Applying the Laws of Inheritance

When a baby is born, we cannot help but look for family resemblances. Shared traits can be a joy or a burden, but they are often inescapable. We still often think of an offspring as a blend of its parents, but from the work of Gregor Mendel, we now know it is not so simple. Mendel is known as the father of genetics, but during his life he was relatively unknown as a scientist.  He was a monk who studied mathematics, probability, and physics, but his interest in the natural world led him to conduct studies on pea plants. His mathematical mind and meticulous application of the scientific method allowed him to discover hidden patterns of inheritance.  Unfortunately, the significance of his work was not understood until the 20^th Century.      

Today, biology teachers explain Mendel’s laws of inheritance in conjunction with meiosis and fertilization. The first law, The Law of Segregation, states that alleles of traits separate into gametes during meiosis, so that each gamete receives only one copy. This creates haploid gametes from a diploid germ cell. The second law, The Law of Independent Assortment, states that alleles arrive in gametes independently from one another. Students apply these laws and rules of probability using Punnett Squares. I use an interactive white board as I explain to my students that during meiosis the alleles separate independently into gametes.  This is why we put only one corresponding letter on the outside of each box of a Punnett Square. Then the traits are combined into potential offspring, which is represented with the inside of the square. All of these events are random, so an understanding of mathematical probabilities is essential. 

Next, my students apply Mendelian Genetics to humans in a lab simulation. I have students pair up as future parents. Each parent receives a coin and is told that they are heterozygous for every human trait. They receive handouts explaining each facial trait, from a widow’s peak to eye color. For every trait, they flip their coins to determine which alleles their ‘baby’ receives. Heads gives the baby a dominant allele, while tails represents a recessive allele.  During the class period, each pair works through the crosses and writes down the genotypes and phenotypes of their ‘offspring’. At the end of the lab, students draw their results and we display them for the class to see. Students have fun flipping coins and exclaiming over the beauty or ugliness of their ‘child’. Sometimes they even forget that they are learning and applying genetic principles!

This activity helps even reluctant students firmly understand Mendelian Genetics. To make it more challenging, once students understand the basic monohybrid cross, I introduce dihybrid and even trihybrid crosses. The more traits you consider at once, the more complicated the cross. This quickly shows students how two parents can have such vastly diverse offspring.  We also discuss how every ‘parent’ in our lab simulation had the same genotype, yet every child produced was very different. You can also discuss how this ties into evolution and natural selection. Through these activities, and those listed below, you can help your students understand basic Mendelian Genetics.

Medelian Genetics Activities and Lessons:

Fundamentals of Genetics  

Students engage in activities on Mendelian Genetics using an interactive web-based tutorial. They define, calculate, and explain various aspects of Mendalian Genetics.

Variations on a Human Face Lab  

Students gain an application level understanding of probability, symmetry, and ratios and rates that exists in one's everyday environment relative to human genetics.

A Mendel Seminar  

Students analyze Gregor Mendel's discovery of a process of biological evolution. They also explore how recessive and dominant traits are passed from one generation of living organisms to the next. This lesson involves environment diversity and heredity.