A species of cereal rye (Secale cereale) has a chromosome number of 14, while a species of Canadian wild rye (Elymus canadensis) has a chromosome number of 28. Sterile hybrids can be produced by crossing Secale with Elymus. Given that none of the chromosomes pair at meiosis I in the sterile hybrid (Hang and Franckowlak, 1984), speculate on the anaphase I separation patterns of these chromosomes.

Key Concepts

Chromosome Number and Meiosis

Chromosome number refers to the total number of chromosomes in a cell. In meiosis, homologous chromosomes pair up and segregate into daughter cells. In the case of the sterile hybrid between Secale cereale (14 chromosomes) and Elymus canadensis (28 chromosomes), the mismatch in chromosome numbers leads to difficulties in pairing during meiosis, resulting in no homologous chromosomes aligning at meiosis I.

Hybrid Sterility

Hybrid sterility occurs when the offspring of two different species are unable to reproduce. In this case, the hybrid between Secale and Elymus is sterile because the differing chromosome numbers prevent proper pairing and segregation during meiosis, leading to gametes that lack the necessary genetic material for successful reproduction.

Anaphase I and Chromosome Separation

Anaphase I is the stage of meiosis where homologous chromosomes are pulled apart to opposite poles of the cell. In the sterile hybrid, since no chromosomes pair during meiosis I, the separation pattern would involve random movement of unpaired chromosomes, leading to an unequal distribution and potentially resulting in gametes with varying and incomplete sets of chromosomes.