Segregation of chromosomes in sperm of reciprocal translocation carriers: a review

Reciprocal translocations, the most frequent structural aberration in humans, are mainly transmitted by one of the parents. In order to analyze the chromosomal content of the spermatozoa from carriers of chromosomal reorganizations, two methods have been used, karyotyping of sperm chromosomes by the human-hamster system and fluorescence in situ hybridization (FISH) in decondensed sperm nuclei. In this work, we review 92 sperm chromosome segregation studies from 85 different reciprocal translocation carriers, including a triple translocation carrier. Using the human-hamster method, a total of 5,818 spermatozoa from 44 reciprocal translocation carriers have been analyzed, 43 of them carrying a single reciprocal translocation and one was a carrier of a double reciprocal translocation. A segregation analysis in a carrier of a t(2;22;11) has been also reported. Carrying out FISH in sperm nuclei, a total of 237,042 spermatozoa from 46 reciprocal translocation carriers have been analyzed. Six of these were also analyzed by the human-hamster system. Taking into account both methods, a total of 76 different reciprocal translocations have been studied. In 74 of these 76 translocations, the reorganization occurs between autosomes, and in the other two, the Y chromosome is involved. Although along general lines, there are similarities between the results obtained by the two methods of analysis, variations are observed when the distribution of the different types of segregations that produce imbalances is compared. As a general rule reciprocal translocation carriers produce more unbalanced sperm than normal or balanced sperm. The results reported also corroborate that the proportion of unbalanced forms depends on the characteristics of the reorganization and that it varies widely. Thus the importance of performing a detailed meiotic behavior analysis for each particular translocation in order to obtain enough information to give adequate genetic counseling is stressed. Aspects as to the possible overestimation of 3:1 segregations or the presence of interchromosomal effects still need to be elucidated.     

Testicular chromosomes of Gallus domesticus

Summary Testes of Gallus domesticus were studied (a) by light microscopy after hypotonic treatment followed by acetic-alcohol fixation and airdrying and (b) by electron microscopy of osmium-fixed, araldite-embedded material, some of which was pretreated with hypotonic solutions.The following conclusions were reached: (i) The number of chromosome pairs at meiosis is constant and is most probably 40 (although 39 or 38 is possible). (ii) The diploid chromosome number at mitotic metaphase cannot be certainly determined by light microscopy but there is no reason to suppose it is not double the number of meiotic bivalents. (iii) No essential difference in structure was found between long and short bivalents at meiosis by light or electron microscopy; the lengths of the bivalents at pachytene form a continuous series, (iv) Some short bivalents appear to contain less material per unit length than long ones; this could explain why these chromosomes cannot always be resolved by light microscopy when fully contracted. (v) So-called macro- and micro-chromosomes differ only in size, but not in behaviour, at mitosis and meiosis.     

Specific arrangement of chromosomes in the spermiogenesis of Gallus domesticus

On the chromosomes of the rooster the constitutive heterochromatin (C-bands) is to be found for the most part at the centromeres. The position of the centric heterochromatin in spermatids and sperm is not randomly distributed. In early, round spermatids one heterochromatic block lies at this exact position on the membrane that develops into the tip of the sperm nucleus (acrosomal chromocenter). During the elongation of the spermatid nucleus another heterochromatic block comes to lie on the basal nuclear membrane. The other centromeres arrange themselves tandem-wise between the acrosomal and the basal chromocenters. Comparisons have been made between this specific arrangement and the location of chromosomes in the sperm of amphibians and mammalians.     

Segregation of chromosomes in sperm of Robertsonian translocation carriers

Robertsonian translocations are the most frequent structural chromosomal abnormalities in humans and can affect fertility, with various degrees of sperm alterations in men; or the pregnancy outcome of the carriers. The studies on meiotic segregation of chromosomes in sperm of Robertsonian translocation males find a majority of normal or balanced spermatozoa for the chromosomes related to the translocation (mean 85.42%; range 60-96.60%). Furthermore, recent studies suggest an interchromosomal effect. Studies on spermatozoa from translocation carriers, and in mouse models help the comprehension of the meiotic segregation mechanisms. Results of meiotic segregation analysis in man could be integrated in genetic counselling especially when assisted reproductive technology is required.     

