The phrase "an ancestral pair" is correct and usable in written English.
It can be used when referring to two individuals or entities that are considered to be the original or early ancestors of a particular lineage or group.
Example: "The study focused on the genetic traits passed down from an ancestral pair that lived thousands of years ago."
Alternatives: "a founding couple" or "a progenitor duo".
In mice and rats, an inbred strain is defined as a population that was established with a single ancestral pair and has been inbred (brother × sister) for 20 or more consecutive generations (Guidelines for Nomenclature of Mouse and Rat Strains).
Cytogenetic and DNA marker analyses suggested that Group 1 and Group 2 have homomorphic and heteromorphic sex chromosome pairs (XY), respectively, and that the sex chromosome pairs of the two groups evolved from a common ancestral pair.
In particular, loss of different members of an ancestral duplicate pair in different species can lead to a gene tree that does not reflect the species tree [11] [13].
Heterokaryotypy may result from differential gene loss or gain as the sex chromosome complement evolves from an ancestral homologous pair.
Dosage compensation was probably acquired gradually in the course of sex chromosome evolution, as sex chromosomes are thought to arise by divergence of an ancestral autosome pair [ 6].
Halving the apparent dosage of X-linked genes in female mammals via XCI presents an evolutionary conundrum: if sex chromosomes evolve from an ancestral autosomal pair, it is the heterogametic sex that would be impelled to compensate for the complete loss or degradation of the evolving Y.
While in both XY and ZW systems the sex chromosomes arose from an ancestral autosome pair and genes became lost on the Y and W chromosomes due to the absence of recombination with a homolog, the two different systems might have required different dosage compensation solutions.
For example, for a C/T SNP with ancestral allele C, the ancestral pair of nucleotides is C G and the derived pair of nucleotides is T A.
Although most of the paleoduplicated blocks evolved following the subgenome dominance rules derived from targeted gene deletion and transposition on the sensitive subgenomes, one ancestral pair of duplicated chromosomes evolved in an exceptional manner.
