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Block 1 Unit 2 Prenatal Development - Genetics, Environment Influence and Hazards of Development

1. Define the prenatal period.

The prenatal period is the time from conception to birth, approximately nine months long. It is the first and most important period of development in the lifespan. During this period, the individual's heredity and sex are determined, and conditions in the mother's body can disturb the pattern of prenatal development.

2. Elaborate on the stages of prenatal development.

The prenatal period is divided into three stages:

• Period of the Zygote: This stage lasts from fertilisation to the end of the second week. It begins when the sperm fertilises the egg, forming a zygote with 46 chromosomes. The zygote rapidly divides, but appears much like an unfertilised egg initially.
• Period of the Embryo: This stage spans from the end of the second week to the end of the second lunar month (approximately eight weeks). During this critical period, the embryo's cells multiply and take on specific functions through tissue differentiation. The developing foetus is highly susceptible to damage from external sources, such as viral infections, radiation, and poor nutrition. Key developments include the formation of the heart, brain, spinal cord, and gastrointestinal tract.
• Period of the Foetus: This stage extends from the end of the second lunar month until birth. The foetus undergoes significant growth and development, with various organs and systems maturing. Reflexes begin to appear and develop. The foetus prepares for independent life by storing essential nutrients and developing respiratory movements. The full term foetus is considered to be at 38 weeks.

3. What are the two stages in which male sex cells go through?

Before producing new individuals, male sex cells go through two preliminary stages: maturation and fertilisation.

4. What are the three stages in which female sex cells go through?

Before producing new individuals, female sex cells go through three stages: maturation, ovulation, and fertilisation. Ovulation is when a mature ovum is released during the menstrual cycle.

5. Define the genetic influences on the prenatal period.

Genetic influences during the prenatal period are defined by the combination of genetic material from both the mother and father. Half of a person's genetic material comes from the father and half from the mother. This material comes together when the sperm fertilises the egg, creating a unique genetic combination. This combination is responsible for the individual's traits, differentiating them from their parents, while also showing similarities. Hereditary factors are essential for prenatal development, serving as the foundation for later growth.

6. How can environmental influences affect the development of the infant?

Environmental influences can significantly affect prenatal development, beginning at conception. The foetus is influenced by the larger environment of the mother's uterus, which is affected by the mother and her world. 

These influences include:

1. Mother's Diseases: Diseases like rubella and cytomegalovirus can be particularly dangerous, leading to stillbirth, deafness, prematurity, miscarriage, and heart defects. Mumps, polio, and influenza may also have teratogenic effects. Diabetes and blood poisoning can also affect the foetus, potentially causing premature birth or smaller-than-average babies.
2. Drugs and Chemicals: Alcohol, antihistamines, aspirin (in excess doses), barbiturates, heroin, lead, quinine, thalidomide, insulin (large doses), and tobacco can negatively impact the developing embryo and foetus, potentially causing physical abnormalities, internal organ issues, growth retardation, and cognitive deficits.
3. Maternal Stress: Maternal stress can affect foetal development through the autonomic nervous system and hormones that can pass through the placenta, and can lead to issues such as motor depression in newborns.
4. Other Factors: Radiation, X-rays, and other external factors can also pose risks to the developing foetus.

Important Points

1. Development before birth takes place in three stages or periods.
2. A female has XX chromosomes and a male has an X and a Y chromosome.
3. X and Y chromosomes are the sex-determining chromosomes. (True)
4. The prenatal period is nine calendar months.
5. A woman who is suffering from blood poisoning during her pregnancy frequently gives birth to a premature baby.
6. Cigarette smoking is associated with prematurity and low birth rate.
7. Radiation is responsible for damage to the foetus.
8. Abortion is a procedure to know the child's gender.
9. The mother is the only sole source of nutrition for the unborn child.