Throughout this chapter, you will be introduced to important key terms that will help deepen your understanding of human development.

• Advanced maternal age: refers to a pregnancy in which the mother is 35 years of age or older. The term is used because there are certain increased risks associated with pregnancy at this age.
• Biological sex: refers to the biological differences between males and females, such as differences in reproductive organs, hormones, and chromosomes. However, gender is not the same as biological sex.
• Chemoattractant: a chemical signal that attracts cells or organisms towards its source. Chemoattractants can be produced by cells or tissues in the body, or they can be found in the external environment.
• Chromosomes: thread-like structures that carry genetic information in the form of genes, which are made up of DNA. They are found in the nucleus of most cells in the body and exist in pairs, with one chromosome in each pair inherited from each parent.
• Chromosomal abnormality: a condition in which there is a change in the number or structure of chromosomes. Chromosomal abnormalities can occur due to errors during cell division, exposure to certain chemicals or radiation, or inherited genetic mutations.
• Cisgender: a term used to describe people whose gender identity matches the sex they were assigned at birth.
• Classism: prejudice or discrimination based on social class or economic status including factors such as wealth, income, education, and occupation.
• Differential susceptibility: some people may be sensitive to negative environmental influences, such as adverse childhood experiences, while others may be more resilient and able to cope with such experiences.
• Dominant gene: a genetic trait that is expressed when only one copy of the gene is present in an individual’s DNA. This means that if a person inherits a dominant gene from either parent, they will display the trait associated with that gene.
• Epigenetics: epigenetics refers to modifications to the genome that do not involve changes to the DNA sequence itself but can still be passed down to subsequent generations. Epigenetic modifications can occur in response to environmental factors such as diet, stress, and exposure to toxins.
• Gender: refers to the socially constructed roles, behaviors, and expectations that are associated with being male or female. Gender is a complex concept that includes biological, social, cultural, and psychological factors, and it can vary across different cultures and time periods.
• Genotype: an individual’s complete set of inherited genes, representing the genetic makeup of an organism. It is the genetic information that is passed down from an individual’s parents and determines many of their physical and behavioral traits.
• Geriatric pregnancy: an outdated term that refers to a pregnancy in which the mother is 35 years of age or older. The term is used because there are certain increased risks associated with pregnancy at this age.
• Heterozygous: refers to an individual having two different alleles, or versions of a gene, at a particular genetic locus (position on a chromosome). This means that the individual inherited different forms of the same gene, one from each parent.
• Homozygous: refers to an individual having two identical alleles, or versions of a gene, at a particular genetic locus (position on a chromosome). This means that the individual inherited the same form of the gene from both parents.
• Implicit bias: refers to attitudes or stereotypes that influence our understanding, actions, and decisions in an unconscious or automatic way, often without our awareness or intention. These biases can be positive or negative and can be based on characteristics such as race, gender, age, ethnicity, sexual orientation, or other factors.
• Mitosis: the process of cell division in which a single cell divides into two identical daughter cells. It is a vital process for growth, repair, and replacement of cells in the body.
• Meiosis: cell division that occurs only in specialized cells called germ cells. Unlike mitosis, which produces two identical daughter cells, meiosis produces four genetically diverse daughter cells, each with half the number of chromosomes as the original cell. Meiosis is important for sexual reproduction, as it produces gametes (sperm and egg cells) with genetic diversity.
• Nature vs. nurture: a long-standing debate in psychology and other related fields that concerns the relative influence of genetic inheritance (nature) and environmental factors (nurture) on the development of human traits and behaviors. Today, most researchers agree that both nature and nurture are important factors in shaping human development, and that the interaction between genes and the environment is complex and dynamic.
• Phenotype: observable traits or characteristics of an organism, resulting from the interaction of its genetic makeup (genotype) with the environment. The phenotype includes all physical, behavioral, and physiological characteristics of an organism, ranging from its height, eye color, and hair color to its cognitive abilities, personality, and susceptibility to diseases.
• Plasticity: the ability of an organism or system to adapt to changes in its environment or experiences. In neuroscience, plasticity refers to the brain’s ability to change and adapt in response to experiences, such as learning and memory.
• Polygenic: a trait or characteristic that is influenced by multiple genes, rather than being controlled by a single gene.
• Racism: set of beliefs that certain racial or ethnic groups are inherently superior or inferior to others based on their perceived physical, cultural, or other differences. Racism can manifest in individual attitudes and behaviors, as well as in institutional policies and practices.
• Recessive gene: a type of gene that is only expressed or observed in an individual’s phenotype when two copies of the gene are present, one inherited from each parent.
• Social Determinants of Health: the social, economic, and environmental conditions in which people are born, grow, live, work, and age that can have a significant impact on their health and well-being. These factors can include things like poverty, discrimination, access to healthcare, education, employment, and housing.
• Teratogens: substances, agents, or factors that can cause developmental abnormalities or malformations in a developing embryo or fetus. These substances can be physical agents, such as radiation or heat, chemical agents, such as drugs or alcohol, or infectious agents, such as viruses or bacteria.
• Transgender: a term used to describe people whose gender identity differs from the sex they were assigned at birth.