Highly differentiated heteromorphic sex chromosomes were found in the karyotypes of Pyxicephalus adspersus (= Rana adspersa) and analysed with the various banding methods. The W chromosome is considerably smaller than the Z chromosome and consists to a great proportion of constitutive heterochromatin. The chromosome lengths and the DNA content of this species have the lowest values determined in the Ranidae to date. The nucleolus organizer regions in the chromosomes reveal a high frequency of inter-individual variations (duplications, triplications) and aberrations. In one female animal, a translocation between the W chromosome and a nucleolus organizer was identified. Preliminary results indicate, that the same chromosome pair which in P. adspersus constitutes the heteromorphic sex chromosomes is still in an initial stage of morphological differentiation in P. delalandii. Although the ZZ/ZW sex chromosomes in Pyxicephalus have developed independently of the ZZ/ZW sex chromosomes in birds and reptiles, they seemed to have passed through identical stages of morphological differentiation. In this process, the heterochromatinization of the W chromosome had a decisive function.

Chromosome banding in Amphibia

A new theory of attraction and liking based on kin selection suggests that people detect genetic similarity in others in order to give preferential treatment to those who are most similar to themselves. There are many sources of empirical and theoretical support for this view, including (1) the inclusive fitness theory of altruism, (2) kin recognition studies of animals raised apart, (3) assortative mating studies, (4) favoritism in families, (5) selective similarity among friends, and (6) ethnocentrism. Specific tests of the theory show that (1) sexually interacting couples who produce a child are genetically more similar to each other in blood antigens than they are either to sexually interacting couples who fail to produce a child or to randomly paired couples from the same sample; (2) similarity between marriage partners is most marked in the more genetically influenced of sets of anthropometric, cognitive, and personality characteristics; (3) after the death of a child, parental grief intensity is correlated with the child's similarity to the parent; (4) long-term male friendship pairs are more similar to each other in blood antigens than they are to random dyads from the same sample; and (5) similarity among best friends is most marked in the more genetically influenced of sets of attitudinal, personality, and anthropometric characteristics. The mechanisms underlying these findings may constitute a biological substrate of ethnocentrism, enabling group selection to occur.

Genetic similarity, human altruism, and group selection

I Evolution of Vertebrate Sex Chromosomes and Genomes- 1 Evidence Indicating that the X and the Y or the Z and the W were Originally an Homologous Pair of Ordinary Chromosomes- 2 Differentiation of the Primitive Sex Elements at the Expense of the Y or W, and the Conservation of the Original X or Z- 3 Polyphyletic Evolution of Vertebrates- 4 Conservation of the Original X and Homology of the X-linked Genes in Placental Mammals- 5 Conservation of the Original Z-Chromosome by Diverse Avian Species and Homology of the Z-linked Genes- II Evolution of Dosage Compensation Mechanism for Sex-linked Genes- 6 The Basic Difference in Constitution between the Mammalian X and the Drosophila X- 7 The Two Different Means of Achieving Dosage Compensation for X-linked Genes Employed by Drosophila and Mammals- 8 Various Consequences of the Dosage Compensation by X-inactivation- 9 The Conservation of the Original X and Dosage Compensation in the Face of X-polysomy- 10 Three Different Consequences of X-autosome Translocation- 11 The Consequences of Y-autosome Translocation and the XO as the Normal Female of Certain Mammalian Species- 12 Apparent Absence of Dosage Compensation for Z-linked Genes of Avian Species- III On So-called Sex Determining Factors and the Act of Sex Determination- 13 Elucidation of So-called Sex-determining Factors- 14 Time and Place of Action of Sex-determining Factors in Ontogeny- Author Index

Sex Chromosomes and Sex-Linked Genes

Chromosome banding in Amphibia: I. Constitutive heterochromatin and nucleolus organizer regions in Bufo and Hyla

Nuclear DNA mass in cells from a reference species can be used to obtain high-resolution estimates of DNA mass from a target species. In our study of DNA mass in cells from 45 selected species, representing each of the major vertebrate classes, we have obtained values of from 1.5 to 110.0 pg of DNA. Because values in or near this range would be expected in the study of nuclear DNA mass in vertebrates and other organisms, the species in this report can provide a useful catalogue of references for comparative studies of DNA.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/cyto.990100606

Reference standards for flow cytometry and application in comparative studies of nuclear DNA content

Nuclear DNA amounts of fifteen species of placental mammals were determined by Feulgen cytophotometry. Relative values for several widely used species have been ascertained with an error of only a few percent. Absolute values (picograms or numbers of nucleotide pairs) can be determined with an error of about ten percent. The largest known mammalian genome contains about twice the DNA of the smallest one. The modal diploid DNA amount for mammals is slightly above eight picograms.

Genome size in mammals.

Nuclear DNA amounts of twenty-three species of birds from seventeen families of seven orders were determined by Feulgen cytophotometry. Genome size is constant in these birds, the ratio between the largest and smallest genome in the sample is 1.3 to 1. The modal diploid DNA amount for birds is about 3.6 picograms, slightly higher than previously reported. The data point towards an evolutionary control of genome size regardless of chromosome number. Birds represent an example of a group in which reduction of genome size is correlated with active speciation.

Genome size in birds

Nuclear DNA amounts have been determined for 42 species of crustaceans bringing the total number of species with known nuclear DNA content to over 70. Genome size in Crustacea varies over a 25-fold range with a modal value of 2 to 3 pg haploid being common in many groups. Both average genome size and the amount of variability among species are characteristic for certain groups. A trend towards small genomes is evident in advanced and specialized crustacean groups. Somatic polyploidy is a very pronounced feature of the Crustacea. The data suggest that evolution by polyploidy may be more common in crustaceans than earlier data had indicated. These features and the presence of very characteristic satellite fractions in the nuclear DNA recommend the Crustacea for further studies in evolutionary genetics.

Nuclear DNA amounts in pacific Crustacea.

Specific nuclear DNA amounts were determined by Feulgen and gallocyanin chromalum cytophotometry in nine species of Bufo. These were compared with published data on DNA amounts and chromosome numbers. Together, estimates of the absolute DNA amounts of twelve species of Bufo are presented. Highest and lowest DNA amounts found in species with 22 chromosomes relate as 1.6∶1; one species with 20 chromosomes shows the lowest DNA amount determined to date.

Specific nuclear DNA amounts in toads of the genus Bufo.

Measurements of the initial slope of the Feulgen hydrolysis curve allow the precise determination of specific nuclear DNA amounts. The low stain densities involved preclude density-dependent systematic error. Best estimates of the nuclear DNA amount for sixteen salamander species are presented.

Konrad Bachmann

Papers

Genome size in mammals.

Genome size in birds

Nuclear DNA amounts in pacific Crustacea.

Specific nuclear DNA amounts in toads of the genus Bufo.

Feulgen slope determinations of urodele nuclear DNA amounts