Chronology and pattern of replication in the bone marrow chromosomes of Gallus domesticus

The duration of the cell generation, the chronology, and the pattern of chromosome duplication was studied in the bone marrow of Gallus domesticus. The duration of the phases of the cell cycle is: cell generation 17.5 hours, S period 9 hours. G₂ period plus prophase stage 2.5 hours, G₁ period 6 hours. Chromosome replication begins at many sites. During middle S it extends to the whole complement and finally finishes in small, late replicating regions of the macrochromosomes. Interchromosomal asynchrony of duplication at the initiation or at the end of the S period was not observed. Z-chromosomes begin and finish DNA synthesis synchronously with the other macrochromosomes. The W-chromosome in females is the last microchromosome to finish replication. However it ends DNA synthesis at about the same time as the macrochromosomes. Similarities and differences between chromosome replication in Aves and Mammalia are considered.     

Precise location of breakpoints in a frequent reciprocal translocation between chromosomes 11 and 22

One of the most frequent chromosomal translocations in human beings is 11q/22q, which results in the "partial trisomy of 22q syndrome." However, the breakpoint on the long arms of chromosomes 11 and 22 is still a matter of controversy. In the present study, we have used chromosomes from lymphocytes of a neonate who happened to have this classical abnormality, and by R-banding prometaphase chromosomes with acridine orange it has been possible to establish that the translocation between chromosomes 11 and 22 resulted from 3:1 meiotic maternal nondisjunction. A detailed analysis of the chromosome regions involved in this translocation revealed that the breakpoints on chromosomes 11 and 22 were at 11q23.3 and 22q11.1, respectively.     

Body weight, semen quality, and age at sperm production of hemicastrated and intact cockerels (Gallus domesticus)

Spermatozoa were found earlier in the ejaculates of hemicastrated cockerels and the mean body weight of the hemicastrates was significantly (P less than 0.01) greater than that of the intact cockerels. The mean values for sperm concentration/ml, and total spermatozoa in the ejaculates of the hemicastrates were significantly greater (P less than 0.01) than those of the intact cockerels. Differences existed between the hemicastrates bearing the left testis, and those bearing the right testis in respect of age at sperm production, sperm/concentration and total spermatozoa in the ejaculate.     

Crossing over in chicken (Gallus gallus domesticus) oogenesis: Periodic arrangement of chiasmata over chromosomes

The periodic occurrence of chiasmata was studied in lampbrush chromosomes of the chicken (Gallus gallus domesticus). It was shown that the most probable interference distance in chicken macrobivalents 1–3 corresponded to 24.48 Mb. The distance at which absolute interference is observed in chicken macrochromosomes varies from 5.75 to 9.02 Mb.     

Identification of two lipid binding proteins from liver of Gallus domesticus

1. Two low molecular weight (approximately 14,000 Da) proteins exhibiting lipid binding activity were purified from liver cytosol and identified as non-specific lipid binding protein (ns-LTP) and fatty acid binding protein (L-FABP). 2. Ligand binding assays indicated that ns-LTP exhibited greater binding activity for cholesterol and little binding of fatty acids. Conversely, L-FABP had higher relative binding activity for fatty acids but did not bind cholesterol. 3. Amino acid composition and pI data supported the identification of the chicken liver lipid binding proteins as L-FABP and ns-LTP. 4. Polyclonal antisera was prepared against each of the liver lipid binding proteins and monospecificity verified using Western blot analysis.     

Soluble fetoproteins in chorioallantoic membrane from chick embryo (Gallus domesticus).

1. Anti-chorioallantoic membrane (CAM) serum was made fetal-specific by absorbing it in a mixture of egg white, fresh yolk and chicken serum, plus liver, lung, heart and spleen from a laying hen. 2. By immunoelectrophoresis, the CAM extract shows three soluble transitory proteins, an oncofetal protein (alpha-fetoprotein) and a soluble organ permanent protein from some of the organs used in the absorption. 3. By assaying crossed heterologous systems, alpha fetoprotein was found in the allantoic, amniotic and yolk fluids after 14 days of incubation; all three proteins were found in amniotic, but neither in allantoic nor in yolk fluid.