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One pedigree we all may have come from – did Adam and Eve have the chromosome 2 fusion?

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ABSTRACT

Background: In contrast to Great Apes, who have 48 chromosomes, modern humans and likely Neandertals and Denisovans have and had, respectively, 46 chromosomes. The reduction in chromosome number was caused by the head-to-head fusion of two ancestral chromosomes to form human chromosome 2 (HSA2) and may have contributed to the reproductive barrier with Great Apes.

Results: Next generation sequencing and molecular clock analyses estimated that this fusion arose prior to our last common ancestor with Neandertal and Denisovan hominins ~ 0.74 - 4.5 million years ago.

Hypotheses: I propose that, unlike recurrent Robertsonian translocations in humans, the HSA2 fusion was a single nonrecurrent event that spread through a small polygamous clan population bottleneck. Its heterozygous to homozygous conversion, fixation, and accumulation in the succeeding populations was likely facilitated by an evolutionary advantage through the genomic loss rather than deregulation of expression of the gene(s) flanking the HSA2 fusion site at 2q13.

Conclusions: The origin of HSA2 might have been a critical evolutionary event influencing higher cognitive functions in various early subspecies of hominins. Next generation sequencing of Homo heidelbergensis and Homo erectus genomes and complete reconstruction of DNA sequence of the orthologous subtelomeric chromosomes in Great Apes should enable more precise timing of HSA2 formation and better understanding of its evolutionary consequences.

No MeSH data available.


Related in: MedlinePlus

A suggested gorilla-like [46] polygamous pedigree of a putative early modern human clan in which HSA2 was transmitted, implemented, and its heterozygous status converted to homozygous. A male carrier of a de novo heterozygous HSA2 (half filled square, IInd generation), had multiple children (IIIrd generation) with a few female partners. Analogous to carriers of Robertsonian translocations, he is expected to have had healthy progeny with balanced 48 (blank square/circle) and 47 (half filled square/circle) chromosomes in addition to multiple miscarriages due to chromosomal imbalances (filled triangles). Note that the unions between individuals with 47 chromosomes heterozygous for HSA2 likely produced healthy children with balanced 48 and 47 chromosomes as well as heathy subjects with 46 chromosomes (homozygous for HSA2, IVth generation). The latter individuals are expected to have had an unaffected fecundity when inbreeding with carriers of balanced 46 chromosomes homozygous for HSA2. The evolutionary advantage might have resulted from an enhanced fertility e.g. due to testis-expressed DDX11L2. Alternatively, assortative mating between individuals with higher cognitive functions due to genomic loss (heterozygous or homozygous) of gene(s) important for brain development or function might have facilitated the successful spreading of HSA2
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Fig2: A suggested gorilla-like [46] polygamous pedigree of a putative early modern human clan in which HSA2 was transmitted, implemented, and its heterozygous status converted to homozygous. A male carrier of a de novo heterozygous HSA2 (half filled square, IInd generation), had multiple children (IIIrd generation) with a few female partners. Analogous to carriers of Robertsonian translocations, he is expected to have had healthy progeny with balanced 48 (blank square/circle) and 47 (half filled square/circle) chromosomes in addition to multiple miscarriages due to chromosomal imbalances (filled triangles). Note that the unions between individuals with 47 chromosomes heterozygous for HSA2 likely produced healthy children with balanced 48 and 47 chromosomes as well as heathy subjects with 46 chromosomes (homozygous for HSA2, IVth generation). The latter individuals are expected to have had an unaffected fecundity when inbreeding with carriers of balanced 46 chromosomes homozygous for HSA2. The evolutionary advantage might have resulted from an enhanced fertility e.g. due to testis-expressed DDX11L2. Alternatively, assortative mating between individuals with higher cognitive functions due to genomic loss (heterozygous or homozygous) of gene(s) important for brain development or function might have facilitated the successful spreading of HSA2

Mentions: (1) Given the high structural complexity of the genomic region flanking the HSA2 fusion site on chromosome 2q13 and the fact that no HSA2 junction polymorphisms have been identified in modern humans, it is very unlikely that HSA2 fusion was a recurrent genomic rearrangement. I propose that HSA2 arose only once likely in one early modern human male and was subsequently transmitted and accumulated as a heterozygous event, converted to the homozygous state due to inbreeding in a small “bottleneck” polygamous clan (Fig. 2), and spread in the succeeding populations.Fig. 2


