THE RELATION OF OXYGEN POSTTREATMENT AND HETEROCHROMATIN TO X-RAY-INDUCED CHROMOSOME ABERRATION FREQUENCIES IN CREPIS CAPILLARIS

Journal Article · Thu Jan 01 04:00:00 EST 1959 · Genetics (U.S.)

OSTI ID:4248452

Sire, M W; Nilan, R A

Resting seeds of Crepis capillaris were x irradiated at 1500 or 3500r and then stored under 100 lbs oxygen pressure for periods up to 42 days. The frequencies of abnormal cells, dicentric chromosomes, and acentric rod and isodiametric fragments increased during the post -irradiation oxygen treatment. Non-irradiated seeds exhibited an appreciable frequency of chromosome aberrations after 42 days of the oxygen treatment. Oxygen had no influence on the proportion of breaks in each chromosome because it uniformly increased the aberrations in all six chromosome arms. However, oxygen did appear to inhibit the restitution and rejoining processes since the ratio of breaks that did rejoin to those that did not rejoin decreased during the postirradiation treatment. In both x- irradiated and stored x-irradiated seeds, certain arms exhibited frequencies of breaks leading to dicentric chromosomes and simple breaks (those that do not rejoin or restitute) that significantly differed from the frequencies expected on the basis of length of arms. The cause of this apparent non randomness was found in the relation of euchromatin and heterochromatin to chromosome breaks. Breaks leading to dicentrics occurred in or near the heterochromatic areas whereas the simple breaks occurred in the euchromatic areas of the chromosome arms. When the observed frequencies of breaks were compared with the lengths of heterochromatin and euchromatin in each arm, they equalled the expected freguencies. It is concluded that x-ray induced breakage probably occurs at random in Crepis capillaris chromosomes, and the apparent non randomness of these breaks is due to the differential influence of euchromatin and heterochromatin on the rejoining process. The frequency of intrahomologous exchanges observed equalled the expected frequency. However, higher than expected frequencies of chromatid breaks were found; most of these breaks occurred in the long arm of D. (auth)

• Research Organization: State Coll. of Washington, Pullman
• NSA Number: NSA-13-015009
• OSTI ID: 4248452
• Journal Information: Genetics (U.S.), Journal Name: Genetics (U.S.) Vol. Vol: 44; ISSN GENTA
• Country of Publication: Country unknown/Code not available
• Language: English

Related Subjects

BIOLOGY AND MEDICINE
CHROMOSOMES
CYTOLOGY
GENETICS
MUTATIONS
OXYGEN
PLANTS
PRESSURE
QUANTITY RATIO
RADIATION DOSES
RADIATION EFFECTS
RADIATION INJURIES
SEEDS
STORAGE
VARIATIONS
X RADIATION