• A. Skovsted

      Articles written in Journal of Genetics

    • Cytological studies in cotton - II. Two interspecific hybrids between Asiatic and new world cottons

      A. Skovsted

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      1. Of two interspecific hybrids between Asiatic and New World cottons studied, one had 2n = 39 and the other 2n = 52. For the latter, the inference is that a diploid egg from Asiatic cotton had functioned.

      2. In a study of the somatic chromosomes of New World cotton it has been found that half of the chromosomes are small and the other half larger, the latter being comparable in size to the chromosomes of Asiatic cotton. The small chromosomes of New World cotton are of the same size as those in diploid wild species from North America. Species from the Old World and from Australia are all characterised by the larger size of their chromosomes.

      3. In the first meiotic division it was seen that (1) at least 13 univalent chromosomes are present in both hybrids, and (2) the hybrid with 52 chromosomes shows the same chromosome conjugation as in a triploid Asiatic cotton, but with the addition of an extra set of 13 non-homologous chromosomes.

      4. The conclusion was drawn that New World cottons are allopolyploid species. It is thought that these probably originated from a cross between two species ofGossypium both withn = 13 but possessing morphologically dissimilar and non-homologous sets of chromosomes. The inference is that one of the parental species was an Asiatic cotton or a very closely allied type, while the other was probably a New World species characterised by its smaller chromosomes.

    • Cytological studies in cotton - III. A hybrid betweenGossypium Davidsonii Kell. andG. Sturtii F. Muell

      A. Skovsted

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      1.Gossypium Davidsonii (n = 13), a wild species from California, has smaller chromosomes thanG. Sturtii (n = 13), a wild species from Australia. This difference in chromosome size is maintained in the hybrid, and enables a distinction between the paternal and the maternal chromosomes to be made.

      2. The chromosome pairing in the hybrid is incomplete, but allosyndesis takes place about nine times more often than autosyndesis. Univalents are just as frequent between the small chromosomes fromG. Davidsonii, as between the larger chromosomes fromG. Sturtii.

      3. The chiasma frequency is the same in the pure species despite the difference in chromosome size. Contrasted with the pure species, the chiasma frequency in the hybrid is significantly smaller in the bivalents containing aDavidsonii and aSturtii chromosome.

      4. The difference in the size of the chromosomes of the species under observation is in all probability neither the result of genetic factors, nor associated with a difference in pairing blocks.

    • Chromosome numbers in the Malvaceae. I

      A. Skovsted

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      1. In the present study the chromosome numbers of about 120 species representing 25 genera of the family Malvaceae have been described. The following chromosome numbers were found: 5, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 21, 22, 25, 26, 28, 33, 35, 36, 38, 39, 42, 46, 56 and 65.

      2. Evidence has been presented in favour of the following chromosome series: (a) a five series (5, 10, 15, 25); (b) a six series (12, 18, 36); (c) a seven series (7, 14, 21, 28, 35, 42, 56); (d) an eleven series (11, 22, 33); and (e) a thirteen series (13, 26, 39, 65).

      3. In most genera, all species examined are members of the same chromosome series (i.e. Althaea, Pavonia, Gossypium). Some genera, however, contain different chromosome series,i.e. Abutilon (8 and 7 series);Malvastrum (12 and 15 series, and a few numbers represented by a single specimen); andHibiscus (11, 12 (18, 36), 14 (28), 17, 19 and several others). The cytological groups in these genera appear to be associated with taxonomical groups or certain morphological characters (cf. Discussion and General Summary).

    • Cytological studies in cotton - IV. Chromosome conjugation in interspecific hybrids

      A. Skovsted

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