Study of blood groups of Mahars and Marathas showing presence of sickle cell trait at Nagpur.
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Abstract Changes in gene expression are a prominent feature of morphological evolution. These changes occur to hierarchical gene regulatory networks (GRNs) of transcription factor genes that regulate the expression of trait‐building differentiation genes. While changes in the expression of differentiation genes are essential to phenotypic evolution, they can be caused by mutations within cis ‐regulatory elements (CREs) that drive their expression ( cis ‐evolution) or within genes for CRE‐interacting transcription factors ( trans ‐evolution). Locating these mutations remains a challenge, especially when experiments are limited to one species that possesses the ancestral or derived phenotype. We investigated CREs that control the expression of the differentiation genes tan and yellow , the expression of which evolved during the gain, modification, and loss of dimorphic pigmentation among Sophophora fruit flies. We show these CREs to be necessary components of a pigmentation GRN, as deletion from Drosophila melanogaster (derived dimorphic phenotype) resulted in lost expression and lost male‐specific pigmentation. We evaluated the ability of orthologous CRE sequences to drive reporter gene expression in species with modified ( Drosophila auraria ), secondarily lost ( Drosophila ananassae ), and ancestrally absent ( Drosophila willistoni ) pigmentation. We show that the transgene host frequently determines CRE activity, implicating trans ‐evolution as a significant factor for this trait's diversity. We validated the gain of dimorphic Bab transcription factor expression as a trans ‐change contributing to the dimorphic trait. Our findings suggest an amenability to change for the landscape of trans ‐regulators and begs for an explanation as to why this is so common compared to the evolution of differentiation gene CREs.
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Abstract Changes in Department of Defense regulations now permit persons with sickle cell trait to serve in all service branches. However, for purposes of the regulation, sickle cell trait is defined as 41% or less S hemoglobin. Our screening experience, based on 397 individuals with sickle cell trait, with quantitative scan of cellulose acetate electrophoretic sheets, indicates that 20–40% (depending on definition of terms) of individuals with sickle cell trait would be excluded by this criterion.
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1. This study tested the relationships between the probability of pairwise species co‐occurrence and pairwise dissimilarity in their traits in infracommunities (across assemblages harboured by conspecific individual hosts within a locality), component communities (across assemblages harboured by host species within a locality), and compound communities (across assemblages in different localities) of fleas and gamasid mites parasitic on small mammals in Western Siberia. 2. A significant, albeit weak, tendency was found for flea communities harboured by conspecific host individuals, host species, and host communities to be composed of similar species. No relationship between the probability of co‐occurrence and trait dissimilarity was detected for mite communities at any hierarchical scale. 3. For fleas, this study explained the link between positive co‐occurrence and trait dissimilarity by a process resembling environmental filtering realised mainly via host traits for infracommunities and component communities and via off‐host environment for compound communities, thus suggesting that the identical shape of the relationships between co‐occurrence and trait dissimilarity at different scales was driven by different mechanisms. 4. The explanation of the lack of this relationship in mites included: (i) the paucity of the subset of mite traits used in this study and its potential inadequacy for the question at hand; and (ii) possible masking of the effect induced by one trait on co‐occurrence owing to the lack of this effect induced by another trait(s). 5. Caution is recommended regarding the compilation of a dataset involving multiple traits, its analysis, and the interpretation of the results.
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The evolution of sexual dimorphism may occur when natural and sexual selection result in different optimum trait values for males and females. Perhaps the most prominent examples of sexual dimorphism occur in sexually selected traits, for which males usually display exaggerated trait levels, while females may show reduced expression of the trait. In some species, females also exhibit secondary sexual traits that may either be a consequence of a correlated response to sexual selection on males or direct sexual selection for female secondary sexual traits. In this experiment, we simultaneously measure the intersex genetic correlations and the relative strength of sexual selection on males and females for a set of cuticular hydrocarbons in Drosophila serrata. There was significant directional sexual selection on both male and female cuticular hydrocarbons: the strength of sexual selection did not differ among the sexes but males and females preferred different cuticular hydrocarbons. In contrast with many previous studies of sexual dimorphism, intersex genetic correlations were low. The evolution of sexual dimorphism in D. serrata appears to have been achieved by sex-limited expression of traits controlled by genes on the X chromosome and is likely to be in its final stages.
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A narrow‐leaf trait found in crimson clover ( Trifolium incarnatum L.) is characterized by oblanceolate, serrate leaflets. Crosses made between narrow‐leaf and normal‐leaf plants produced normal‐leaf F 1 plants. In the F 2 population, an acceptable fit was found to a ratio of three normal plants to one narrow‐leaf plant. The normal F 2 genotypes fit a 2:1 (segregating: nonsegregating) ratio. The heterozygous F 2 plants produced normal‐leaf to narrow‐leaf plants in a ratio of 3:1. These data indicate that narrow‐leaf is controlled by a single recessive gene. The genetic symbol, nl , is proposed to designate this recessive leaf character. This characteristic would make an excellent genetic marker since it can be identified in the seedling stage.
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Hybridization can be an evolutionary creative force by forming new polyploid species, creating novel genetic variation or acting as conduits of potentially advantageous traits between hybridizing forms. Evidence for the latter is often difficult to find because alleles under positive selection can spread rapidly across a hybrid zone and sweep to fixation. In Western Panama, an avian hybrid zone between two species of manakins in the genus Manacus exists where the unidirectional introgression of bright, yellow plumage into a white population provides evidence for the importance of hybrid zones as conduits of advantageous traits. Several lines of indirect evidence suggest that sexual selection favoring yellow plumage drives this asymmetrical spread, but more direct evidence is lacking. Along the edge of the hybrid zone, both yellow- and white-collared manakins are found in the same mating arenas or leks and compete for the same females (“mixed leks”), providing us with a unique opportunity to understand the dynamics of yellow plumage introgression. We studied these mixed leks to determine whether yellow males have a mating advantage over white males and, if so, whether the mating advantage is driven by male-male interactions, female choice, or both. We found that yellow males mated more than white males, suggesting that sexual selection favoring yellow males can, indeed, explain the spread of yellow plumage. However, we found that this advantage occurred only in mixed leks where the frequency of yellow males is greater than white males. This suggests that the advantage of yellow males may depend on the presence of other yellow males, which may slow the rate of introgression in leks where yellow frequency is low such as in areas where yellow males are beginning to colonize the white population. This, along with the geographic barrier posed by major rivers in the hybrid zone, may initially limit or slow the spread of yellow plumage. Finally, we found that yellow and white males were similar in aggression and body size, and held comparable positions within leks. Because these traits or factors are often important in or dictated by aggressive male-male interactions, these comparisons indicate that male-male interaction is not the primary mechanism for the spread of yellow plumage. However, white and yellow males received similar numbers of courtship visits from females but differed in the number of matings, suggesting that females actively rejected white in favor of yellow males. Our results indicate that sexual selection by female choice has driven the unidirectional introgression of yellow plumage into the white population, providing a mechanism for how hybrid zones act as conduits of novel and advantageous traits.
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