Glossary I 331 



Thymine the pyrimidine (2,4-dihydroxy-S-methylpyrimidine) involved 

 in the structure of DNA but not RNA. 



Transduction a mechanism of gene transfer in bacteria in which genetic 

 material is transferred from one cell to another by bacteriophage. 



Transformation a change in the genetic information of a bacterium as 

 a result of exposure to a DNA extract of a bacterium of different ge- 

 netic constitution. 



Transhydrogenation the sequential transfer of electrons in cellular oxi- 

 dation cycles. 



Translocation see reciprocal translocation. 



Trans state two mutational alterations in cistrons on different homol- 

 ogous chromosomes; see cis state. 



Trisomic describing an organism with one chromosome in the comple- 

 ment represented three times. 



Univalent a chromosome lacking a homologue and therefore unsynapsed 

 at the first meiotic prophase. 



Uracil the pyrimidine (2,4-dihydroxypyrimidine) involved in the struc- 

 ture of RNA but not DNA. 



Variance a measure of dispersion obtained by squaring the deviations 

 of the individuals from the mean and dividing the result by the num- 

 ber of individuals; the square of the standard deviation. 



Viability the capability for living or continuing to develop; often incor- 

 rectly used as synonymous with fitness. 



Vivipary in plants, vegetative reproduction in which propagules replace 

 flowers in the inflorescence; in animals, the production of living young 

 rather than eggs. 



Wild type the most frequently observed phenotype, or the phenotype 

 arbitrarily designated as "normal." 



