Please construct a pedigree diagram of as many generations that you can.  You can estimate the genotype of missing family members.

Do not tell your family member you are trying to investigate if they taste a bitter flavor. Most people will anticipate and produce the flavor in their head. We call this a placebo effect. Our large brains get in the way when human testing is done. What you should do is tell your family member that you testing if they taste flavors not necessarily the “bitter” taste. Give them the control first and then give them the PTC test paper. 

Teach your family member what PTC is and record if your family member tastes the bitter flavor or not. Remember that PTC has Mendelian characteristics and this tasting test was used as a paternity test for many years!!

Paternity tests are done to determine the parents of children.

Because The Bitter Tasting Allele has Mendelian characteristics the genotype can be determined by the following phenotypes: 

1: If Family member taste the bitter flavor = homozygous dominant

2: If the Family member tastes the bitter flavor only a little bit = heterozygous

 Careful with this one.  This phenotype is hard to determine. So if someone tastes only a small amount of bitter taste give them the control again and test again to make sure.

3.  If the Family member does not taste the bitter flavor  = homozygous recessive.

Your pedigree diagram should use the same familiar format:

Try to determine what your missing family members genotype is based on your evidence from other related family members.

What type of pedigree did your family demonstrate?  

X – Linked recessive, X -linked dominant, Autosomal dominant, Autosomal recessive?

Please place your Pedigree in THIS shared doc!

*Remember that the ability to taste or not to taste is based on a working protein receptor of a proper 3 dimensional shape (based on the R-groups in the primary amino acid sequence) that allows the tongue to recognize the PTC chemical.  What are the evolutionary implications?

In 1931 Arthur Fox in Wilmington, Delaware, synthesized phenylthiocarbamide (PTC). Some researchers reported a bitter taste when entering his laboratory, while others, including Fox himself, experienced no such sensation. Fox hypothesized that the taste was due to PTC particles suspended in the air and that some people were able to taste the chemical while others were not.  In the early thirties is was understood that the tasting ability was hereditary and the ability to taste or not taste PTC was used in paternity tests.

Soon after its discovery, geneticists determined that there is an inherited component that influences how we taste PTC. Today we know that the ability to taste PTC (or not) is conveyed by a single gene that codes for a taste receptor on the tongue. The PTC gene, TAS2R38, was discovered in 2003.

There are two common forms (or alleles) of the PTC gene, and at least five rare forms. One of the common forms is a tasting allele, and the other is a non-tasting allele. Each allele codes for a bitter taste receptor protein with a slightly different shape. The shape of the receptor protein determines how strongly it can bind to PTC. Since all people have two copies of every gene, combinations of the bitter taste gene variants determine whether someone finds PTC intensely bitter, somewhat bitter, or without taste at all.

It has been suggested that the ability to taste natural chemicals similar to PTC helped human ancestors stay away from some toxic things. Substances that resemble PTC today are in some vegetables from the cabbage family (Brassicaceae) such as broccoli, Brussels sprouts, or out Fast Plants!!  Although PTC is not found in nature, the ability to taste it correlates strongly with the ability to taste other bitter substances that do occur naturally, many of which are toxins.

Plants produce a variety of toxic compounds in order to protect themselves from being eaten. The ability to discern bitter tastes evolved as a mechanism to prevent early humans from eating poisonous plants. Humans have about 30 genes that code for bitter taste receptors. Each receptor can interact with several compounds, allowing people to taste a wide variety of bitter substances. Because avoiding bitter plants would severely limit their food sources, strict herbivores have fewer bitter taste genes than omnivores or carnivores. Instead, animals that graze on plants have a high tolerance to toxins. Grazers have large livers that are able to break down toxic compounds.