A Karyological Study of Tenualosa Ilisha (Hamilton, 1822) From the Confluence of Padma and Meghna River of Bangladesh

Tenualosa ilisha (Hamilton, 1822), commonly known as Hilsha shad is a valuable and highly acceptable species in terms of their high flavored properties. Hilsha shad has striking morpho-genetical adaptation to heterogeneous habitats across their migratory routes. Cytogenetic analysis demonstrates the changes in chromosomes. But none was focused on the cytogenetic analysis of T. ilisha in Bangladesh. T. ilisha was found to possess 2n = 42 number of chromosomes along with a karyotype formula: 1M + 31m + 8sm + 2st using giemsa staining technique. The results demonstrated ‘diffuse type of interphase nuclei, co-existence of continuous type and interstitial type of prophase chromosomes respectively. No heteromorphic sex chromosomes were determined cytologically. The presence of diverse types of chromosomes based on centromeric position, gradual decrease in total haploid chromosome complement, mean centromeric asymmetry, coefficient of variation of chromosome length and Stebbins’s classification highlighted its asymmetry in karyotype with advance nature. Therefore, the elemental karyological data will offer information for the proper identification, cytotaxonomical classification, expanding productivity and preservation of genetic resources ofT. ilisha. Bangladesh J. Zool. 49 (2): 243-255, 2021

B-Chromosomes in Gymnosperms

B-chromosomes show a non-random distribution in different taxa of gymnosperms. They are generally smaller and show similar centromeric position as the normal complement and are heterochromatic in nature and may show DAPI or CMA banding. They are generally devoid of any gene content, do not pair at meiosis and show accumulation through female line. They show incremental effect on genome size and some adaptive value in particular ecological conditions.

A Karyological Study in Some Species of Coffea L. and in the Closest Relative Psilanthus travancorensis (Wight & Arn.) J.-F. Leroy

Chromosome characterization were carried out in Coffea kapakata A. Chev (Bridson), C. racemosa Lour., C. salvatrix Swynn. & Philipson and in Psilanthus travancorensis (Wight & Arn.) J.-F. Leroy (2n=22) by employing the conventional acetic orcein technique as well as by C- and NOR-banding aiming further comparative studies. Although C. canephora and C. dewevrei have already been studied and depict a C-band karyotype, they have also been included for further comparisons, since NOR-banding and some other morphometric data have not been obtained yet. However, there were observed some differences among the species regarding chromosomal morphometry. The karyotype formula obtained was 3m+6sm+2sms for C. salvatrix and P. travancorensis, 1M +2m + 6sm + 2sms for C. kapakata and 2M +1m + 6sm + 2sms for C. racemosa. All species displayed a moderate karyotype asymmetry and according to Stebbins system, C. canephora, C. dewevrei, C. kapakata and C. racemosa were classified as 3B while C. salvatrix and P. travancorensis were classified as 2A. Among the four indices used to assess karyotype asymmetry, Paszko AI index along with Stebbins were best suited to individualize the species. C-bands were preferentially situated at a pericentromeric/centromeric position. Two pairs of chromosomes, with secondary constriction and satellite segments, were observed in all the species following acetic orcein staining. C. racemosa and C. salvatrix showed NOR-band in both pairs, while only one chromosome pair carrying NOR-band was seen in C. canephora, C. dewevrei, C. kapakata and P. travancorensis. Data on chromosome morphometry, asymmetry indices and NOR-banding were suitable for the characterization of the species.

Karyotype and RAPD Analysis in Five Potato Varieties (Solanum tuberosum L.)

Two native and three high yielding potato varieties available in Bangladesh were studied cytogenetically at molecular level to get a preliminary idea about their genomes. These varieties possess 2n = 4x = 48 chromosomes. Each variety has definite centromeric formula. Presence of maximum metacentric chromosomes suggested their karyotypes as symmetric type. The range of individual chromosomal and total length of 2n chromosome complements was also distinct in five varieties. Heteromorphicity regarding centromeric position suggesting the occurrence of structural aberration in respective homologous pairs. Seven primer combinations were used for RAPD finger printing. A few common RAPD bands suggested the sharing of genomic fragments among five varieties. However, each variety showed specific characteristic RAPD bands. Therefore, each variety has characteristic karyotype and RAPD markers. DOI: http://dx.doi.org/10.3329/bjb.v41i1.11088 Bangladesh J. Bot. 41(1): 105-110, 2012 (June)

C-banded karyotypes of Brassica campestris, B. oleracea, and B. napus

The chromosome complements of three Brassica species, namely B. campestris (2n = 20), B. oleracea (2n = 18), and B. napus (2n = 38), were studied using the air-dry method and C-banding. Karyotypes and ideograms of late prophase chromosomes were constructed, since contracted metaphase chromosomes were generally not suitable for this purpose. The three species generally had a similar banding pattern, manifested in the presence of a centromeric C-band in all chromosomes and heterochromatic knobs at the telomeric end of some chromosomes. The centromeric C-bands were more pronounced in B. campestris than in B. oleracea. Depending on the centromeric position, the chromosomes were grouped into median, submedian, subterminal, and terminal types. All chromosome pairs were morphologically distinguishable. Only one nucleolar chromosome pair, with heterochromatic satellites, was observed in each species. When compared, it was possible to distinguish chromosomes of both B. campestris and B. oleracea type in B. napus, but conclusive evidence as to the origin of all chromosome pairs in B. napus was not at hand.Key words: Brassica, chromosomes, late prophase, C-bands, knob structures, karyotypes, idiograms.

Visualization of kinetochores in mammalian meiotic preparations and observations of argentophilic differences between mitotic and meiotic kinetochores

Brief staining with AgNO3 was found to differentially stain the kinetochores of chromosomes from diakinesis – metaphase I and metaphase II nuclei of mammals. The results differ from those of Giemsa-stained or C-banded preparations as the silver-stained meiotic kinetochores are clearly distinguishable from both constitutive heterochromatin and euchromatin. Silver-staining is presented as a valuable method for the staining of meiotic material because it allows for the positive identification of centromeric position and orientation with respect to chiasmata. The nonargentophilic nature of the centromere (kinetochore) region of spermatogonial metaphase chromosomes in some species suggests a fundamental structural difference between mitotic and meiotic kinetochores.Key words: kinetochore, meiosis, mammal.

COMPUTER-ORIENTED ANALYSIS OF HUMAN CHROMOSOMES IV. DEOXYRIBONUCLEIC ACID-BASED CENTROMERIC INDEX

A density-oriented semiautomatic method to estimate centromeric index is described and tested on 4611 human chromosomal images. Chromosomes are stained for deoxyribonucleic acid with gallocyanin-chrome alum and their optical density is recorded by a digital scanning microscope. Shape information in the chromosome boundary leads to a provisional centromeric position. The chromosome is divided into strips 0.25-0.35 µm wide paralleling the centromere. Optical density is integrated within each strip, strips are assembled into a density profile and the definitive centromere is located at the major local minimum in the profile. Centromeric index (large arm:total) is based on optical density or area. A test set of 4611 chromosomal images is based on over 2500 chromosomes (56 metaphase cells from six individuals) and excludes overlapped and excessively bent chromosomes. The program fails in 1.2% of the test images. Standard deviation within chromosome groups of centromeric index based on density is 0.024 and replication error is 0.016. Systematic differences between area-based and density-based measurements are observed and interpreted.