True-bred

The issue of a wife is unlawful seed; And none's legitimate, but mongrel breed. Thou, and thy branches, have quite cross'd the strain, We ne'er shall see a true-bred whelp again.

Source: wiktionary

The Henny strain never breeds a long-tailed cock unless crossed. The contrary has been stated by many persons, but the mistake has arisen from various birds which have not been true-bred Henny, but only the product of some cross; such will, of course, breed both kinds of plumage, but the true-bred Henny never does.

Source: wiktionary

Notwithstanding, there is no reason why a toy English bulldog should not be accomplished; but, equally, there is no reason why the true-bred French bulldog should not be preserved in its integrity, and recognised as such by the Kennel Club.

Source: wiktionary

Well, for two of them, I know them to be as true-bred cowards as ever turn'd back; and for the third, if he fight longer than he sees reason, I 'll forswear arms.

Source: wiktionary