Sequences homologous to oncogeneyes (Y73/Esh/sarcoma viral oncogene cDNA) in theDrosophila melanogaster Oregon genome were detected byin situ hybridization on salivary gland chromosomes. Three separate sites, 8D/X, 57BC/2R and 95CD/3R, were identified. Presence of sequences highly homologous toyes in the genomic DNA was confirmed by dot blot hybridization under high stringency conditions.

The proto-oncogeneyes encodes a protein tyrosine kinase described as a member of the non-receptor protein tyrosine kinases family (NRPTK). We have identified two clones from the genomic library ofDrosophila melanogaster which hybridized to thev-yes oncogene (encoded by the Y73/Esh Avian Sarcoma Virus). These clones represent two different genomic sequences fromDrosophila. By RNA slot blot hybridization, we have demonstrated the presence ofyes homologous sequences in the RNA of larvae (the third instar), pupae and an embryonic cell line ofDrosophila. On northern analysis of the cell line RNA, three transcripts (3.8, 2.0 and 1.0 kb) hybridized with theyes sequence. Oncogeneyes is thus well conserved across widely separated phylogenetic lines like human, chicken andDrosophila indicating involvement in essential biological functions.

By employing a procedure that combines ELISA and photoacoustic spectroscopy, we have examined the content of 5-methylcytosine (m⁵C) in DNA of individuals who differed from one another in the number of X chromosomes in their genomes. The results show that the human inactive X chromosome (Xi) contains very high amounts of this modified nucleotide. We estimate that in the 46, XX female there is more m⁵C in Xi (∼ 3.6 x 10⁷) than in all the remaining chromosomes put together (∼2.1 x 10⁷). Our results also suggest that nearly one-fifth of all cytosines in Xi are methylated and that, in addition to CpG methylation, there is extensive non-CpG methylation as well.

There are evidences to show that response to ionizing radiations have genetic influence. To investigate this further, reciprocal F₁ hybrids were genereted by crossbreeding the radiation-susceptible BALB/c mouse strain with resistant C57BL/6 in a sex-specific manner (BALB/c♂×C57BL/6♀ = B6BcF₁; C57BL/6♂× BALB/c♀ =BcB6F₁). These hybrids were compared with each other and to the parental strains with respect to transcriptional responses to low-dose ionizing radiation exposure (LDIR). The two F₁ hybrids showed drastic differences in their gene expression profiles to ionizing radiation exposure particularly in case of the genes involved in DNA damage response and repair process. Also, the inheritance pattern of the gene expression was found to be complex and could not be explained solely on the basis of parental expression pattern. It was concluded that there is a differential transmission of susceptible trait alleles from the parents to F₁ progeny which is dependent on the sex of the parent mouse strain used to set up the crosses and other environmental factors.