Two sets of parents who have children with Down syndrome meet at a clinic. The Walters know that their son has trisomy 21. The Benders, however, have...

Two sets of parents who have children with Down syndrome meet at a clinic. The Walters know that their son has trisomy 21. The Benders, however, have two affected children and Mrs. Bender has had three spontaneous abortions. Explain why the Benders probably should be more concerned about future reproductive problems than the Walters?