A cell containing two complete sets of chromosomes, one from each parent.

• A. Estrus
• B. Gestation
• C. Lactation
• D. Diploid

Answer: (D)

Two complete sets of chromosomes, one from each parent, define a diploid cell. In most organisms, body cells are diploid, containing homologous chromosome pairs that provide genetic information from both parents. This is in contrast to haploid cells, like gametes, which carry only one set of chromosomes. The diploid state supports genetic diversity when sperm and egg fuse during fertilization, restoring two sets of chromosomes in the zygote. The other terms describe reproductive processes, not chromosome count: estrus is a reproductive phase signaling readiness, gestation is the period of pregnancy, and lactation is milk production after birth.