A child’s traits come from a combination of genetic information inherited from both biological parents and influences from the environment. Genes help shape characteristics such as blood type, eye color, height, and susceptibility to certain diseases, but inheritance is rarely as simple as receiving a single gene that determines a single visible trait.
To understand how characteristics pass from parents to children, it helps to start with the basic units of heredity: DNA, genes, chromosomes, and genetic variants.
What is a genetic trait?
A genetic trait is a characteristic influenced by information encoded in DNA. Some traits are relatively straightforward to inherit, while others result from the combined effects of many genes and environmental factors.
Examples include:
- Blood type
- Certain inherited disorders
- Some aspects of eye and hair color
- Natural variation in height
- Certain physical features
- Differences in how the body processes particular substances
A trait can be influenced strongly by genetics without being determined entirely by genes. Height, for example, has a substantial genetic component, but nutrition, health, hormones, and other environmental factors also affect how tall a person becomes.
It is also important to distinguish a trait from a gene. A gene is a segment of DNA that contains biological instructions or helps regulate how cells function. A trait is the observable or measurable characteristic that results from genetic and environmental influences.
How DNA carries inherited information
DNA, or deoxyribonucleic acid, is the molecule that stores genetic information in cells. It is organized into long structures called chromosomes.
Most human cells contain 46 chromosomes arranged in 23 pairs. One chromosome of each pair usually comes from the mother and the other from the father. The exception is certain reproductive cells, which contain 23 chromosomes rather than 46.
Genes are located along chromosomes. Different versions of a gene are called variants or, in traditional genetics terminology, alleles. These variants can contribute to differences between people.
For example, people have genes involved in the biological processes that influence pigmentation, but variations in those genes can contribute to differences in skin, hair, and eye pigmentation.
What children inherit from each parent
A biological child receives roughly half of their nuclear DNA from each biological parent.
The process begins with specialized reproductive cells called gametes: eggs and sperm. Unlike most body cells, gametes contain one copy of each chromosome rather than chromosome pairs. When an egg and sperm combine during fertilization, the resulting cell receives one chromosome from each parent for each chromosome pair.
This means a child does not receive an identical half of either parent’s genetic material. Instead, each parent passes on a particular combination of their genetic variants.
That combination is shaped by meiosis, the process that produces eggs and sperm. During meiosis, chromosome pairs are separated, and segments of chromosomes can exchange genetic material through a process called recombination. As a result, the genetic material passed to a child is a new mixture of the parent’s chromosomes.
This is one reason siblings can have noticeably different characteristics even though they have the same two biological parents.
Dominant and recessive inheritance
One of the simplest inheritance patterns involves dominant and recessive variants.
For some genes, a person has two copies of a gene—one inherited from each biological parent. A dominant variant can influence a trait when only one copy is present, while a recessive variant generally influences the trait only when a person has two copies of that particular variant.
Consider a simplified example involving a hypothetical recessive condition. If both parents carry one copy of the relevant variant but do not have the condition themselves, each child has an independent chance of inheriting two copies and being affected.
This does not mean that dominant traits are necessarily more common, stronger, or better than recessive traits. “Dominant” and “recessive” describe how particular genetic variants interact in determining a phenotype; they do not describe the overall importance or quality of a trait.
Many real human characteristics do not follow a simple dominant-recessive pattern.
Some traits involve multiple genes
Many characteristics are polygenic, meaning they are influenced by many genes.
Height is a familiar example. Hundreds or more genetic variants can contribute to differences in height, with each variant generally having a relatively small effect. Environmental influences also matter.
Other complex characteristics, including many aspects of metabolism and susceptibility to common diseases, can similarly involve numerous genetic variants interacting with one another and with environmental conditions.
This explains why parents cannot reliably predict a child’s exact height, appearance, or many other characteristics simply by looking at their own traits. A child inherits a particular combination of variants, and the resulting biological effects can be complex.
Genes do not always act independently
Genetic variants can influence one another. A variant in one gene may affect how another gene functions, and some genes regulate the activity of other genes.
The observable result of genetic information is called the phenotype. The collection of an individual’s genetic variants is their genotype. Phenotype is not simply a direct readout of genotype; it can also reflect development, environment, and biological processes that occur throughout life.
For instance, two people can carry the same genetic variant but show different characteristics because other genes or environmental factors influence how that variant affects their bodies.
Why children resemble their parents but are not identical to them
Children often resemble their biological parents because they inherit genetic variants from them. But inheritance involves combinations rather than photocopies.
During the formation of reproductive cells, chromosomes are shuffled through chromosome segregation and recombination. Each parent therefore produces genetically varied eggs or sperm. Which particular egg and sperm participate in fertilization also matters.
A child may inherit a combination of variants that produces a characteristic strongly resembling one parent, another combination that resembles the other parent, or a mixture that looks different from either.
Siblings likewise inherit different combinations of their parents’ genetic material. Identical twins are an important exception: they arise from the same fertilized egg and therefore begin with essentially the same nuclear DNA, although biological differences can develop between them over time.
