Lesson 4: Dihybrid Crosses
WHAT ARE DIHYBRID CROSSES?
A dihybrid cross is a genetic cross which demonstrates the transmission of two independent trait (each trait made of two alleles) from both parents to offspring's. A dihybridhybrid cross can be used to estimate the probability of an offspring carrying a variation of each trait independently of each other.
MINDS ON:
Figure 11B
To get the class started, try using these flashcards to review content from previous lessons related to genetics, inheritance, and monohybrid crosses. Quizlet is an outstanding application which can we used on all electronic platforms including smartphones, tablets, and laptops, which allows users to set up a deck of flashcards to teach or review material. Users can then use the deck they have created to play matching games, quizzes, flashcard reviews, learning exercises, and practice spelling.
This minds on activity takes students through the process of understanding how monohybrid and dihybrid crosses can be used to predict the probability of an offspring inheriting a particular trait. Using the two faces of a penny (which represent the two alleles of a gene), students get to visually experiment on the probability of an offspring inheriting a single trait. Then using a punnett square and their knowledge from the last lesson, students can compare the theoretical probability to the actual. Using a penny and a dime, the same methods are followed to understand the pattern of inheritance of two traits which are independent of each other. questions such as What is probability? What does random mean and how does it apply to genetics? How does probability relate to the Punnett Square and the offspring that are shown? are constantly being reviewed during this activity.
PEDAGOGY:
To start the pedagogy portion of this lesson, reviewing content that students are still not comfortable with could be beneficial. In addition, Using a PowerPoint to teach students about the variability that independent assortment allows is important before moving on the the following activity. The video below reviews the process of independent assortment during meiosis, to demonstrate the variation it can cause in a population.
Figure 12B
Dragon genetics is an activity teachers can use to teach the process of independent assortment and the pattern of inheritance of multiple genes. This activity uses the process of meiosis and inquiry, to allow students to understand how independent assortment affects what type of alleles are present in the production of gametes. Using pop-sickle sticks which represent chromosomes,and the faces of each stick representing different alleles, students are allowed to construct their own knowledge of how genes on different chromosomes influence the traits the offspring with contain for multiple traits. An similar activity for linked genes is also incorporated for differentiation.
CONSOLIDATION:
A great way to consolidate this lesson, as well as all the previous lessons on Mendelian genetics is to use a jeopardy game. As teachers, you can give students the chance to create their own jeopardy game on the content they have learned thus far. Using template freely available of the internet, students can create questions around definitions, concepts, problem solving, and general knowledge, which they can then use for reviewing purposes. Attached below is a jeopardy game similar to a one students could create, which can also be used as a review. It covers content around monohybrid crosses, dihydbrid crosses, laws of inheritance, key definitions, practice examples.
| jeopardypunnettsquares.ppt |
Another fun way to end the lesson is to use the link provided, to allow students to play around with genes that determine eye color. Using the principles they have learned about multiple gene inheritance, students get the chance to determine the probability of what the color of their children's eyes would be based on the alleles their parent, themselves, and their mate carries. This activity can also be used to build handouts around as a fun way to student independent assortment at home.
Figure 13B
