[Human embryos and tissue cultures: scientific, ethical and legal reflections]. / Embriones humanos y cultivos de tejidos: reflexiones científicas, éticas y jurídicas.

Human cell therapy based on tissue transplantation can become an important tool in Medicine. In the last years, experimental evidence has proved that it could be possible to produce human tissue cultures derived from embryonic stem (ES) cells which are pluripotents. The topic is discussed from the scientific, ethical and legal points of view.

[Genetic reading of the decision of the Constitutional Court on the appeal on unconstitutionality against Law 35/1988 on Assisted Reproduction Techniques]. / Una lectura genética de la sentencia del Tribunal Constitucional sobre el recurso de inconstitucionalidad contra la Ley 35/1988 sobre Técnicas de Reproducción Asistida.

In this article we provide a "genetic reading" of the challenge on grounds of alleged inconstitutionality made against Spain's Law on Assisted Reproduction Techniques (Law 38/1988) and of the ruling handed down by the Constitutional Court on 17 June 1999. A critical appraisal is given of some genetic and biological concepts which, in the author's view, are used incorrectly in the legal texts presented. The article also shows that at the heart of the matter lies still the latent problem of the status in law of embryos. Lastly, brief reference is made to the issue of freedom of research.

A quantitative study of chiasma terminalization in the grasshopper Chorthippus jucundus.

The possible existence of chiasma terminalization in the grasshopper Chorthippus jucundus was tested in four males by means of comparisons between chiasma locations at diplotene and metaphase I within L3, M4 and M5 bivalents. Diplotene cells were stained by a C-banding technique to recognize heterochromatic regions, especially the centromeric ones, whereas metaphase I cells were stained by a silver staining technique that visualizes a core-like structure that extends through each homologous chromosome. The core is very pronounced at kinetochores and forms cross-shaped configurations at chiasmata. No evidence of chiasma terminalization has been found.

Nucleolus organizer competition in Triticum aestivum - Aegilops umbellulata chromosome addition lines.

The nucleolar organizer activity of wheat (Triticum aestivum, AABBDD) and Aegilops umbellulata (UU) chromosomes have been analyzed in the complete set of the chromosome addition lines by using a highly reproducible silver-staining procedure. Chromosomes 1U and 5U produce the partial inactivation of wheat nucleolar organizer chromosomes 6B, 1B and 5D. The chromosomes D and G from Ae. umbellulata, which are not SAT-chromosomes, seem to specifically influence the activity of wheat NORs. The predominant status of the U genome with respect to nucleolar competition in the Triticeae is confirmed.

On the ordered arrangement of the haploid complement in radial metaphases of secondary meiocytes of male grasshoppers, Euchorthippus pulvinatus gallicus.

Five hundred and ninety-three radial metaphase II cells from the male grasshopper, Euchorthippus pulvinatus gallicus, were analyzed to ascertain whether chromosomes in the haploid complement were in a fixed order. As an a posteriori hypothesis, the most probable original order of chromosomes in the metaphases was determined. The genetical significance of a suprachromosomal organization is discussed.

Pollen germination and tube growth in rye (Secade cereale L.) homozygous and heterozygous for reciprocal translocations.

To contribute to the knowledge of the role of reciprocal translocations in rye, a component of fertility was estimated by comparing germination and pollen tube growth in homozygous and heterozygous plants for reciprocal translocations. The results obtained indicate that there are no differences in germination and pollen tube growth rate when homozygous and heterozygous plants as a whole are compared. However, there are significant differences in pollen tube growth between plants carrying different translocations. This suggests that the chromosome constitution of a plant is relevant to these fitness-estimating parameters together with its particular genetic background.

Evidence for wheat-rye nucleolar competition (amphiplasty) in triticale by silver-staining procedure.

Amphiplasty in hexaploid triticale, the artificial amphiploid of tetraploid wheat and diploid rye, is analyzed for the first time using a modified, highly reproducible, silver-staining procedure. A comparative analysis of metaphase somatic cells by phase contrast, C-banding and silver-staining of the hexaploid triticale cv. 'Cachirulo' and its parents, namely, the tetraploid durum wheat cv. 'Enano de Andujar' and the diploid rye cv. 'Petkus' has been made. Two silver-stained nucleolar organizer regions (Ag-NORs) (the chromosome pair 1 R) are observed in all rye plants analyzed, whereas four Ag-NORs (chromosome pairs 1 B and 6 B) are found both in the tetraploid wheat parent and in the triticale. The rye Ag-NORs are absent in the triticale. Since the Agstaining reaction of NORs can be considered as an indication for genetic activity, the silver procedure can be used to visualize gene functionality at the rDNA sites with conventional light microscopy and, consequently, the modified Ag-staining method described can be very useful in analyzing the amphiplasty phenomenon in natural or artificial hybrid combinations and derivatives in the Triticum group and its relatives.

Analysis of nucleolar activity in Agropyron elongatum, its amphiploid with Triticum aestivum and the chromosome addition lines.

