1. Cytological analysis of chromosome association at metaphase I was made in the parents and the hybrids of Sorghum vulgare x S. halepense, S. vulgare x S. almum, S. almum x S. halepense, S vulgare x S. arundinaceum, and S. vulgare x S. verticilliflorum. S. halepense and S. almum have 2n = 40, and the others have 2n = 20. 2. Heterosis was apparent in all hybrids with the exception of S. almum x S. halepense, which showed very little hybrid vigor. The chromosome number was determined for eleven of the seventeen hybrids of S. vulgare x S. halepense; one hybrid had 2n = 30, and ten had 2n = 40. Association of chromosomes at metaphase I was studied in three of these hybrids, and it was concluded from the type of pairing in the hybrids and the parents that one genome in S. halepense is similar to the genome in S. vulgare. Data also indicate that S. halepense arose as a segmental allopolyploid with only two genomes and that its chromosomal complement now consists predominantly of one genome, which is similar to that of S. vulgare. 3. The chromosome number of twelve hybrids of S. vulgare x S. almum showed that one had 2n = 30, two had 39, and nine had 40. One hybrid of S. almum x S. halepense had 2n = 39, and two had 2n = 40. Pairing of chromosomes in the analyzed hybrids supports the assumption of other workers that S. almum is a segregate from a cross between S. vulgare and S. halepense. The data further show that most of the genetic complement of S. almum is composed of chromosome segments of S. vulgare. It is concluded that a grain sorghum type crossed with S. halepense to produce S. almum. Bridges and fragments were observed in anaphase I in the two 40 -chromosome species and in all hybrids. 4. Cytological studies of hybrids between the 20-chromosome species revealed only bivalent pairing and normal meiosis, except for an infrequent bridge and fragment at anaphase I of two of the hybrids.

Recent advances in cytology

\Botanical < ~Gazette CYTOLOGICAL STUDIES OF SOME SPECIES AND HYBRIDS IN THE EU-SORGHUMS

John Erickson is associate professor of biology at Western Washington University, Bellingham 98225. He studied at Yankton College, Omaha University, Indiana University, and was awarded a Ph.D. by University of Oregon. Dr. Erickson has published several articles on chromosome breakage and chromosome behavior at meiosis, appearing in American Naturalist, Genetics, and Canadian Journal of Genetics and Cytology. He notes, ". . . I had no intention of being a text author when I prepared the original 1979 article ... while it was in press I got involved, and am now under contract with West Publishing Company for a genetics text. When I gently took the genetics texts to task, I never dreamt, that I would be authoring one of them myself." Other interests include hiking, sailing, swimming, and enjoying his grandchildren. Biological nomenclature, Schrader wrote in 1953, has long been at its worst in dealing with the centromere, or kinetochore. Since then the situation has gotten no better. Figure 1 illustrates a major aspect of the problem. Discussion and resolution have long been in order. To start the dialogue, I published a review-inquiry article in The American Biology Teacher (Erickson 1979). The article surveyed description and illustration of the centromere by 40 texts in biology, genetics, and cytology. Copies were sent to all cited authors. Only five responded. A letter was then sent to 38 cytologists and cytogeneticists, and 16 responded. This report is based largely on the responses, and on materials the respondents sent along. Names of those responding will be found in the acknowledgments.

Defining the Centromere

Chiasma Formation in a Heteromorphic Bivalent in Belamcanda chinensis, Leman

A model of crossing-over based on alternately-oriented dipoles.

When the organising committee of the thirteenth chromosome conference asked me to prepare the opening lecture, I realised that it would be the last one this century. In fact the next one will be held at the beginning of the third millennium A.D., in 2001. While thinking along these lines it occurred to me just how important this century has been in the development of cytogenetics!

Recent advances in cytology

Citations

\Botanical < ~Gazette CYTOLOGICAL STUDIES OF SOME SPECIES AND HYBRIDS IN THE EU-SORGHUMS

Defining the Centromere

Chiasma Formation in a Heteromorphic Bivalent in Belamcanda chinensis, Leman

A model of crossing-over based on alternately-oriented dipoles.

Chromosomes yesterday: a century of chromosome studies

Related Papers (5)

Variation and Evolution in Plants

Animal cytology and evolution.

The Cell In Development And Heredity

Cytology and cytogenetics

Types of polyploids; their classification and significance.