We began with three claims to explain why there was variation among the offspring for silk flexibility:

As you can see, we eliminated Claim 2 because we saw that each offspring gets an equal number of genes from each parent. We’ll use the reasoning tool below to decide between Claim 1 and Claim 3.

Review the Family Tree diagram carefully, paying special attention to the spiders’ combinations of gene versions. Use the diagram to help you complete the reasoning tool below.

Based on what we just read, we can safely eliminate claim 1 (none of the spiders have a “new” gene version). If the offspring were having mutations, we would expect to see new gene versions that neither parent had. (Also, mutations *rarely* have an impact on traits).

To conclude our study of these spiders, we’ll write a summary of how we know Claim 3 is correct.