Coenospecies — 31 — Conditional Dominance 



of the average performance of the lines involved" (Sprague 

 & Tatum). 



Commiscuum. — A group consisting of all the organisms which 

 are capable of being intercrossed. 



Communal Connubium. — A group of individuals within 

 which mating is promiscuous. 



Comparate Chiasmata. — Symmetrical chiasmata, i.e. chias- 

 mata which are either reciprocal or complementary, q.v. 0pp. 

 Disparate Chiasmata. 



Comparium. — A commiscuum, q.v. 



Compatible. — Readily capable of fertilization. 



Complement. — A collective term for the group of chromo- 

 somes in a single nucleus whether somatic or gametic. 



Complementary Chiasmata. — Chiasmata formed between 

 four chromatids in such a way that the first chiasma occurs 

 between two of the chromatids and the second between their 

 homologues. 



Complementary Factor. — A factor which only in conjunc- 

 tion with one or more other genes, controls a particular char- 

 acter. 



Complete Penetrance. — Said of a dominant gene whose 

 presence in an organism always produces an effect on that 

 organism, or of a recessive gene whose presence in the homozy- 

 gous state always produces an effect. See also Penetrance and 

 Incomplete Penetrance. 



Complete Sex Linkage. — This occurs when the gene con- 

 cerned is located on that portion of the X-choromosome which 

 has no homologous segment in the Y-chromosome. A few cases 

 are known of complete sex linkage where the gene concerned 

 is carried on the short terminal portion of the Y-choromosome 

 which has no homologous segment in the X-chromosome. 



Compound Determiners. — Two or more genes which to- 

 gether make a particular character phenotypically evident. 



Compound X-chromosomes. — A group of chromosomes 

 which, in certain forms, acts in place of the usual X-chromo- 

 some. This group acts as a compound X during spermato- 

 genesis (e.g. Ascaris incurva which has 8X + lY). 



Conception. — Fertilization in animals, particularly in humans. 



Condensation or Contraction, of the chromosome. The thick- 

 ening shortening and spiralization of the chromatids during 

 prophase (Darlington). 



Conditional Dominance. — Used of a gene which produces 

 an effect in the heterozygous state but the homozygote of 

 which is, as yet, unknown. 



