Yeast cells of mating type a are genetically engineered to produce only mating factor α instead of the normal mating factor a. The gene for the mating factor receptor was unaltered. How will these engineered cells behave in terms of mating?

Explanation:

These engineered cells will mate with each other or with normal mating type a cells, but not with normal mating type α  

The sexual cell types of yeast are designated a and α, which are correspondingly conferred by the MATa and MATα alleles of the mating type locus (MAT)

Cells of opposite type can mate to establish a cell of the MATα/MATa diploid state because both MAT alleles are co-dominant, such diploid cells are sterile but can undergo meiosis and sporulation to form asci, each of which contains two MATa and two MATα haploid spores

the answer to your question is b