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Frequency of Orientation of Normal and Interchanged Chromosomes in Barley Interchange Heterozygotes 1
Author(s) -
Ramage R. T.,
Humphrey D. F.
Publication year - 1964
Publication title -
crop science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.76
H-Index - 147
eISSN - 1435-0653
pISSN - 0011-183X
DOI - 10.2135/cropsci1964.0011183x000400050032x
Subject(s) - geneticist , library science , citation , biology , genetics , computer science
TRISOMICS occur in the progeny of interchange heterozygotes as a result of 3:1 disjunction of the configuration of four chromosomes at anaphase I. In barley (Hordeum vulgare L.) such 3:1 disjunction usually occurs when two of the chromosomes are oriented and two are noncooriented in the metaphase I spindle (1). The normal chromosomes may be oriented and the interchanged chromosomes noncooriented, or the interchanged chromosomes may be oriented and the normal chromosomes noncooriented (Figure 1). The type of orientation of the configuration of four chromosomes will determine the type of trisomic individuals obtained from the interchange heterozygote. In (n+1) gametes, the extra chromosome will be an oriented chromosome and the haploid complement will contain the noncooriented chromosomes. Gametes resulting from 3:1 disjuncttion of a configuration with the normal chromosomes oriented will have the two interchanged chromosomes plus an extra normal chromosome. Gametes resulting from 3:1 disjunction of a configuration with the interchanged chromosomes oriented will have normal chromosomes plus an extra interchanged chromosome. Such gametes will result in p r i m a r y and tertiary t r i somic types, repectively (2). The frequencies of the two types of orientation may be determined by cytological examinatiton of trisomics found in the progeny of interchange heterozygotes in which the interchanged chromosomes are recognizable. For translocations in which the interchanged chromosomes are not recognizable, a method has been devised which will give an estimate of the frequencies of the two types of orientation. This method requires an interchange heterozygote that is also heterozygous for a marker gene located on the centromere segment and closely linked with the break-point of the interchange, and set up so that the normal chromosome carries the recessive and the interchanged chromosome carries the dominant allele of the marker gene. The interchange Tl—6a and the gene pair O o (green vs. orange lemma), which is located on chromosome 6 (3), were