen the hypothesis that low genetic diversity together with low reproductive success contributed to the disappearance of Neanderthals.

Silvana Condemi, Stéphane Mazières, Pierre Faux, Caroline Costedoat, Andres Ruiz-Linares, Pascal Bailly, Jacques Chiaroni. Blood groups of Neandertals and Denisova decrypted. PLOS ONE, 2021; 16 (7): e0254175 DOI: 10.1371/journal.pone.0254175

journals.plos.org/plosone/article?id=10.1371/journal.pone.0254175

Blood groups of Neandertals and Denisova decrypted

RH system. All of the backgrounds are based on the Dce (R0) haplotype as described in Africa [8] and we found only one complete Dce (R0) haplotype corresponding to the wild type described in modern human populations [8]. This complete R0 haplotype is present, at a single dose, in the Denisova-3 sample. The other haplotypes are variants encoding partial antigens D, c and e, which are missing some epitopes. All of these haplotypes, whether wild or variant, are related, phylogenetically speaking, to the African RHD*DIVa cluster [8]. From the three Neanderthal genomes, we have identified one potential novel RHD variant sharing typical SNP combinations assigned to this cluster (Fig 2). This variant exhibited the three SNPs that characterize the partial RHD*DIII type4 (or RHD*03.04 defined by c.186T, c.410T and c.455C), combined with two additional SNPs, c.602C>G and c.733G>C. This latter SNP defining the partial RHD*DUC2 allele. This new combination has been reported for the first time in only one modern Australian Aborigine [29] and occurred at a homozygous level in Altaï, and at least at a heterozygous level in Vindija and Chagyrskaya, with a normal RHD Exon-9 sequence (c.1170T, c.1193A) for all of them. This new RHD variants segregated with RHCE*ce allele variants although the RHD*DIII type4 has been reported to segregate with RHCE*Ce in modern humans [30].

Furthermore, we found the presence of at least three RHCE*ceEK variant alleles (c.48G>C, c.712A>G, c.787A>G and possibly c.800T>A) in Altai Neandertal, Vindija and Chagyrskaya, and two wild-type RHCE*ce in Denisova-3. Each of the Neanderthal archaic genomes has one other African RHCE*ce variant in cis. The RHCE*ceEK allele is mostly encountered in people of African descent [31]. When present in double dose, it encodes a rare phenotype defined by the absence of public antigen RH:-18. The anti-RH18 antibody has been reported to be responsible for haemolytic transfusion reactions and haemolytic disease of the foetus and new-born (HDFN) [32].

www.ncbi.nlm.nih.gov/pmc/articles/PMC8318287/

Last Edit: Jun 30, 2023 21:08:02 GMT by Admin

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ABO and Rh Blood Types May 16, 2023 19:44:58 GMT

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Post by Admin on May 16, 2023 19:44:58 GMT

Worse Health Status and Higher Incidence of Health Disorders in Rhesus Negative Subjects

Abstract
Rhesus-positive and Rhesus-negative persons differ in the presence-absence of highly immunogenic RhD protein on the erythrocyte membrane. The biological function of the RhD molecule is unknown. Its structure suggests that the molecular complex with RhD protein transports NH3 or CO2 molecules across the erythrocyte cell membrane. Some data indicate that RhD positive and RhD negative subjects differ in their tolerance to certain biological factors, including, Toxoplasma infection, aging and fatique. Present cross sectional study performed on 3,130 subjects) showed that Rhesus negative subjects differed in many indices of their health status, including incidences of many disorders. Rhesus negative subjects reported to have more frequent allergic, digestive, heart, hematological, immunity, mental health, and neurological problems. On the population level, a Rhesus-negativity-associated burden could be compensated for, for example, by the heterozygote advantage, but for Rhesus negative subjects this burden represents a serious problem.

Introduction
Polymorphism in the Rhesus factor, namely the existence of a large deletion in the RHD gene [1] in a substantial fraction of the human population, has been an evolutionary enigma since the discovery of this factor in the 1930’s [2–5]. Theoretically, neither the RhD-negative allele can successfully spread in the RhD positive population nor the RhD-positive allele can spread in the RhD negative population [6,7]. Before the introduction of prophylactic treatment in 1968, a positive frequency dependent selection systematically penalized the less abundant allele because lots of children of RhD-negative women in the mostly RhD-positive population as well as children of RhD- positive men in the mostly RhD-positive population were dying of hemolytic anemia. It has been suggested that this polymorphism can be stabilized when the disadvantage of carriers of the locally rarer allele is counterbalanced by higher viability of their heterozygote children or by another form of frequency-dependent selection [6]. In the past seven years, several studies have demonstrated that Rhesus positive and Rhesus negative subjects differ in resistance to the adverse effects of parasitic infections, aging, fatigue and smoking [7–13]. A study performed on 250 blood donors has further shown that the resistance to effects of toxoplasmosis is higher in Rhesus positive heterozygotes than in Rhesus positive homozygotes and substantially higher than in Rhesus negative homozogotes [7]. This is the first direct evidence for the role of selection in favour of heterozygotes in stabilization of the RHD gene polymorphism in human populations. Such a mechanism is reminiscent of widely known situations with polymorphism in genes associated with sickle cell anaemia in geographic regions with endemic malaria [14].

