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2.
A comparative description of mitochondrial DNA differentiation in selected avian and other vertebrate genera 总被引:14,自引:1,他引:13
Levels of mitochondrial DNA (mtDNA) sequence divergence between species
within each of several avian (Anas, Aythya, Dendroica, Melospiza, and
Zonotrichia) and nonavian (Lepomis and Hyla) vertebrate genera were
compared. An analysis of digestion profiles generated by 13-18 restriction
endonucleases indicates little overlap in magnitude of mtDNA divergence for
the avian versus nonavian taxa examined. In 55 interspecific comparisons
among the avian congeners, the fraction of identical fragment lengths (F)
ranged from 0.26 to 0.96 (F = 0.46), and, given certain assumptions, these
translate into estimates of nucleotide sequence divergence (p) ranging from
0.007 to 0.088; in 46 comparisons among the fish and amphibian congeners, F
values ranged from 0.00 to 0.36 (F = 0.09), yielding estimates of P greater
than 0.070. The small mtDNA distances among avian congeners are associated
with protein-electrophoretic distances (D values) less than approximately
0.2, while the mtDNA distances among assayed fish and amphibian congeners
are associated with D values usually greater than 0.4. Since the
conservative pattern of protein differentiation previously reported for
many avian versus nonavian taxa now appears to be paralleled by a
conservative pattern of mtDNA divergence, it seems increasingly likely that
many avian species have shared more recent common ancestors than have their
nonavian taxonomic counterparts. However, estimates of avian divergence
times derived from mtDNA- and protein-calibrated clocks cannot readily be
reconciled with some published dates based on limited fossil remains. If
the earlier paleontological interpretations are valid, then protein and
mtDNA evolution must be somewhat decelerated in birds. The empirical and
conceptual issues raised by these findings are highly analogous to those in
the long-standing debate about rates of molecular evolution and times of
separation of ancestral hominids from African apes.
相似文献
3.
Methods for computing the standard errors of branching points in an evolutionary tree and their application to molecular data from humans and apes 总被引:23,自引:2,他引:21
Statistical methods for computing the standard errors of the branching
points of an evolutionary tree are developed. These methods are for the
unweighted pair-group method-determined (UPGMA) trees reconstructed from
molecular data such as amino acid sequences, nucleotide sequences,
restriction-sites data, and electrophoretic distances. They were applied to
data for the human, chimpanzee, gorilla, orangutan, and gibbon species.
Among the four different sets of data used, DNA sequences for an
895-nucleotide segment of mitochondrial DNA (Brown et al. 1982) gave the
most reliable tree, whereas electrophoretic data (Bruce and Ayala 1979)
gave the least reliable one. The DNA sequence data suggested that the
chimpanzee is the closest and that the gorilla is the next closest to the
human species. The orangutan and gibbon are more distantly related to man
than is the gorilla. This topology of the tree is in agreement with that
for the tree obtained from chromosomal studies and DNA-hybridization
experiments. However, the difference between the branching point for the
human and the chimpanzee species and that for the gorilla species and the
human-chimpanzee group is not statistically significant. In addition to
this analysis, various factors that affect the accuracy of an estimated
tree are discussed.
相似文献
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Iodination and biosynthesis of rat thyroglobulin 总被引:4,自引:0,他引:4
7.
Anonymous nuclear DNA markers in the American oyster and their implications for the heterozygote deficiency phenomenon in marine bivalves 总被引:4,自引:0,他引:4
A puzzling population-genetic phenomenon widely reported in allozyme
surveys of marine bivalves is the occurrence of heterozygote deficits
relative to Hardy-Weinberg expectations. Possible explanations for this
pattern are categorized with respect to whether the effects should be
confined to protein-level assays or are genomically pervasive and expected
to be registered in both protein- and DNA-level assays. Anonymous nuclear
DNA markers from the American oyster were employed to reexamine the
phenomenon. In assays based on the polymerase chain reaction (PCR), two
DNA-level processes were encountered that can lead to artifactual genotypic
scorings: (a) differential amplification of alleles at a target locus and
(b) amplification from multiple paralogous loci. We describe symptoms of
these complications and prescribe methods that should generally help to
ameliorate them. When artifactual scorings at two anonymous DNA loci in the
American oyster were corrected, Hardy-Weinberg deviations registered in
preliminary population assays decreased to nonsignificant values.
Implications of these findings for the heterozygote-deficit phenomenon in
marine bivalves, and for the general development and use of PCR-based
assays, are discussed.
相似文献
8.
Comparative tumor morphogenesis of two human colon adenocarcinoma cell clones xenografted in the immunosuppressed newborn rat 总被引:1,自引:0,他引:1
Lionel Rémy Marie-France Jacquier Noucha Daémi Jean-François Doré Jean-Claude Lissitzky 《Differentiation; research in biological diversity》1993,54(3):191-200
Abstract. Involucrin is a precursor of the keratinocyte cornified envelope that is specifically expressed in the suprabasal layers of the epidermis and other stratifying squamous epithelia. To study involucrin gene expression and the function of involucrin, we expressed a 6 kb DNA fragment of the human involucrin gene, containing approximately 2.5 kb of upstream sequence and 0.5 kb of downstream sequence, in transgenic mice. The transgene produces a 68 kDa protein that is detected by a human involucrin-specific antibody, and is expressed in a tissuespecific and differentiation-appropriate manner (i.e., expression is confined to the suprabasal layers of the epidermis, extocervix, trachea, esophagus and conjunctiva).
Soluble involucrin levels are two to four times higher in transgenic epidermal keratinocytes compared to human foreskin keratinocytes. Newborn heterozygous animals have a normal birth weight and a normal appearing epidermis and hair growth begins at 4 to 5 days of age (i.e., the same time as hair growth in non-transgenic animals). In a subpopulation of the newborn homozygous animals birth weight is reduced, the epidermis is scaly and hair growth begins late, at around 9 to 10 days of age. In addition, the hair tends to stand erect on both heterozygous and homozygous adult animals giving the appearance of diffuse alopecia.
Immunofluorescent and electron microscopy localize involucrin in the hair follicle and cornified envelope, respectively. These results suggest that overexpression of involucrin may cause abnormalities in hair follicle structure/function and cornified envelope structure. These animals provide a new model for the study of cornified envelope structure and function. 相似文献
Soluble involucrin levels are two to four times higher in transgenic epidermal keratinocytes compared to human foreskin keratinocytes. Newborn heterozygous animals have a normal birth weight and a normal appearing epidermis and hair growth begins at 4 to 5 days of age (i.e., the same time as hair growth in non-transgenic animals). In a subpopulation of the newborn homozygous animals birth weight is reduced, the epidermis is scaly and hair growth begins late, at around 9 to 10 days of age. In addition, the hair tends to stand erect on both heterozygous and homozygous adult animals giving the appearance of diffuse alopecia.
Immunofluorescent and electron microscopy localize involucrin in the hair follicle and cornified envelope, respectively. These results suggest that overexpression of involucrin may cause abnormalities in hair follicle structure/function and cornified envelope structure. These animals provide a new model for the study of cornified envelope structure and function. 相似文献
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