Answer the following question: Fact 1: Genes that are located on the same chromosome are called linked genes. Fact 2: Thousands of genes are linked together in a chain to form chromosomes. Given the two facts above, genes that are located on the same chromosome are chained together by the what?

Choices:
1). forces;
2). light energy;
3). voltage;
4). thousands;
5). A computer;
6). sun's heat;
7). photons;
8). Acids;
Answer:
4).