Practice Genetics: Sex Linked Genes


Students learn basic Mendelian genetics by crossing traits from fruit flies and pea plants.  In this extension, students can practice doing crosses that involve sex-linked traits, where the alleles are located on the X chromosome  which affects the pattern of inheritance.  

This worksheet is designed for beginning biology students, as it provides in most cases, the genotypes for the crosses are provide or students are given a model to use to determine the genotypes of the cross.   The problems get progressively harder.

This set includes three problems on fruit fly eye coloration, such as a white-eyed female  (X r X r)crossed with a red-eyed male (X R Y).  The set then looks at how hemophilia is inherited in humans, and reinforces the concept of a “carrier” when dealing with human diseases.  Students will be able to see that females who are carriers (X H X h ) will only pass the disorder to their sons.

Finally, students examine the inheritance of coat color in calico cats which are sex-linked and codominant (X B X R).

Generally when I assign this worksheet, I circulate among the class and help students.  With freshman, I find great diversity in how quickly students grasp these concepts.   I don’t normally grade this worksheet, as I use it more as practice and to determine which students need extra help.   I will usually put a LIKE stamp on completed worksheets, this little stamp has served me very well in doing quick checks and motivating students.

like stamp

Grade Level:  8-10
Time Required:  15-20 minutes

HS-LS3-3 Apply concepts of statistics and probability to explain the variation and distribution of expressed traits in a population.