How To Determine Genetic Makeup Using Family Tree

Pedigree Assay: A Family Tree of Traits

Abstract

Some characteristics, similar the shape of your hairline or whether your earlobes are fastened or detached, are inherited from your parents. In this science project you lot will run into how writing these characteristics onto a family tree can assist y'all determine how they are inherited

Summary

Short (ii-v days)

Basic understanding of genetic principles

Readily available

Very Low (nether $twenty)

No bug

Sandra Slutz, PhD, Science Buddies
Teisha Rowland, PhD, Scientific discipline Buddies

Objective

Use pedigree analysis to determine how several man concrete traits are inherited.

Introduction

Do you have the same hair color or middle color as your mother? Do people say you lot expect just like your grandfather when he was your age? When nosotros look at members of a family it is like shooting fish in a barrel to meet that some physical characteristics or traits are shared, but what are the rules that govern the inheritance of these traits?

It was Gregor Mendel, an Augustinian friar and scientist, who first discovered in the 1860'south that some traits are passed down from generation to generation, in very clear and predictable patterns. Today we know that offspring inherit half of their Deoxyribonucleic acid from each parent. This results in 2 copies of every gene. Many genes come in several different versions, called alleles. Alleles are changes in the actual Deoxyribonucleic acid sequence of the gene. When you lot have 2 identical alleles yous are said to be homozygous for that gene. People with two different alleles are heterozygous for that gene. Whatsoever fix of alleles a person has is called their genotype. The actual trait, such as red, black, or blond hair, which results from a combination of alleles, is referred to as the phenotype.

Mendelian traits— the kind of characteristics Mendel first studied— are due to a single gene. Some of such a gene's alleles are dominant, meaning that if you lot take even one copy of that allele, you will brandish that trait. Mendel took pea plants, which bred true, significant for generation after generation they had the same phenotypes. (Today we know that they bred true because they were homozygous for the traits Mendel was looking at). He took a truthful-breeding majestic flowered constitute and crossed it to a true-breeding white flowered plant and saw that the offspring all had purple flowers. The royal allele was dominant— a single copy of that allele was sufficient. He then took these offspring and crossed them to ane another. This crossing is shown in Figure 1 below, where the height flowers ("Aa") are these heterozygous parents. He plant that their offspring occasionally had white flowers. That is because the white allele was recessive, which means you lot demand 2 copies of that allele to brandish a certain trait. The offspring that inherited the white allele from both parents displayed the white phenotype.

Just like Mendel observed generations of related pea plants to determine the style of inheritance for flower color and other physical traits, scientists can examine generations within a family unit and discover the mode of inheritance for human traits. To do this, scientists create family unit trees, called pedigrees, showing equally many generations of a family as they can and mark who had which phenotype. 2 pedigree examples are shown in Figure two beneath. In lodge for scientists to understand each other'south pedigrees, they use a standard set of symbols and notations. For instance, males are ever designated by a square and females are always designated by a circle.

In this genetics and genomics science projection, you will create pedigrees for 4 human physical traits to determine which phenotypes are ascendant and which are recessive. While information technology has been recently found that these four traits may not exist Mendelian traits (meaning they may be acquired past more one gene, based on more than than two alleles, or afflicted by factors other than genetics), they are still considered to be primarily based on genetics and you lot can investigate them to effort and make up one's mind which are dominant and which are recessive. Here are the four traits you will investigate:

Practise y'all have fastened earlobes or detached earlobes? See Figure 3 below for an example of each.

Some people'due south hairlines come to a V-shaped betoken above their forehead. This is called a widow'south meridian. Encounter Figure 4 below for an case. Exercise you have one or non?

Have a expect at your easily. Do you have lilliputian hairs on your 2d joints, besides called the mid-digits? Some people have hair on their mid-digits, called mid-digit pilus, and some people do not take whatsoever hair in that location, as shown in Figure 5 beneath.

Brand a fist with your thumb sticking upwards. Is your thumb straight or curved? A curved thumb is also known as a hitchhiker's pollex. A slightly curved thumb is shown in Figure half-dozen below.

Terms and Concepts

DNA
Gene
Allele
Homozygous
Heterozygous
Genotype
Phenotype
Mendelian trait
Dominant
Recessive
Mode of inheritance
Pedigree
Attached earlobe
Detached earlobe
Widow'due south peak
Mid-digit hair
Hitchhiker's thumb

Questions

What is a Mendelian trait?
What are the different modes of inheritance for a Mendelian trait?
How do you draw a pedigree?

Bibliography

For a fun and interactive way to acquire about dominant and recessive traits try:

Education Development Eye, Inc. (2002). Weblab: Mendel's Peas. Retrieved February 19, 2008.

