Question

Tom has 46 chromosomes and Tracy has only 45 chromosomes, both are phenotypically wild-type. Their first boy Lucas has only 45 chromosomes and has a wild type phenotype, whereas their second son Evan has 46 chromosomes and he has Down syndrome.

1. Draw chromosomes 15 and 21 for each of the family members and explain their genotypes and phenotypes

2. Tracy is 24 years old and pregnant again. Should she be concerned about having another child with Down syndrome. Explain

Tom and Tracy met John and Jane (now 35 years old) in a support group for parents of children with Down syndrome. John and Jane's daughter has a genotype of 47,+21. Jane is also pregnant again.

3. Which couple should be more concerned about having a child affected with Down syndrome and why?