Family studies on genetic inheritance

Introduction: (Initial Observation)

Genetic studies can be performed to identify the effect of gene on properties and characteristic of any organism. (Gene is a hereditary unit that occupies a specific location on a chromosome and determines a particular characteristic in an organism.) We may perform genetic studies on human, animals, plants and even bacteria. Every genetic study will focus on a different characteristic of the subject. Genetic studies on hair color and facial features such as eye color and shape of ears are among genetic studies that can be performed on humans and can be conducted by Intermediate or senior students.

The general purpose of doing these experiments is to understand the effect of gene on certain characteristics of humans and compare it with other environmental factors that may have a similar effect.
Authors note: The first time that I learned about world countries and the fact that African people are black and people from the north pole are white, I wondered if it can be the effect of weather and temperature. I though Africans are black because of sun-burn and people from north pole are white because of the fat layer under their skin caused by a cold weather. Later when I learned that African people will remain black even if they move to a colder area, again I thought maybe millions of years exposure to the hot sun at African deserts has had a long lasting effect on their skin and if they live in a cold area for the same amount of time, they may change color and become white again. Today genetic studies can help us to understand the effect of gene on skin color and on many other characteristics of human.

Information Gathering:

While you do research about genetic (hereditary) characteristic, it is good idea to look at a few other similar studies. Here are some:

http://vector.cshl.org/dnaftb/5/concept/fs.html

http://www.budgerigars.co.uk/genetics/pilk.html

Information that you gather, will give you some idea, but finally you have to do the job and do your own research.

Question/ Purpose:

What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement.

What characteristics do people inherit from their parents?

By looking around we notice that people have different eye colors, different hair colors, different shapes of ears and fingers and toes. Even amount and distribution of body hair varies among people. For the purpose of this project we want to discover which of the above characteristics is inherited from parents or other ancestors.

Identify Variables:

When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.

We may inherit special characteristics from our biological parents or from our ancestors. In this specific study we will try to identify the special characteristics that we may inherit from our ancestors.

Independent variable (also known as manipulated variable ) is human race. Possible values are individuals who you randomly select from different races, nationalities or ethnic groups for your study. This may also be called a collection.

Dependent variable can be any characteristic that we are studying such as eye color finger length, and shape of ears. Many of such dependent variables can be studied at the same time. Every human characteristic such as size, shape and color of body parts or even habits and some behaviors can be a variable in our study. List variables that you select for your study in this section. To find out if certain characteristic is hereditary, you need to gather information about presence of such characteristic and racial information on a large number of individuals.

As you will see later in experiment section, we have selected more than one dependent variable for our study.

Hypothesis:

Based on your gathered information, make an educated guess about the characteristic that are hereditary. Identifying variables is necessary before you can make a hypothesis.

Sample hypothesis:

Hair color and facial features such as eye color and shape of ears can have a genetic root and that is why often we can identify the race of people by a quick look (Unless they have a mixed genetic background).

Experiment Design:

Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”

Procedure:

Design a questionnaire for the information that is subject of your study and distribute it among classmates and family friends. Then compile the results in tables and analyze it to reach to a conclusion. This is a sample questionnaire (Modify it as you like):

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Materials and Equipment:

Paper, pen, computer and a spreadsheet program such as MS EXCEL.

Results of Experiment (Observation):

A collection of completed questionnaires will serve as the result of your experiments.

Enter the results in a table in a way that one row will be used for each participant and each column represents one answer. Use letters for answers. For example A for first choice, B for second choice, …. So, for question number 3, A means male and B means female.

Following is a sample table. Your actual results table will have more columns and more rows.

Using the data in the above table, you can compile a series of other tables that show the percentage of each attribute in each ethnic background. In such tables the independent variable (race or ethnic background) may be in rows and the rate of people in each attribute (dependent variable) will be in columns.

You will need a separate table for each attribute. To do that enter the data in a spreadsheet program (like Excel) and then sort the table based on different columns to help you analyze the results. Find out what percentage of each race have certain characteristic.

Following is a sample table for Eye color.

Rate of certain eye colors in different ethnic groups.

See the calculation section to find out how the 20%  in the above table is calculated.

For each characteristic you will have one results table that shows the ratio of that characteristic in a specific ethnic background. Use these ratios to draw a conclusion. Your conclusion may indicate which characteristics are hereditary.

Calculations:

You need to calculate the rate of population in each race with certain characteristic. To do that you divide the number of matching subjects for a certain characteristic by the total number of subjects for each race.

For example after sorting the first results table based on ethnic background, all “A”s will be next to each other and you can easily count them. So if 15 of your subjects are white, you will have 15 “A”s in the ethnic background column next to each other. Count the number of Brown eyes where the ethnic background is “A”. Divide that by 15 (total number of whites) to find out the rate of brown eyes in white people. If you have 3 brown eyes, then 3/15=0.20. So 20% of white people have brown eyes.

You must repeat such calculation for each characteristic of each ethnic group.

Summary of Results:

Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.

It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.

Conclusion:

Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.

Related Questions & Answers:

What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.

Possible Errors:

If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.

If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.

References:

List of References