Hither you tin can read different discussions on dominant and recessive alleles in humans:

The Tech Museum of Innovation. (n.d.). Dominant vs. Recessive. Stanford at The Tech: Understanding Genetics. Retrieved May fifteen, 2013.

Here is a resources for learning how to create pedigrees:

National Man Genome Inquiry Institute. (n.d.). Your Family Wellness History. National Institutes of Health. Retrieved May fifteen, 2013.

Materials and Equipment

Paper
Pen
Optional: Admission to a photocopier
Lab notebook

Experimental Procedure

Before starting this science project, y'all should go through your reference material and familiarize yourself with the proper mode to draw a human pedigree.

To start this science project, you lot should depict a pedigree showing the different members of your family.
1. Include as many family members every bit you lot can get information from. The more people and generations you include, the more than likely it is that you will take enough information to make up one's mind the mode of inheritance. Ideally you should include multiple people from at least 3 generations (such as you and your siblings, your parents and possibly their siblings, and your grandparents).
2. You might need help from your parents to figure out all the relationships.
If yous have access to a photocopier, brand three copies of the pedigree so that you take four copies total, one for each trait you are going to evaluate. If photocopying is not an pick, manually re-create the pedigree.
Make up one's mind the phenotype of each person on your pedigree for each of the four traits. Employ a split up full-blooded for each trait. Hither are some tips to consider as you fill out the pedigrees:
1. When determining if a person's earlobes are attached or detached, proceed in listen that in that location can be a range of zipper. Practice your best to decide if it looks like the earlobe is fastened or detached. You can write additional observations in your lab notebook.
2. Widow's peaks can vary considerably. When determining if a person has a widow's elevation, count any sort of V-shaped hairline as a widow'southward peak.
  1. You may demand to have a person pull their hair back to look for a widow's meridian.
3. When looking to run across if someone has mid-digit hair, yous may demand to wait closely at their hands. If they have any hair on the mid-digit, fifty-fifty i tiny strand, and then they take mid-digit hair.
  1. If a person does not have mid-digit hair and does a lot of work with their hands, you may want to make a notation of this in your lab notebook because doing a lot of manual hand work may also clothing a person'south mid-digit hair away.
4. When determining if someone has a hitchhiker's thumb, proceed in listen that people'south thumbs come in a wide range of curvedness, from completely straight to very curved. Do your best to make up one's mind if a person'south thumb looks curved or direct. Y'all tin write additional observations in your lab notebook.
From your pedigrees, can you deduce the mode of inheritance for each trait or at to the lowest degree some of the traits? In other words, can you tell if whatsoever of the traits are dominant or recessive? If y'all do not accept plenty information to determine the mode of inheritance of a particular trait, try making a pedigree for another family.

Inquire an Good

Do y'all have specific questions nigh your science projection? Our team of volunteer scientists can assist. Our Experts won't exercise the piece of work for you, but they will brand suggestions, offer guidance, and help you lot troubleshoot.

Variations

Through this science projection, you recorded the phenotypes of various family members for a diversity of traits, and you determined the mode of inheritance for these traits. Now, using this data, predict your ain genotype for these traits. Depending on the genotype of your future mate, what possible phenotypes could your children have?
Through your bibliographic research, did you discover whatsoever other well-known genetic traits in humans? What are they? Do the pedigree analysis for any of those that seem interesting.
Almost characteristics are multigenic, significant that the observed phenotype is due to the activity of several genes in combination. Eye color is an example of a multigenic trait. Do some bibliographic enquiry to learn about how eye color is inherited. Once y'all know how information technology is inherited, draw your family pedigree for centre color. Tin you lot utilise the pedigree and your cognition well-nigh how eye color is inherited to decide the possible genotypes of the family members in your pedigree?
Discovering the mode of inheritance of a trait can sometimes be very hard. For example, people accept long debated whether handedness (i.eastward. beingness left-handed or right-handed) is a genetic trait. The resource below discusses one such scientific theory on handedness. Read this resources and then clarify handedness and hair whorls in your pedigree. Does your information support or refute this theory?
- Brodie, C. (2004). Head in Mitt. Retrieved May fifteen, 2013, from http://www.americanscientist.org/issues/pub/2004/i/head-in-manus

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MLA Style

Scientific discipline Buddies Staff. "Pedigree Analysis: A Family Tree of Traits." Science Buddies, xx November. 2020, https://www.sciencebuddies.org/scientific discipline-fair-projects/project-ideas/Genom_p010/genetics-genomics/full-blooded-analysis-a-family unit-tree-of-traits. Accessed x June 2022.

APA Style

Science Buddies Staff. (2020, November 20). Pedigree Analysis: A Family Tree of Traits. Retrieved from https://www.sciencebuddies.org/scientific discipline-fair-projects/project-ideas/Genom_p010/genetics-genomics/pedigree-analysis-a-family unit-tree-of-traits

Last edit appointment: 2020-11-20

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