Teacher Version

 

Name: ____________________________    Date: ________________
 

Exploration of Human Species:   A computer simulation of the classic introductory high school activity in human genetics.

GenScope Files:  Human



Now that you have had time to learn about GenScope tools and the Dragon species, it's time to look at a few common Human traits and figure out the rules governing their inheritance.  Although these traits are shown on specific chromosomes, you should be aware that the actual sites for the genes is unknown at this time.  In other words, we just made ╬em up!  But the mode of inheritance of these traits is known and has been integrated into the GenScope program.

To begin, start GenScope with the Human species file.

1.       Look at some of the traits.  Click on the magnifying glass at the ORGANISM level.  Hold your cursor over the spots on the human figures.  These spots are "hot spots" - which means that when you place the magnifying glass on top of one of the circles, you will get a picture of what the trait looks like.  Examples:  an enlarged picture of a cheek, a thumb, and earlobe, a chin or a hairline will appear.

The student, using the magnifying glass tool, clicks on each of the hot spots and sees the picture of the trait. S/he can then use the chromosome tool to find the chromosome that carries the allele for that trait and either change the allele to determine which is dominant or recessive, or can go to the pedigree window and cross the male and female to determine dominance, etc. Once the chart is filled out, the rules can be derived.


2.       Your job is to figure out how each trait is inherited.  You can use the chromosome tool if you like to explore.  Fill out the table below with the alleles for each trait.
 
 
 

Trait Homozygous Dominant (TT) Heterozygous (Tt) Homozygous recessive (tt)
Widow's Peak      
Dimples      
Ear lobes      
Cleft Chin      
Hitchhiker's Thumb      
Polydactyly (extra fingers)      

  Now, using the information that you have gathered and put in the above table, write a rule for how each of the traits is inherited. For example, if you were talking about the wings trait in dragons, the rule for wings would be W_ (meaning WW or Ww) is "Has no wings" and ww is "Has wings". Wingless (has no wings) is dominant to wings.
  1. Widow's Peak:
 

2. Dimples:
 

3. Ear lobes:
 

4. Cleft Chin:
 

5. Hitchhiker's Thumb:
 

6. Polydactyly (Extra digit):
 
 

Were any of these traits sex-linked?

How do you know?

The student, by this time has had lots of practice in going from phenotype to genotype, and determining which allele is dominant or recessive.  The hard part of this exercise to derive the rule, that is, to generalize from the particular.  Each of the traits will have its own rule which they must derive and write in the appropriate place.

Having dimples, polydactyly, a widow's peak and unattached ear lobes are dominant traits.  Having a cleft chin, or a hitchhiker's thumb are recessive traits.  Most beginning genetics students think that having a trait means that the allele for that trait is dominant.  They have trouble with this exercise because the reality goes against their intuituon.

The question about sex-linkage might upset them:  Discussions about sex-linkage have concentrated on figuring out how it works, not how you know the trait is x-linked.  The first thing the student will do to answer this question will be to look at the chromosomes with the chromosome tool in order to determine if the gene is, indeed, on the X chromosome.  But this is not how you "know" if it is x-linked in the real world.  S/he should be encouraged to try crossing two individuals with the trait to check on the distribution of the allele in the population.  A discussion of probability might be appropriate here, also.

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