DNA synthesis in duplicate-type sex chromosomes of the Indian house shrew, <i>Suncus murinus</i> (Insectivora)

Abstract

Replication patterns of the duplicate-type sex chromosomes have been studied in bone-marrow cells in vivo and fetal cells in vitro of the Indian house shrew, Suncus murinus. The sex chromosomes start their replication along with the rest of the chromosomes in the early S but show asynchrony in the late S phase. The Y chromosome finishes its DNA synthesis earlier than the X chromosome and the autosomes in male bone-marrow and fetal cells. On the other hand, the X chromosomes in female cells behave differently in bone-marrow and fetal cells. One of the X’s replicates early in fetal cells. But there is no definite pattern in bone-marrow cells – the X chromosomes can replicate either early or late. The duplicate-type X chromosome of Suncus is unique among mammals in its replication; the pattern does not conform to the hypothesis that except 5% of the haploid complement residing in the X chromosome is functional. The correlation between genetic activity and late or early replication is discussed. It is proposed that heteropycnosis is merely a reflection of out-of-phase replication and not necessarily genetic inertness.

Cytogenetical studies on insectivora. II. Geographical variation of chromosomes in the house shrew, Suncus murinus (soricidae), in east, southeast and southwest asia, with a note on the karyotype evolution and distribution.

“…We found house shrews with 40 chromosomes at some other localities, Bogor (Java), Makassar (Celebes), Tainan (Taiwan), and Kanpur and Bhubaneswar (India). The same chromosome number has been reported from Malacca (Yong 1974) and Johore Bahru (Sam et al 1979) in southern Malaysia, Delhi in northern India (Rao et al 1970), Hyderabad and Karwar located in central India (Satya Parakash and Aswathanarayanan 1976) and Con Son Island of South Vietnam (Duncan et al 1970) . No variation was found in the autosomes and the X chromosome in all of these animals, but the Y chromosome showed local variations.…”

“…The median-sized submetacentric Y chromosome has also been found in central India (Satya Parakash and Aswathanarayanan 1976). On the other hand, a large submetacentric Y chromosome, similar to the Kanpur specimens, was found in Delhi (Rao et al 1970) . The animals collected in South Vietnam, however, had a small acrocentric Y (Duncan et al 1970) .…”

“…The chromosome number of this species has been first reported by Tateishi (1938) who found that the diploid number was 40 in the Formosan specimens. This chromosome number was subsequently confirmed by Manna and Talukdar (1967), Ray-Ohaudhuri et al (1968) and Rao et al (1970) for the Indian taxon, Yosida et al (1968) for the Japanese taxon, and Duncan et al (1970) for the South Vietnamese taxon. On the other hand, variable chromosome numbers from 2n=40 to 36, by Robertsonian translocation, have been found by Yong (1971Yong ( , 1972 in the West Malayan population.…”

“…1) Cited from Rao et al (1970), 2) from Satya Parakash and Aswathanarayanan (1976), 3) from Yong (1974), 4) from Ando et al (1980), 5) from Yong (1971Yong ( , 1972, 6) from Obara and Miyai (1981), 7) from Manna and Talukdar (1967), 8) from Duncan et al (1970).…”

Geographic Variation in the Sex Chromosomes of the West Malaysian House ShrewSuncus Murinus(Insectivora, Soricidae)

“…The chromosomes of this insectivore have been extensively studied in different parts of Asia (DuNCAN, VAN PEENEN and RYAN 1970;MANNA and TALUKDAR 1967;RAo, SHARMA and SHAH 1970;RAY-CHAUDHURI, RANJINI and SHARMA 1968;SHARMA, PATHAK and RAY-CHAUDHURI 1970;SHARMA, RAo and SHAH 1969;TATEISHI 1938;YoNG 1971YoNG , 1972YosmA, MoRIGU-CHI and SoNODA 1968 ). Only Robertsonian-type autosomal polymorphism has been reported in the West Malaysian ( = Malayan) taxon (YoNG 1971(YoNG , 1972.…”