Activity 1-1 – Data on Human Traits

Introduction to Genotype, Phenotype, and Inheritance

Phenotype refers to the observable traits or characteristics displayed by an organism—such as eye color, blood type, or the ability to roll one’s tongue. Genotype, on the other hand, is the underlying genetic makeup that determines these traits. In essence, the phenotype is the product of both genotype and environmental interactions. For example, a person may have the genotype for tall stature, but poor nutrition during growth can result in shorter height—a clear demonstration of gene-environment interplay. In this lab, students will focus on traits that are primarily influenced by genetics to observe inheritance patterns.

Phenotype can be thought of as the "performance on stage", while genotype is the "script written backstage." Just like actors follow a script (with room for improvisation), organisms express physical and behavioral traits based on their genetic instructions—but those traits may also be influenced by the environment. For instance, let’s imagine two genetically identical seeds (same genotype). If one is planted in nutrient-rich soil with ample sunlight and water, while the other is planted in poor soil and receives little light, they will grow into very different plants—demonstrating different phenotypes despite sharing the same genotype. This is similar to how a child genetically predisposed to be tall may not reach their full height potential if malnourished during critical developmental years.

This interaction between genes and the environment is central to fields such as personalized medicine, where doctors tailor treatments based on a patient’s genotype while also considering lifestyle and environmental factors. For example, some individuals metabolize drugs like warfarin or codeine differently due to genetic variants in liver enzymes—an application of genotype-phenotype analysis in clinical settings.

The primary goal of this lab is to help students understand how certain human traits are inherited and to introduce them to bioinformatics tools used to study human genetic disorders. The activities are designed to build practical skills in identifying patterns of inheritance—such as autosomal dominant, autosomal recessive, and sex-linked traits—and to explore the real-world utility of online genetic databases like NCBI and OMIM. Ultimately, students will not only analyze their own traits but also research genetic diseases, obtain sequence data, and use BLAST to identify homologous sequences, deepening their understanding of genetics and molecular biology.

Modes of Inheritance: Autosomal and Sex-Linked Traits

Traits in humans are inherited according to well-established patterns, depending on where the gene responsible for a trait is located and whether the allele is dominant or recessive. These patterns help us predict how specific characteristics or genetic disorders may be passed from one generation to the next. The two major categories of inheritance that we will focus on are autosomal inheritance and sex-linked inheritance.

• Autosomal dominant traits are caused by genes located on the autosomes, which are the 22 pairs of chromosomes that do not determine sex. A trait is considered dominant if just one copy of the dominant allele—received from either parent—is enough to express the trait. This means that a person only needs one "strong" version of the gene for the characteristic to be visible. For example, having a widow’s peak (a V-shaped point in the hairline) is often cited as an autosomal dominant trait. If a child inherits the dominant allele from just one parent, they are likely to show the trait, regardless of the allele they inherits from the other parent.
• Autosomal recessive traits also involve genes on the autosomes, but in this case, both alleles must be the recessive form for the trait to be expressed. If an individual has only one copy of the recessive allele, they are considered a carrier and typically do not show the trait themselves. The trait is only observed when the person inherits the recessive allele from both parents. A classic example is attached earlobes, which are commonly used in educational settings to demonstrate autosomal recessive inheritance. If both parents are carriers, there is a 25% chance that their child will inherit two copies of the recessive allele and display the trait.
• Sex-linked traits are associated with genes located on the sex chromosomes, particularly the X chromosome. Since females have two X chromosomes (XX) and males have one X and one Y (XY), inheritance of sex-linked traits often differs between the sexes. X-linked recessive traits, such as red-green color blindness, are more commonly expressed in males. This is because males only have one X chromosome, so a single recessive allele on that X is enough for the trait to appear—there is no second X to potentially mask the effect. In contrast, females must inherit two copies of the recessive allele (one from each parent) to express the trait, which is less likely. X-linked dominant traits can affect both males and females but are often more easily transmitted from mothers to their children since mothers contribute one of their two X chromosomes to each child. The Y chromosome carries very few genes, so Y-linked inheritance is rare and usually involves traits passed strictly from father to son.

Understanding these different modes of inheritance—autosomal dominant, autosomal recessive, and sex-linked—is essential for predicting how traits may appear in families and populations. More importantly, these principles form the foundation for analyzing and diagnosing genetic disorders, many of which follow these same classic Mendelian patterns. Mastering this knowledge will help you not only understand your own inherited traits, but also begin to explore the genetic basis of human health and disease.

Activity 1-1: Collecting Data on Human Traits

This activity introduces students to foundational concepts in genetics through direct, observational data collection. Students will investigate common human phenotypic traits—physical characteristics that result from their underlying genotype (genetic makeup). These traits are examples of Mendelian inheritance, where a single gene controls the expression of a trait and follows predictable patterns (dominant vs. recessive).

By gathering data on themselves and their peers, students will begin to understand how often specific alleles appear in a small "population" (their class). For example, tongue rolling is often cited as a dominant trait. If 70% of the class can roll their tongue, this suggests a higher frequency of the dominant allele in this mini-population. However, students will also observe traits like attached vs. free earlobes, dimples, or widow’s peak—traits typically used in genetics education to model autosomal inheritance patterns. This activity is not only about counting traits; it's about visualizing gene frequency, inferring genotypes, and exploring what our genes say about us—even in a small population.

More importantly, it opens a fascinating question: Do the most common traits in a population match the traits we find most attractive or desirable? From an evolutionary and anthropological perspective, physical attractiveness is shaped by what traits were perceived as favorable for mating. Yet, this doesn't always align with dominant traits. For example, blue eyes are recessive but are often considered attractive in some cultures. Similarly, dimples (dominant) and freckles (sometimes recessive) are sometimes romanticized features. Students will reflect on whether the traits most commonly found in the class are also those considered most "attractive" or "desirable," and what this might say about sexual selection vs. natural selection. Imagine we’re studying a population to identify traits associated with perceived attractiveness. Evolution isn’t just about survival—it’s also about reproduction. In this light, the traits that become more common over generations may not only be “dominant” genetically, but also selected because of attractiveness or social preference.

Ask yourself:

• Are traits like dimples, widow’s peak, or eye color more common because they’re dominant or because they’re seen as attractive?
• Are there recessive traits that are still prevalent because they’re desirable (e.g., blue eyes)?
• If we view our class as a sample population, what traits do we find attractive—even if they’re not the most genetically dominant?

This exercise encourages you to reflect on how sexual selection (mate preference) may shape populations over time, sometimes in ways that contrast with pure Mendelian expectations. Dominance does not always equal desirability.

Table 1-1: Genetic Trait Survey