The nucleolar organizer activity of the Agropyron elongatum, its amphiploid with hexaploid wheat (Triticum aestivum) and the chromosome addition lines is analyzed by the silver-staining procedure. Four Ag-NORs are observed in A. elongatum corresponding to the chromosomes 6E and 7E. In the amphiploid T. aestivum - A. elongatum, eight Ag-NORs are observed which corresponds the wheat chromosomes 1B and 6B and to the elongatum chromosomes 6E and 7E. Thus, there is codominance in the nucleolar organizer activity of the chromosomes of the two species. However, a partial amphiplasty is detected since less than 8 Ag-NORs (7 up to 4) are observed in some metaphase cells; the chromosomes 6E and 7E are occasionally suppressed by wheat chromosomes. This conclusion is confirmed by the behaviour of the addition lines since only in those corresponding to the chromosomes 6E and 7E are the elongatum chromosomes nucleolar active although occasionally they can be suppressed by wheat chromosomes.

Cytogenetic structure of common wheat cultivars from or introduced into Spain.

Chromosome arrangements of twenty-eight cultivars of common wheat, Triticum aestivum L., from or introduced into Spain are compared with that of 'Chinese Spring' taken as a pattern. All the cultivars analyzed differ from 'Chinese Spring' by one or two reciprocal translocations. When 12 out of 28 cultivars were compared it was concluded that a minimum number of thirteen interchanges are present, involving at least ten different chromosomes of the complement. The interest of a reappraisal of the rôle of interchanges in the evolution of Gramineae is pointed out.

C-banding pattern and meiotic pairing in five rye chromosomes of hexaploid triticale.

The meiotic behaviour of rye chromosomes 1R, 2R, 3R, 6R and 7R/4R of hexaploid triticale 'Cachirulo' is analyzed using the C-banding technique. These chromosomes show different C-banding patterns and present different pairing levels at metaphase I. A decreasing effect of large telomeric heterochromatin bands on pairing is deduced from the following two main facts: i) The chromosome 7R/4R shows the highest pairing associated with the smallest amount of heterochromatin, ii) pairing levels of 2 R short arm and 3 R long arm which carry large telomeric bands are less than their respective long and short arms lacking telomeric heterochromatin. Possible desynaptic effects of heterochromatin are discussed although an asynaptic effect cannot be rejected.

Mutation-selection equilibrium as a possible cause of an interchange chromosome polymorphism in a cultivar of rye, Secale cereale L.

A persistent chromosomal polymorphism exists in a population of cultivated rye, Secale cereale (Candela et al. 1979). In order to ascertain the possible causes that maintain it, we have estimated the fitness values of structurally homozygous and heterozygous plants and the mutation rate of spontaneous interchange. The estimates of the selection coefficient against heterozygotes (s=0.15-0.40) and of the mutation rate u=6.12×10(-2) support a mutation-selection equilibrium as a likely cause of the interchange chromosome polymorphism.

Ultrastructural aspects of tetrads with micronuclei in a wheat monosomic.

Meiosis of monosomics produces tetrad cells with micronuclei. These micronuclei consist exclusively of one chromosome, the critical chromosome. The electron microscope study of these cells reveals that, in the main nucleus the chromatin is relatively uncondensed with large numbers of perichromatin structures and the nucleolus is almost exclusively fibrillar. This corresponds with a phase of active extranucleolar synthesis and moderate nucleolar activity as reported by other authors using biochemical techniques. The chromatin of the micronucleus is in a more condensed stage than in the main nucleus which, in our opinion, is due to a later beginning of interphase. A nuclear envelope surrounds the micronucleus. In its interior, a patch of nucleolar material can be seen. From the available data on the phylogenetic evolution of this special chromosome which constitutes the micronucleus, we suggest that there must be a partial expression of the nucleolar genes carried by this chromosome due to the absence of the factors which impair their expression in disomic plants.

A new approach to quantitative analysis of somatic association.

A formula is proposed for estimating statistically the degree of somatic chromosome association during metaphase. Standard chi-square tests can then be used to determine the presence or absence of somatic association between homologous chromosomes in selected species. The method requires that the chromosomes be morphologically distinguishable and that their circular arrangement on the metaphase plate has not been distorted by the squash used during their preparation.

The transmission of rye B chromosomes in natural pollination.

This paper examines the transmission of B chromosomes in natural (but controlled) pollination, in order to obtain results which can be applied to natural populations of rye. The frequencies of the female gametes in both 2n= 14+1 and 2n=14+2 rye plants have been estimated with reference to their chromatid constitution. From the results obtained on the offspring, it seems that preferential distribution takes place during female meiosis of 2n= 14+2 plants. It has been demonstrated that pollen carrying B chromosomes formed in plants of 2n=14+2 was more competitive than normal pollen. On the contrary, when it was formed from plants 2n=14+1, B chromosome elimination by pollen was total. This process may be considered as sporophytic determination. The genetic significance of the presence of B chromosomes in natural populations is discussed. It is proposed that B chromosomes may be the cytological expression of a complex evolutionary system which results in conservation of population genetic variability.