IV.6. Report from Genetic Stock Center at Fort Collins, Colorado.
T. Tsuchiya, Dept. of Agronomy, Colorado State University, Fort Collins, Colorado 80521, U.S.A.
1. Genetic Stock for ac3.
The albino mutant for ac3 was obtained in the barley variety Colsess and the stock for this mutant was named as Colsess II (Robertson, 1929, Genetics 14:1-36; Robertson and Austin, 1935, J. Agr. Res. 51:435-440). In 1970 and 1971 when the genetic stocks were distributed, a wrong stock was sent to some workers by mistake; the stock sent was not ac3 but a3 which was originally obtained by Nilson-Ehle (1922, Hereditas 3:191-199) and studied by Hallquist (1926, Hereditas 8:229-254).
Persons who received the stock for "ac3" please check the material received from Stock Center in Colorado (T. Tsuchiya). The differences between stocks for ac3 and a3 are shown in the following table:
If you still have the seeds used in your experiments, please send some of them back to me. I will check their characteristics.
2. The Genetic Stock for zbc??
The gene symbol zbc for zebra striped leaves (Colorado) appeared first in Supplement III of the summary series by Robertson et al. (1965) as the recommended symbol for zc used by Woodward (1957). This gene has also been used by other workers (Albrechtsen, 1957; Doney, 1961; Kasha and Walker, 1960). The linkage data obtained for zbc and other markers are as follows:
Another similar mutant zoned leaf was given a recommended symbol z (Robertson et al. 1947) for the previous symbol zd used by Immer and Henderson (1943) who found the linkage between K and z (zd) with cross over value of 6.0 + 0.8.
No data on the allelism testing between these two markers are available.
The stock for zbc has been distributed rather widely throughout the world. Recent critical study of the gene zbc by means of trisomic analysis caused some doubt as to the chromosomal location of this gene.
The stock for zbc was crossed with the primary trisomic for chromosome 4 (Robust) and F2 segregation was studied with the following results:
No chromosome count was made in the first and third experiments. In the second experiment the chromosome numbers of all recessive homozygotes were counted with the following results: Five out of 20 recessive homozygotes were trisomic plants. The X2 value for 3:1 ratio fit to disomic expectation and an appreciable number of recessive homozygotes were trisomic plants.
According to Burnham (1962, Table 85, p. 190), the percentage of recessive homozygotes in the trisomic portion should not be more than 2.8% or the ratio of A:a should be 35:1 in the trisomic section. The transmission of trisomics in Robust is about 35% in selfed progeny (F2) of trisomic F1 hybrids. Therefore, the number of trisomics in this F2 population (a total 85 plants) is calculated as about 30. Five recessive plants were trisomics which amount to 25% of trisomic portion. This percentage of trisomic recessive homozygotes is too high for this gene, zbc, to be in trisomic ratio in this cross. Therefore, it is concluded that zbc is not located on chromosome 4. Critical analysis is necessary by means of trisomic analysis using six other trisomic stocks to designate the specific chromosome on which this gene is located.
There is a question whether this stock (CSU, B8-9) is really zbc. The stock could be something else. Allelism testing between this "zbc" and zc used by Dr. Woodward and his students is now underway. The stock for zc has also been used in crosses with the primary trisomic for chromosome 4 to test its chromosomal location.
References:
1. Albrechtsen, R. S. 1957. M.S. Thesis, Utah State Univ.
2. Burnham, C. R. 1962. Discussions in cytogenetics.
3. Doney, D. L. 1961. M.S. Thesis, Utah State Univ.
4. Immer, F. R. and M.T. Henderson. 1943. Genetics 28:419-440.
5. Kasha, K. J. and G. W. R. Walker. 1960. Can. J. Genet. Cytol. 2: 397-415.
6. Robertson, D. W., G. A. Wiebe and R. G. Shands. 1947. J. Am. Soc. Agr. 39:464-473.
7. Robertson, D. W., G. A. Wiebe, R. G. Shands and A. Hagberg. 1965. Crop Sci. 5:33-43.
8. Woodward, R. W. 1957. Agron. J. 49:28-32.
