Final answer:
The embryonic stage is a critical period of development in which genetic and environmental agents are most likely to cause birth defects. Alcohol exposure during specific periods within this stage can lead to facial abnormalities associated with fetal alcohol syndrome. Overall, such exposures are likely to have harmful effects on the developing embryo.
Step-by-step explanation:
The embryonic stage is the time when genetic and environmental agents are most likely to cause birth defects. It is a critical period of development and lasts from implantation until the eighth week after fertilization. During this stage, the embryo undergoes significant growth and changes, including the formation of organs and the main development of the sex organs.
Research has shown that exposure to harmful agents during specific periods within the embryonic stage can have devastating effects. For example, alcohol exposure limited to day 19 or 20 of gestation can lead to significant facial abnormalities associated with fetal alcohol syndrome. The brain also has sensitive periods during which it is most susceptible to the teratogenic effects of alcohol.
Overall, genetic defects or harmful environmental exposures during the embryonic stage are likely to have harmful effects and may cause miscarriage or birth defects in the developing embryo.