Final answer:
The Fair Housing Act of 1968 was amended to include sex as a protected class in 1974, which prohibited gender-based discrimination in housing.
Step-by-step explanation:
The year the Fair Housing Act of 1968 was amended to add sex as a protected class is 1974. This act, originally intended to ban discrimination in the sale or rental of housing, was strengthened by the amendment, furthering the cause of equal rights. Subsequently, it became illegal to discriminate based on sex in housing decisions, protecting individuals from gender-based discrimination in real estate transactions, which was a significant step forward for the women's rights movement.