Understanding the laws becomes much easier for students if you give them visual examples. For instance, the Law of Segregation states that for each trait, organisms have a pair of genes, but only one of them is passed to offspring. Out of the two inherited alleles, the "dominant" gene prevails over the "recessive" one. To show how the law works, make flashcards of organisms with noticeable characteristics, such as dogs with white or brown fur, or different color tails, then stick the cards on a board. Write the pairs of genes for each characteristic below each flashcard -- using capitals for dominant genes and lower case letters for recessive ones -- and show students the possible characteristics of the offspring from different dog pairings.
The Punnett square was not devised by Gregor Mendel, but it shows the possible characteristics of offspring, based on parents' genes, in a comprehensible manner. The square resembles a Tic-Tac-Toe grid. Across the top row of the grid, should be the genes of one parent, such as "Yy," with those of the other parent on the leftmost column -- the top-left square is left blank. The rest of the squares contain the four possible combinations; remember that according to the Law of Segregation, only one gene is passed on, so you can only make two-letter combinations. The Punnett square also helps you explain Mendel's three-to-one ratio.
The Law of Independent Assortment is Mendel's second law and states that the segregation of one pair of genes is independent from the segregation of other pairs of genes. To help students understand this concept, make a drawing of the segregation process of several pairs of genes. Use different geometric shapes to depict each pair of genes, with a small and big square for eye-color genes, for example, and a small and big triangle for hair-color genes. Explain to students that since each pair segregates independently, the possibility of each shape "meeting" any other shape in the gamete is the same.
Encourage students to participate actively throughout the lesson. For example, instead of explaining the possible characteristics of the offspring of organisms depicted on flashcards, ask students to make a guess, based on the data you have provided. In addition, you can ask students to complete the Punnett square themselves. Such short and easy activities can help you grab the attention of students and ensure they have understood Mendel's laws.