Final answer:
The statement that incest will definitely lead to a genetic defect is false; while incest increases the risk of passing on deleterious mutations that can lead to defects, it is not guaranteed.
Step-by-step explanation:
The statement 'Incest will definitely lead to a genetic defect' is false. Incest, or the mating of closely related individuals, can increase the probability of offspring inheriting rare recessive genetic mutations from both parents, which can lead to harmful phenotypes or genetic defects. However, it is not a certainty that genetic defects will occur just that the risk is increased due to the higher chance that both parents will carry the same recessive alleles.
Inbreeding can indeed bring together deleterious mutations that, when combined, lead to harmful outcomes. Nonetheless, not all instances of incest result in genetic defects, and not all defects are due to incestuous relationships. It is a complex interplay of genetics, inheritance patterns, and chance.