PUNNETT SQUARES: QUESTION 5 Tay-Sachs disease is caused by a recessive lethal allele, meaning that individuals that are homozygous recessive (tt) will have the disease and die before they are able to have offspring. Two parents that are heterozygous (T) carriers for Tay-Sachs want to have children. What are the chances that their children will get Tay-Sachs disease?