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Biomedical subjects

H M Chapman

Publications and source records attributed to H M Chapman.

33 records · Page 2Linked to original sources
PubMed1977

Chromosome morphology during meiosis of normal and Robertsonian translocation-carrying rams (Ovis aries).

A detailed description is given of the meiotic chromosomes of the normal ram (54,XY) and of the chromosomes at diakinesis-metaphase I in rams heterozygous for the t1, t2 and t3 and homozygous for the t1 and t3 Robertsonian translocation chromosomes. Analyses were made on diakinesis-metaphase I chromosomes in 309 cells from normal rams and 2402 cells from the Robertsonian translocation carriers. Hypomodal cell counts were due to missing chromosomal elements and hypermodal counts were due either to separation of the chromosomes of the sex bivalent or to separation of the components of an autosomal bivalent. Trivalent formation was characteristic for the heterozygous Robertsonian translocation carriers while the homozygous carriers had an additional large bivalent. An association between the sex bivalent and a small autosomal bivalent at diakinesis-metaphase I is reported.

Animals↗
PubMed1975

The frequency of aneuploidy in the secondary spermatocytes of normal and Robertsonian translocation-carrying rams.

A detailed analysis was made of the chromosomes in 1008 M II figures from three different types of heterozygous Robertsonian translocation-carrying rams (53,xy,t1; 53,xy,t3) and 225 M II figures from homozygous Robertsonian translocation-carrying rams (52,xy,t1t1; 52,xy,t3t3) and rams of normal karotype (54,xy). No hypermodal cells were recorded in either the normal or the homozygous rams, but from 4-5% to 9-2% of M II cells from the heterozygous rams were hypermodal. The heterozygous rams also produced a significantly higher level of hypomodal cells suggesting that, in addition to non-disjunction, lagging at anaphase I may have occurred. There were also distinct differences in M II aneuploid spermatocyte frequency between heterozygous versus normal and homozygous rams. Fewer balanced translocation X-carrying M II cells were recorded than expected in three of the four 53,xy,t2 rams. This coincides with mating data which suggest that 26,x,t2 gametes may occur less frequently than expected. Since ewes of normal karotype mated to 53,xy,t rams conceive to first service at a rate equal to or better than normal mating groups, and because no blastocysts with unbalanced karotypes associated with the t1 translocation have been recorded, it is suggested that only euploid spermatozoa are involved in fertilization. In the sheep, aneuploid spermatocytes probably degenerate before sperm maturation.

Aneuploidy↗
PubMedDate not supplied

Origin and significance of centric fusions in domestic sheep.

The karyotypes of 731 sheep of various breeds were studied and considered in association with previous chromosome studies of domestic sheep. A high incidence of the t2 trnslocation was found in two pedigree flocks of New Zealand Romney sheep. One of these flocks was established over 100 years ago and it is suggested that this translocation originated in the Romney Marsh breed of sheep in England. A naturally occurring double translocation heterozygote 52t1t2 was reported for the first time. A further flock of sheep of the Perendale breed was found with a high incidence of dicentric chromosome fusion that was identified as the t3 translocation. The apparently common occurrence of chromosome polymorphism, due to centric fusions, in domestic sheep is discussed in relation to karyotype evolution among both domestic and wild sheep.

Animals↗