Q.Give two examples of teratogens and explain how they can affect prenatal development.

Teratogens are environmental agents that can cause deviations, abnormalities, or even death in a developing foetus; examples named in the chapter include maternal drug/alcohol/tobacco use and exposure to radiation such as X-rays. …

The prenatal period — the roughly 40-week stretch from conception to birth — is shaped jointly by the genetic blueprint a foetus inherits at conception and by environmental influences acting throughout pregnancy. Teratogens are specifically environmental agents that cause deviations in normal development, deviations that can lead to serious abnormalities or even death in the developing child, and the chapter names several concrete examples.

The first example is the intake of drugs, alcohol, and tobacco by a pregnant woman. The chapter specifically names marijuana, heroin, and cocaine as drugs that may have harmful effects on the foetus, alongside alcohol and tobacco use, noting that such intake during pregnancy may have harmful effects on the foetus and can increase the frequency of congenital (present-at-birth) abnormalities. These substances are able to cross from the mother's bloodstream to the developing foetus, interfering with the normal, genetically guided sequence of prenatal growth at a stage when the foetus is especially vulnerable to disruption.

The second example is radiation, such as X-rays, along with certain industrial chemicals found near industrial areas — the chapter states that these can cause permanent changes in the genes of the developing child. Because radiation and certain chemicals can directly damage genetic material, exposure during pregnancy carries a risk of altering the foetus's genetic blueprint itself, with effects that can be permanent. …