 However, homozygotes for recessive lethal mutations are , per definition , non-viable, which necessitates maintenance of the mutation in heterozygous organisms . Crosses between heterozygotes yield a wild-type organisms , in addition to hetereozygotes and the non-viable homozygotes.
<meaning-changed>  However, homozygotes for recessive lethal mutations are , per definition , non-viable, which necessitates maintenance of the mutation in heterozygous organisms . Crosses between heterozygotes yield a wild-type organisms , in addition to hetereozygotes and the non-viable homozygotes.
 However, homozygotes for recessive lethal mutations are , per definition , non-viable, which necessitates maintenance of the mutation in heterozygous organisms instead (in which a chromosome containing a recessive lethal/sterile mutation is complemented by a homolog that functions as wild-type at the same locus, allowing the organism to survive and reproduce more or less normally). Crosses between heterozygotes yield a wild-type organisms , in addition to hetereozygotes and the non-viable homozygotes.