The results of previous studies suggest that RhD negative homozygotes could have a worse health status than RhD positive population consisting of RhD positive homozygotes and heterozygotes. These results, however, were obtained on either rather small or rather specific populations, e.g. military personnel [13] or pregnant women [12]. To obtain more reliable data about situation in more typical populations, we run a large questionnaire study in a population of healthy Czech and Slovak volunteers. Using an electronic questionnaire distributed with a Facebook-based snowball method [15], we have screened a population of 3,130 subjects for indices of various health problems as well as for incidences of 225 diseases and disorders.

www.ncbi.nlm.nih.gov/pmc/articles/PMC4619848/

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ABO and Rh Blood Types May 17, 2023 0:11:27 GMT

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Post by Admin on May 17, 2023 0:11:27 GMT

Evolutionary genetics of the human Rh blood group system

Abstract
The evolutionary history of variation in the human Rh blood group system, determined by variants in the RHD and RHCE genes, has long been an unresolved puzzle in human genetics. Prior to medical treatments and interventions developed in the last century, the D-positive children of D-negative women were at risk for hemolytic disease of the newborn, if the mother produced anti-D antibodies following sensitization to the blood of a previous D-positive child. Given the deleterious fitness consequences of this disease, the appreciable frequencies in European populations of the responsible RHD gene deletion variant (for example, 0.43 in our study) seem surprising. In this study, we used new molecular and genomic data generated from four HapMap population samples to test the idea that positive selection for an as-of-yet unknown fitness benefit of the RHD deletion may have offset the otherwise negative fitness effects of hemolytic disease of the newborn. We found no evidence that positive natural selection affected the frequency of the RHD deletion. Thus, the initial rise to intermediate frequency of the RHD deletion in European populations may simply be explained by genetic drift/ founder effect, or by an older or more complex sweep that we are insufficiently powered to detect. However, our simulations recapitulate previous findings that selection on the RHD deletion is frequency dependent, and weak or absent near 0.5. Therefore, once such a frequency was achieved, it could have been maintained by a relatively small amount of genetic drift. We unexpectedly observed evidence for positive selection on the C allele of RHCE in non-African populations (on chromosomes with intact copies of the RHD gene) in the form of an unusually high FST value and the high frequency of a single haplotype carrying the C allele. RhCE function is not well understood, but the C/c antigenic variant is clinically relevant and can result in hemolytic disease of the newborn, albeit much less commonly and severely than that related to the D-negative blood type. Therefore, the potential fitness benefits of the RHCE C allele are currently unknown but merit further exploration.

Keywords: Blood group polymorphism, copy number variation, human evolution, balancing selection

INTRODUCTION
The human Rh blood group system is a collection of antigens expressed on erythrocyte cell membranes (Avent and Reid 2000) that may play a role in the transport of ammonia (Marini et al. 2000) or carbon dioxide (Endeward et al. 2008; Kustu and Inwood 2006), or not in transport but in erythrocyte membrane structure (Westhoff 2004; Westhoff and Wylie 2006). Functional (antigen) variation in the Rh blood group system is determined by insertions/ deletions, single nucleotide polymorphisms (SNPs), and gene conversion events in the RHD and RHCE genes (Colin et al. 1991; Flegel 2011; Mouro et al. 1993). Homozygous deletion of the entire RHD gene results in the D-negative blood phenotype (Wagner and Flegel 2000), whereas the D-positive phenotype is conferred by the presence of either one or two intact copies of the RHD gene.

