Evidence for the Evolutionary Model

Chimp/Human Alus & RH/α-globin Genes: Red Herrings & Falsehood

Creationist claim:

"Chimps have more alpha-hemoglobin genes and more Rh bloodgroup genes, and fewer Alu repeats, in their genome than humans. " --micah1116

α-globin genes:

      Humans have two α-globin genes; HBA1 and HBA2, which are both at locus 16p13.3 ("HBA1," nd; "HBA2," nd). Not only do chimps also have two α-globin genes (Liebhaber & Begley, 1983), but "human and chimpanzee G-gamma, A-gamma, alpha, and beta globin sequences are identical (Goodman, Moore, & Barnabas, 1972, p.43)."

      And if that wasn't bad enough, not only does the tight grouping of the α-globin genes indicate they came about by duplication (Orkin, 1978), but there is a great deal of evidence that duplication of globin genes has occurred many times throughout their evolutionary history (Goodman, Moore, & Barnabas, 1972). Since they are clearly prone to duplicate, differing counts would not be a problem anyway. As usual, not only is the claim false, but even if it were true, the implied claim (that it would be problematic for the evolutionary model) would still be false.

RH genes:

      Humans have two types of RH genes (RHD and RHCE). Chimps and gorillas have three types of RH genes (intron 3/intron 4—CE/CE, D/D1, CE/D2, where RHCE=CE/CE  RHD=D/D1  D2=D1+12-bp duplication). The only difference is that humans have one less intron to work with in putting to together alleles.

      And it is true that chimpanzees have 3 RH genes per haploid genome, where as humans and gorillas have two (only one in other primates), but this is easily explained by a duplication, since the different RH genes themselves arose from an ancestral RH duplication in the human-chimp-gorilla ancestor.

      So here's the timeline; an Alu-Sx inserted in the RH intron 4 of the Anthropoidea common ancestor. Then, in the human-chimp-gorilla ancestor, RH duplicated into RHD and RHCE, and the RHD intron 4 experienced a 654-bp deletion (along with the Alu-Sx) and a 12-bp duplication (GAGCAGGTTCAG) just 3' of that deletion. In the human linage, the gene with the intron 4 duplication was lost (Apoil & Blancher, 2000).

Alu repeats:

      Humans have ~1.09×10^6 Alu repeats (IHGS Consortium, 2001, Table 11, p.880). But only 7082 are not found in orthologous loci in chimpanzees (lineage-specific to humans), and chimpanzees only have 2340 lineage-specific Alu repeats (CSA Consortium, 2005, Table 2, p.75). So the difference in the number of Alu repeats is only ~0.4%.


 

But as small as the difference is, the cause for it is understood:

      The majority of human Alu repeats are of the new, largely human-specific subfamilies Ya5, Yb8, Ya8, and Yb9, where as the majority in chimpanzees are of Yc1 (Hedges et al., 2004; Batzer & Deininger, 2002). Yc1 is similar to the ancestral source gene, where as the aforementioned newer Alus are divergent from the ancestral source gene (CSA Consortium, 2005, p.74).

       So between a decline in Alu activity in chimpanzees, the new Alu subfamily source genes in humans, and the small time those new Alus have had to replicate, it is clear as to why humans have a fraction of a percent more Alu repeats than chimpanzees.

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References:

Apoil, P. A., and A. Blancher. "Rh Gene Evolution in Primates: Study of Intron Sequences." Mol Biol Evol 17.1 (2000 Jan): 127-36. <http://mbe.oxfordjournals.org/cgi/content/full/17/1/127>.

Goodman, M., G. W. Moore, J. Barnabas, and G. Matsuda. "The Phylogeny of Human Globin Genes Investigated by the Maximum Parsimony Method." J Mol Evol 3.1 (1974 Feb 28): 1-48. <http://www.springerlink.com/content/p5120442pkw117u8/>.

"HBA1 Hemoglobin, Alpha 1 [Homo Sapiens]." Entrez Gene. National Center for Biotechnology Information. Web. 18 Mar. 2010. <http://www.ncbi.nlm.nih.gov/gene/3039>.

"HBA2 Hemoglobin, Alpha 2 [Homo Sapiens]." Entrez Gene. National Center for Biotechnology Information. Web. 18 Mar. 2010. <http://www.ncbi.nlm.nih.gov/gene/3040>.

Liebhaber, S. A., and K. A. Begley. "Structural and Evolutionary Analysis of the Two Chimpanzee Alpha-globin MRNAs." Nucleic Acids Res 11.24 (1983 Dec 20): 8915-29. <http://www.ncbi.nlm.nih.gov/pmc/articles/PMC326634/?tool=pmcentrez>.

 

Orkin, S. H. "The Duplicated Human Alpha Globin Genes Lie Close Together in Cellular DNA." Proc Natl Acad Sci U S A 75.12 (1978 Dec): 5950-4 <http://www.ncbi.nlm.nih.gov/pmc/articles/PMC393094/?tool=pubmed>.

Batzer, M. A., and P. L. Deininger. "Alu Repeats and Human Genomic Diversity." Nat Rev Genet 3.5 (2002 May): 370-9. <http://www.ncbi.nlm.nih.gov/pubmed/11988762>.

Chimpanzee Sequencing and Analysis Consortium. "Initial Sequence of the Chimpanzee Genome and Comparison with the Human Genome." Nature 437.7055 (2005 Sep 1): 69-87. <http://www.nature.com/nature/journal/v437/n7055/full/nature04072.html>.

Hedges, D. J., P. A. Callinan, R. Cordaux, J. Xing, E. Barnes, and M. A. Batzer. "Differential Alu Mobilization and Polymorphism among the Human and Chimpanzee Lineages." Genome Res 14.6 (2004 Jun): 1068-75. <http://genome.cshlp.org/content/14/6/1068.long>.

International Human Genome Sequencing Consortium. "Initial Sequencing and Analysis of the Human Genome." Nature. 409.6822 (2001 Feb 15): 860-921. <http://www.nature.com/nature/journal/v409/n6822/full/409860a0.html>