What makes a trait inherited versus environmental?
A trait can be influenced by both heredity and the environment.
Genetic inheritance can affect a person’s biological potential, while environmental conditions can influence how that potential develops. Nutrition, physical activity, exposure to certain substances, infections, medical conditions, and other experiences can affect biological traits.
The relative contribution of genes and environment also varies by trait and by population. Heritability is a statistical measure used by geneticists to describe how much variation in a particular trait, within a particular population and environment, is associated with genetic differences.
Heritability does not mean that a particular percentage of one person’s trait is “caused by genes.” A highly heritable trait can still be influenced by environmental changes, and a trait with substantial environmental influence can still have an important genetic component.
What are mutations and genetic variants?
A genetic variant is a difference in DNA sequence. Variants can arise through changes in DNA and can also be passed from parents to children.
Some variants have little or no detectable effect. Others influence physical characteristics, biological functions, or the risk of developing particular conditions. A smaller number can directly cause genetic disorders when they affect genes or regulatory regions in ways that disrupt normal biological function.
Not every genetic change is inherited from a parent. Some arise during a person’s development and are present only in certain cells or tissues. These are called somatic variants. Variants present in eggs, sperm, or their precursor cells can potentially be passed to future generations.
How genetic disorders can be inherited
Genetic conditions can follow several inheritance patterns.
Some are caused by variants in a single gene. Others result from changes involving chromosomes or from the combined effects of multiple genes and environmental factors.
A condition can be inherited as:
- Autosomal dominant: one altered copy of a relevant gene can be sufficient to cause the condition.
- Autosomal recessive: a person generally needs two altered copies to develop the condition.
- X-linked: the relevant gene is located on the X chromosome, producing inheritance patterns that differ between males and females.
- Mitochondrial: certain genetic conditions result from variants in mitochondrial DNA, which is generally transmitted through the egg.
These patterns describe common mechanisms, but individual genetic conditions can have more complicated inheritance. A person can also carry a disease-associated variant without developing the associated condition, depending on the specific disorder and variant.
Why family history matters
Family history provides clues about inherited risk because relatives share some genetic material. A pattern of a condition appearing repeatedly among close biological relatives can indicate that genetic factors may contribute to it.
But family history is not a guarantee that someone will or will not develop a condition. Relatives can share environmental exposures and behaviors as well as genes, and some genetic variants have effects that depend on other biological or environmental factors.
For this reason, genetic risk is best understood as probability rather than destiny in many circumstances.
What about characteristics that appear to skip a generation?
A trait can appear to “skip” a generation when genetic variants are passed along without producing an obvious characteristic in one generation and then contribute to a phenotype in a later generation.
Recessive inheritance is one way this can happen. A person may carry a recessive variant without showing the associated trait and pass it to a child. If the child receives another relevant copy from the other biological parent, the associated condition or characteristic may become apparent.
Traits can also seem to skip generations for more complicated reasons, including polygenic inheritance and differences in how strongly genetic variants are expressed.
The idea of a trait simply being “hidden” for one generation therefore works only for some inheritance patterns and should not be treated as a general rule.
Can parents pass traits they acquired during life to their children?
Most changes that occur in a person’s body during life are not passed genetically to their children. For example, gaining muscle through exercise or developing a scar does not normally alter the DNA in eggs or sperm in a way that transmits those acquired characteristics.
What can be inherited genetically is information present in the reproductive lineage. There are also biological mechanisms through which environmental conditions can influence gene regulation, including epigenetic processes. Some epigenetic effects can persist across cell divisions, and in certain organisms and circumstances effects can extend across generations. However, this is different from inheriting an acquired physical characteristic in the straightforward sense often implied by the phrase “inheritance of acquired traits.”
How sex chromosomes affect inheritance
Humans typically have one pair of sex chromosomes in addition to 22 pairs of autosomes. Most females have two X chromosomes, while most males have one X and one Y chromosome.
Eggs normally carry an X chromosome. Sperm can carry either an X or a Y chromosome. The combination formed at fertilization typically determines whether the resulting embryo has XX or XY chromosomes, although variations in sex chromosomes and biological sex development also occur.
Genes on the X chromosome can therefore follow distinctive inheritance patterns. For example, an X-linked recessive condition can affect males and females differently because males typically have only one X chromosome.
Why genetic traits are more complicated than simple family resemblance
The basic principle is straightforward: biological parents transmit genetic information to their children. The complexity comes from what happens after that information is combined.
A child’s characteristics can depend on the specific genetic variants inherited from each parent, interactions among genes, how genes are regulated, and environmental influences during development and throughout life. Some traits are largely shaped by a single gene, while many common characteristics emerge from the combined effects of numerous genetic factors.
Genetic inheritance therefore explains both sides of family resemblance: why children share characteristics with their parents and relatives, and why every child can still be biologically distinct.