Developmental psychologists consider the process of human development as it relates to physical, cognitive, and psychosocial development. This lifespan development is organized into different stages based on age. Prenatal development is the process that occurs during the 40 weeks prior to the birth of a child, and is heavily influenced by genetics.
There are three stages of prenatal development—germinal, embryonic, and fetal. Prenatal development is also organized into trimesters: the first trimester ends with the end of the embryonic stage, the second trimester ends at week 20, and the third trimester ends at birth.
Overview of Genetic Inheritance
Every person is made up of cells, each of which contains chromosomes. Chromosomes are genetic material that determines many things about a person, such as eye and hair color, biological sex, and personality traits. DNA, or deoxyribonucleic acid, is responsible for the transmission of genetic material. A mother and father’s DNA are passed on at the moment of conception.
A human being has a total of 23 pairs of chromosomes. The developing zygote gets half of its chromosomes from one parent and half from the other parent. The first 22 pairs of chromosomes are known as autosomes and determine things such as eye and hair color. The last pair, known as the sex chromosomes, determine a person's biological sex: females have two X chromosomes, while males have an X and a Y chromosome.
Gene Expression and Regulation
Gene expression is carefully regulated in every organism to allow the organism to adapt to differing conditions. The expression of genetic information in a given cell or organism is neither random nor fully pre-programmed. Genes can either be dominant or recessive, meaning they can either be expressed or hidden. Depending on the dominance of each chromosome that is inherited from each parent, the child may or may not show the inherited trait.
Gene regulation is the process by which cells differentiate. Among other things, it is the process in which a cell determines which genes it will express and when. Cell differentiation is a process by which a less specialized cell becomes a more specialized cell. For example, as a zygote develops, gene regulation changes some cells into brain cells and others into liver cells. Other cells will become the lining of the stomach, the intestines, and the sexual reproductive organs.
Mutation is when a sudden change in a segment of the DNA occurs. Some mutations of the genes can result in conditions such as Down Syndrome or Turner's Syndrome.
The Importance of Genetics in Human Development
Differences in gene expression—whether as a result of standard regulation processes or through mutation—are crucial to an individual's physical and psychological development. The exact extent to which genes, as opposed to an individual's environment, determine or influence psychological development is hotly debated; this controversy is known as the "nature-vs.-nurture debate." However, an individual's genetic makeup at the very least serves as a crucial baseline (which may then be mediated by the environment) for such characteristics as the ability to begin learning spoken language, such personality traits as a tendency toward aggressive versus submissive behavior, and risk levels for such diseases as alcoholism and addiction.
Before birth, a fetus has of course had limited opportunity to be shaped by its environment, beyond factors such as the mother's diet, substance use, and anxiety level. For this reason, genetics play a particularly important role in prenatal development.