Chromosomes and genes are indeed related, but they differ in some key ways. Let's analyze the options you've provided:
A. They both code for a single protein - This is not correct. A gene typically codes for a single protein (or sometimes more than one through processes like alternative splicing), but a chromosome is a larger structure that contains many genes along with other DNA sequences.
B. They both contain genetic material - This is true. Both chromosomes and genes are made of DNA, which contains the genetic instructions for the development and functioning of living organisms.
C. They are both part of DNA - This is somewhat misleading. While chromosomes are made of DNA, genes are specific sequences of DNA within chromosomes. So, it might be more accurate to say that genes are parts of the DNA that make up chromosomes.
D. They were both found on chromatids - This could be partially true, depending on the context. Chromatids are the two identical halves of a duplicated chromosome, and both genes and chromosomes are present on chromatids.
From this analysis, the best answer to illustrate how chromosomes and genes are related is B. they both contain genetic material.