**Question:** A person showing two cell lines derived from one zygote is

A. Diploid
B. Haploid
C. Nephron-potential cells
D. Embryonic and fetal cells

**Core Concept:** Zygote is a single cell formed by the fusion of sperm and egg, containing a complete set of chromosomes (n = 46). After fertilization, the zygote undergoes cell division (meiosis or mitosis) to form a multinucleated embryo or fetus.

**Why the Correct Answer is Right:** The correct answer is D. Embryonic and fetal cells, because the zygote undergoes cell division (mitosis) to form a multinucleated embryo or fetus. During this process, the number of chromosomes remains constant (n = 46), which results in two different cell lines with different functions and developmental stages.

**Why Each Wrong Option is Incorrect:**

A. Diploid (n = 46) would imply only one cell line, not two.
B. Haploid (n = 23) is incorrect as it represents a single cell line with half the number of chromosomes, not two different cell lines.
C. Nephron-potential cells are cells that have the potential to develop into nephrons, the functional units of the kidney, but not related to the zygote or two cell lines.

**Clinical Pearl:** The presence of two cell lines demonstrates the importance of understanding the embryonic and fetal development, as well as the different functions and stages of these cell lines. This knowledge is crucial for interpreting karyotype variations, genetic disorders, and prenatal diagnosis.