D-negative mothers may produce anti-D antibodies following exposure to red blood cells from a D-positive fetus during pregnancy or childbirth. Subsequent D-positive offspring of a D-negative mother may develop hemolytic disease of the newborn resulting in fetal death or severe disability (Levine et al. 1941; Urbaniak and Greiss 2000). Prior to treatments introduced beginning in the 1940s (culminating with Rho(D) Immune Globulin (RhoGAM) in 1968) that largely obviated these health issues (Urbaniak and Greiss 2000), D-negative mothers may have suffered reduced reproductive fitness; pre-treatment mortality from hemolytic disease of the newborn was reportedly 1 in every 56 births to D-negative women in a European-American population (1 in 392 births among all women, regardless of D status) (Potter 1947). Certain non-synonymous SNPs in the RHCE gene result in antigenic variation in the encoded RHCE protein (rs676785, Ser103Pro: C/c; rs609320, Pro226Ala: E/e) (Avent and Reid 2000), and differential expression of these antigens can also lead to hemolytic disease of the newborn, but with much lower frequency than that caused by anti-D antibodies, at least in European populations (Moncharmont et al. 1991).

Based on the potential consequence of hemolytic disease of the newborn, one might expect strong purifying selection to have acted against the D-negative phenotype and minor alleles of the C/c and E/e antigens. Yet in European populations the D-negative phenotype is observed at substantial frequencies, typically 0.15-0.17 and up to 0.29 in the Basque (Touinssi et al. 2004; Urbaniak and Greiss 2000), and the frequency of the RHCE C allele is ~0.44 (Urbaniak and Greiss 2000). Similar to the effects of sickle cell and thalassemia hemoglobin heterozygosity on malarial resistance (Allen et al. 1997; Allison 1954; Flint et al. 1986; Kwiatkowski 2005), we asked whether these alleles confer an unknown fitness benefit whereby positive or balancing selection explains their otherwise surprisingly high frequencies (Feldman et al. 1969; Westhoff 2004). Because such a history may have left detectable genomic signatures, in this study we used a population genetics framework to test evolutionary hypotheses concerning these functional genetic variants of the Rh blood group system.

www.ncbi.nlm.nih.gov/pmc/articles/PMC3378649/

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ABO and Rh Blood Types May 17, 2023 3:12:33 GMT

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Post by Admin on May 17, 2023 3:12:33 GMT

Rh Gene Evolution in Primates: Study of Intron Sequences
Pol-André Apoil, Antoine Blancher

Abstract
By amplification and sequencing of RH gene intron 4 of various primates we demonstrate that an Alu-Sx-like element has been inserted in the RH gene of the common ancestor of humans, apes, Old World monkeys, and New World monkeys. The study of mouse and lemur intron 4 sequences allowed us to precisely define the insertion point of the Alu-Sx element in intron 4 of the RH gene ancestor common to Anthropoidea. Like humans, chimpanzees and gorillas possess two types of RH intron 4, characterized by the presence (human RHCE and ape RHCE-like genes) or absence (human RHD and ape RHD-like genes) of the Alu-Sx element. This led us to conclude that in the RH common ancestor of humans, chimpanzees, and gorillas, a duplication of the common ancestor gene gave rise to two genes, one differing from the other by a 654-bp deletion encompassing an Alu-Sx element. Moreover, most of chimpanzees and some gorillas possess two types of RHD-like intron 4. The introns 4 of type 1 have a length similar to that of human RHD intron 4, whereas introns 4 of type 2 display an insertion of 12 bp. The latest insertion was not found in the human genome (72 individuals tested). The study of RH intron 3 length polymorphism confirmed that, like humans, chimpanzees and gorillas possess two types of intron 3, with the RHD-type intron 3 being 289 bases shorter than the RHCE intron 3. By amplification and sequencing of regions encompassing introns 3 and 4, we demonstrated that chimpanzee and gorilla RH-like genes displayed associations of introns 3 and 4 distinct to those found in man. Altogether, the results demonstrate that, as in humans, chimpanzee and gorilla RH genes experienced intergenic exchanges.

