Blank raci chart

Pre-lab:

1. Explain what is meant when a gene is referred to as “dominant” or “recessive”:

2. Define genotype:

3. Define phenotype:

Purpose:

1. Understand how genetics relates to the diversity of the human population visible around us.

2. Find out the genotype of a real person.

3. Practice determining the results of genetic crosses.

Background:

Each living thing that reproduces sexually has two sets of chromosomes. One set of chromosomes is inherited from each parent. Each set of chromosomes carries a full set of genes, where each gene is the "code" for a particular type of protein. Having two sets means everyone has two copies of each gene.

Proteins have many roles in an organism and sometimes a single gene is critical in making a certain obvious trait (something observable, like dimples). You can think of each gene as a location and you can put specific information (allele) in each location. The different alleles for a particular gene may produce proteins with identical functions or very different functions. Each type of protein that an organism makes is a product of the alleles that it has. Often the resulting trait is a blend of the effects of the proteins from two alleles, but sometimes one allele (a dominant allele) produces a protein with an effect so powerful that it can completely cover up the effect of a protein produced by a weaker allele (a recessive allele). (2)

Humans are sexually reproducing organism and are different from each other in appearance and in their biochemical make up. Even so, if you compare any two people you will find that 99.9% of their DNA is the same. (3) Human genetic traits are difficult to study because of our relatively long life span and the limited number of human offspring produced. In addition, the number of chromosome pairs (23) increases the possible number of genetic combinations which in turn compounds the difficulty of studying human genetics. In spite of these difficulties humans have some genes that exhibit monohybrid inheritance. For these genes it is possible to get a good idea of your own genotype.

Procedure:

In this exercise you will observe either your own or someone else’s phenotype (part 1) and determine part of your/their genotype (part 2). Then you will figure out one possible genotype of a hypothetical child -a combination of your genes and the genes that are listed for that trait (part 3).

You will Submit the Report Page to Canvas.

Part 1. Determine your phenotype

Read the descriptions of the traits listed below and use a best guess to determine whether you have the dominant or recessive phenotype for each trait. Record the word that describes your phenotype in the spaces provided in the Table on the Report Pages at the end of the lab.

Example:

Trait

Your phenotype

Your possible genotype

Dimples A_

No Dimples aa

No Dimples

Part 2. Deduce your possible genotype(s)

Each of the alleles of a given gene are symbolized by an assigned letter. Normally the dominant form is symbolized by an upper case letter (e.g. E), and the recessive form is symbolized by a lower case of the same letter (e.g. e). If you express the dominant trait (phenotype) use only a single capital letter (e.g. E_ ) for your genotype since you don't know whether you are homozygous or heterozygous for that trait. If you express the recessive phenotype for a given trait you must be homozygous recessive, represented by two lower case letters (e.g. ee). Note: Many of the traits in this lab, while presented as under the control of a single gene, are hypothesized by some scientists to be controlled by several genes. For the purposes of this exercise we will assume the more simple, single gene inheritance.

Part 3. Predict Potential Offspring Phenotypes

The genotype of a potential mate is given in the Report Pages table. Use that information to predict one possible phenotype of an offspring. Record your possible genotypes for each trait in the table on the Report Pages at the end of the lab.

Example (answers are in red):

Trait

Your phenotype

Your possible genotype

Mate’s genotype

One possible phenotype of offspring

A

Dimples A_

No Dimples aa

No dimples

aa

aa

No Dimples

Human Genetic Traits

Dimples (A)

Dimples are small, natural indentations on the cheeks on one or both sides. Some people are born with dimples that disappear when they are adults; others develop dimples later in childhood. Dimples are highly heritable, meaning that people who have dimples tend to have children with dimples—but not always. Because their inheritance is not completely predictable, dimples are considered an “irregular” dominant trait. Having dimples is probably controlled mainly by one gene but also influenced by other genes.

Cleft Chin (B)

A cleft chin looks like a dimple or indentation in the middle of a person’s chin. This trait is due to a single gene with a cleft chin dominant and a smooth chin recessive.

Tongue Rolling (C)

The ability to roll the tongue upward from the sides (so it looks like an "O" or "U" from the front) is a dominant trait. It is probably the result of several genes with an environmental influence, though in genetics labs it is usually treated as a one-gene trait. It probably means that tongue rollers have more flexible muscle or connective tissue associated with the tongue. With the non-roller recessive trait (cc) a person only produce a slight downward curve of the tongue.

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Widow's Peak (D)

The widow's peak is a distinct downward point on the hairline at the top center of the forehead. This is a dominant trait. If you have a straight hairline, you have recessive alleles for this trait.