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(A) Hanging earlobe, (B) Attached earlobe
John Burke High School

Solve the Genetic Puzzle!

Are your earlobes free hanging or attached to your head?

Some people have earlobes than hang, and some people don’t. The gene for free hanging earlobes is dominant, and the gene for attached earlobes is recessive. That means that you have free hanging earlobes if you inherited the gene for it from at least one of your parents meaning that your genotype is “EE” (both genes for free-hanging lobes) or “Ee” (one gene for free hanging lobes). However, you have attached earlobes if you inherited genes from both parents that give instructions for attached lobes (“ee”).

Can you figure out these people’s genotypes (what the genes are) based on the phenotype information (whether or not they have free hanging lobes) and genetic relationships described below?

Solve the puzzle!

Clues:

  • Mary is the only one in her immediate family who has attached lobes.
  • Both of Mary's parents have free hanging lobes.
  • Mary's brother Fred also has free hanging lobes.

Questions:

1. If Mary has attached lobes, what must her genotype be? (Hint: Genotypes are described with two upper- and/or lowercase letters. Let's use the letter 'e' for this puzzle.)

2. If both Mary’s parents have free hanging earlobes, but they had a daughter who has attached lobes, what must their genotypes be?

3. What are the possible genotypes for Fred, Mary’s brother? Is it possible to identify his exact genotype? Why or why not?

Scientists use a square called a Punnet Square to help describe the possible genotypes of offspring based on the parents known genotypes. Draw a Punnet Square like the one below. Fill in the genotypes of both parents that you figured out in #2 above. Then, in each yellow square,
combine the mother's gene of that column and the father's gene from that row so see possible combinations of offspring genes. That will help you figure out the possible genotypes for Fred.


Last modified April 13, 2004 by Lisa Gardiner.

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