Introduction
The human RH blood group system, one of the most polymorphic in humans, is of utmost clinical importance because of the high immunogenicity of its antigens, particularly antigens D and c. Antibodies against Rh antigens are responsible for transfusion accidents and for most of fetomaternal incompatibilities (Mollison 1979 ). Ten years ago, it was demonstrated that humans possess two RH genes that are closely linked on chromosome 1: RHD, which encodes the D polypeptide and is present or absent depending on the RH haplotype (Colin et al. 1991 ), and RHCE, which displays four common alleles responsible for the expression of the two allelic series of antigens C/c and E/e (Mouro et al. 1993 ). In a double dose, the complete deletion of RHD is responsible in Caucasians for the D-negative phenotype (Colin et al. 1991 ). In other populations (Africans, Japanese), D-negative individuals frequently possess in double-dose nonfunctional RHD genes which are wholly or partially deleted (Blunt, Daniels, and Carritt 1994 ; Hyland, Wolter, and Saul 1994; Daniels, Green, and Smart 1997 ; Okuda et al. 1997 ; Sun et al. 1998 ). RHCE and RHD are highly homologous and most probably derived by duplication from a common ancestor gene (Colin et al. 1991 ; Le Van Kim et al. 1992 ). This homology between RHD and RHCE probably promoted genetic exchanges between the two genes. This was demonstrated by the characterization at the genomic level of RHD genes which encode qualitative variants of the antigen D: most of these antigenic variants are encoded by low-frequency RHD alleles which display replacement of some exons by their RHCE counterparts. These replacements can be due to various mechanisms of intergenic exchange (double crossing over or gene conversion) (for a general review, see Huang 1997a ). Moreover, it was demonstrated that the four main alleles of the RHCE gene derived through intergenic exchanges and interallele recombinations from a few ancestor alleles (Carritt, Kemp, and Poulter 1997 ). Particularly, in humans, one gene exchange, consisting of the replacement of RHCE exon 2 by its RHD counterpart, led to the appearance of RHCE alleles coding for the C antigen (Carritt, Kemp, and Poulter 1997 ).

Nonhuman primates express counterparts of the human Rh antigens (Masouredis, Dupuy, and Elliot 1967 ; Moor-Jankowski and Wiener 1972 ). The use of monoclonal antibodies confirmed that chimpanzees and gorillas express polymorphic antigens, namely chimpanzee Rc and gorilla Dgor, which share epitopes with the human D antigen (Socha and Ruffié 1990 ; Blancher, Calvas, and Ruffié 1992 ). The expression of antigens Rc and Dgor was shown to depend on RH-like genes of chimpanzees and gorillas, respectively (Salvignol et al. 1993, 1994 ; Blancher and Socha 1997 ). Gibbons and orangutans also express D-like antigens, but the small number of animals studied did not allow the description of a polymorphism in these species (Blancher and Socha 1997 ). It has to be noted that if the expression of Rh-like antigens seems to be restricted to apes, the presence of Rh-like polypeptides at the surfaces of RBCs of Old World monkeys, New World monkeys, lemurs, and many other mammalians (cats, dogs, bovines, rats, mice) was evidenced by biochemical techniques (Saboori, Denker, and Agre 1989 ) or by immunoblotting (Mouro et al. 1994 ; Salvignol et al. 1995 ; Apoil and Blancher 1999 ). Despite their conservation throughout evolution, the function of Rh polypeptides remains elusive.

Southern blot studies demonstrated that only humans and African apes (chimpanzees and gorillas) possess more than one gene per haploid genome (Salvignol et al. 1993 ; Westhoff and Wylie 1994 ; Blancher and Socha 1997 ). Chimpanzees and gorillas possess at least three and two RH-like genes, respectively (Blancher and Socha 1997 ). Thus, it was deduced that the duplication event which led to the appearance of the RHCE and RHD genes arose most probably in the common ancestor species of humans, chimpanzees, and gorillas.

The two human RH genes differ in their coding sequences, but also in their noncoding elements, including length polymorphisms of intron 3 (Matassi et al. 1997 ) and intron 4 (Arce et al. 1993 ). Intron 4 of the RHCE gene differs from intron 4 of the RHD gene in the presence of a 654-bp fragment which encompasses an Alu-Sx element (Westhoff and Wylie 1996 ; Huang 1997b; Okuda et al. 1997 ). Like humans, gorilla possesses introns 3 and 4 length polymorphisms which are counterparts of the RHD/RHCE intronic polymorphisms observed in humans (Westhoff and Wylie 1996 ; Apoil, Roubinet, and Blancher 1999 ). For example, some gorillas RH-like genes exhibit RHCE-like introns 4 which harbor an Alu-Sx element orthologous to the Alu in human RHCE intron 4 (Apoil, Roubinet, and Blancher 1999 ). It was not possible from previous results to determine whether the Alu insertion in the RHCE gene arose after the duplication of a common ancestor gene or whether the RHD ancestor gene lost a 654-bp fragment. Results presented here are in good agreement with the deletion hypothesis.

Although chimpanzees and gorillas possess more than one gene per haploid genome (Blancher, Calvas, and Ruffié 1992 ), comparative studies of chimpanzee and gorilla RH-like cDNAs did not bring a definitive demonstration that genetic exchanges have occurred between RH-like genes in these species (Salvignol et al. 1995 ; Apoil and Blancher 1999 ). With the aim of demonstrating such intergenic exchanges, we decided to study noncoding parts of chimpanzee and gorilla RH-like genes.

academic.oup.com/mbe/article/17/1/127/975586?login=false