One pedigree we all may have come from – did Adam and Eve have the chromosome 2 fusion?
A suggested gorilla-like [46] polygamous pedigree of a putative early modern human clan in which HSA2 was transmitted, implemented, and its heterozygous status converted to homozygous. A male carrier of a de novo heterozygous HSA2 (half filled square, IInd generation), had multiple children (IIIrd generation) with a few female partners. Analogous to carriers of Robertsonian translocations, he is expected to have had healthy progeny with balanced 48 (blank square/circle) and 47 (half filled square/circle) chromosomes in addition to multiple miscarriages due to chromosomal imbalances (filled triangles). Note that the unions between individuals with 47 chromosomes heterozygous for HSA2 likely produced healthy children with balanced 48 and 47 chromosomes as well as heathy subjects with 46 chromosomes (homozygous for HSA2, IVth generation). The latter individuals are expected to have had an unaffected fecundity when inbreeding with carriers of balanced 46 chromosomes homozygous for HSA2. The evolutionary advantage might have resulted from an enhanced fertility e.g. due to testis-expressed DDX11L2. Alternatively, assortative mating between individuals with higher cognitive functions due to genomic loss (heterozygous or homozygous) of gene(s) important for brain development or function might have facilitated the successful spreading of HSA2
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC5037601&req=5

Fig2: A suggested gorilla-like [46] polygamous pedigree of a putative early modern human clan in which HSA2 was transmitted, implemented, and its heterozygous status converted to homozygous. A male carrier of a de novo heterozygous HSA2 (half filled square, IInd generation), had multiple children (IIIrd generation) with a few female partners. Analogous to carriers of Robertsonian translocations, he is expected to have had healthy progeny with balanced 48 (blank square/circle) and 47 (half filled square/circle) chromosomes in addition to multiple miscarriages due to chromosomal imbalances (filled triangles). Note that the unions between individuals with 47 chromosomes heterozygous for HSA2 likely produced healthy children with balanced 48 and 47 chromosomes as well as heathy subjects with 46 chromosomes (homozygous for HSA2, IVth generation). The latter individuals are expected to have had an unaffected fecundity when inbreeding with carriers of balanced 46 chromosomes homozygous for HSA2. The evolutionary advantage might have resulted from an enhanced fertility e.g. due to testis-expressed DDX11L2. Alternatively, assortative mating between individuals with higher cognitive functions due to genomic loss (heterozygous or homozygous) of gene(s) important for brain development or function might have facilitated the successful spreading of HSA2
Mentions: (1) Given the high structural complexity of the genomic region flanking the HSA2 fusion site on chromosome 2q13 and the fact that no HSA2 junction polymorphisms have been identified in modern humans, it is very unlikely that HSA2 fusion was a recurrent genomic rearrangement. I propose that HSA2 arose only once likely in one early modern human male and was subsequently transmitted and accumulated as a heterozygous event, converted to the homozygous state due to inbreeding in a small “bottleneck” polygamous clan (Fig. 2), and spread in the succeeding populations.Fig. 2

View Article: PubMed Central - PubMed

ABSTRACT

Background: In contrast to Great Apes, who have 48 chromosomes, modern humans and likely Neandertals and Denisovans have and had, respectively, 46 chromosomes. The reduction in chromosome number was caused by the head-to-head fusion of two ancestral chromosomes to form human chromosome 2 (HSA2) and may have contributed to the reproductive barrier with Great Apes.

Results: Next generation sequencing and molecular clock analyses estimated that this fusion arose prior to our last common ancestor with Neandertal and Denisovan hominins ~ 0.74 - 4.5 million years ago.

Hypotheses: I propose that, unlike recurrent Robertsonian translocations in humans, the HSA2 fusion was a single nonrecurrent event that spread through a small polygamous clan population bottleneck. Its heterozygous to homozygous conversion, fixation, and accumulation in the succeeding populations was likely facilitated by an evolutionary advantage through the genomic loss rather than deregulation of expression of the gene(s) flanking the HSA2 fusion site at 2q13.

Conclusions: The origin of HSA2 might have been a critical evolutionary event influencing higher cognitive functions in various early subspecies of hominins. Next generation sequencing of Homo heidelbergensis and Homo erectus genomes and complete reconstruction of DNA sequence of the orthologous subtelomeric chromosomes in Great Apes should enable more precise timing of HSA2 formation and better understanding of its evolutionary consequences.

No MeSH data available.


Related in: MedlinePlus