Select your language

Suggested languages for you:
Log In Start studying!
StudySmarter - The all-in-one study app.
4.8 • +11k Ratings
More than 3 Million Downloads
Free
|
|

All-in-one learning app

  • Flashcards
  • NotesNotes
  • ExplanationsExplanations
  • Study Planner
  • Textbook solutions
Start studying

Pedigree Analysis

Save Save
Print Print
Edit Edit
Sign up to use all features for free. Sign up now
Biology

Pedigrees are some of the most fun and exciting tools we have in inheritance studies. Learning how to analyze them requires pattern recognition and deductive reasoning, but these learning processes are not complicated since they are visual. By using common sense and some fundamental principles, we can analyze pedigrees for just about any trait - from black hair color to osteogenesis imperfecta to dimples.

Definition of Pedigree Analysis in Biology

Pedigree analysis is an analysis, examination, or demonstration of the inheritance pattern of particular trait(s) in human beings.

In the context of genetics, medicine, and biology, these traits are typically diseases and disorders. Think of pedigrees as a family tree, but instead of perhaps going into detail about ethnic backgrounds or country of origin, pedigrees describe who has, who doesn't have, and who carries a genetic disorder (or multiple disorders!).

Pedigree analysis is visualized with a chart or diagram that maps out all relevant members of a family and exactly how they are related to one another. Most pedigrees have a basic level of detail - they demonstrate who's married to who, who is deceased, and the number of progeny and their sex.

Some pedigrees are more detailed, perhaps demonstrating the cause of death for those deceased, or adopted vs biological children.

Regardless of their level of detail, pedigrees highlight who is affected by the disorder in question and who is not. Those affected are typically marked in black, while those unaffected (considered the normal phenotype) have no coloring (or white). The typical denotations in the pedigree analysis are seen below (Fig. 1).

pedigree analysis typical pedigree symbols khan academy, StudySmarterFigure 1: Typical pedigree symbols. Khan Academy.

Pedigrees easily demonstrate the phenotypes of the individuals being studied. We can then use them to determine the genotypes of existing family members. We can even use them to predict the genotype and phenotype of future offspring, like in a married couple who wants to know the odds of one of their children having a particular disease.

Pedigree Analysis Examples

We know the basic structures of pedigrees, the meaning of their symbols, and that they are used in genetics to study inheritance patterns. But what are the possible inheritance patterns we can see using pedigrees? And which traits have which kind of particular inheritance pattern? We will determine the answers to these questions with examples of each pedigree, of which there are six in Mendelian genetics.

1. Autosomal Recessive Trait - a Pedigree Analysis of Galactosemia

The first and most common inheritance pattern that can be analyzed by pedigree is that of the autosomal recessive trait. What kind of genes have an autosomal recessive pattern? Thankfully, most genetic diseases! Why thankfully? Well, because an autosomal recessive trait must have two alleles in order for it to appear in the phenotype of an individual, thus the chances of suffering from a recessive trait are lower than those of suffering from a dominant trait. This creates three classes of individuals when it comes to an autosomal recessive pattern of inheritance: those who have the disease (homozygous recessive), those who are carriers (heterozygous), and those who are neither (homozygous dominant).

Let's use the disease galactosemia to study this.

Galactosemia is a disorder of galactose accumulation in the blood due to a defect in the enzyme that metabolizes it.

This build-up of galactose can be toxic to certain tissues of the body. Galactose is present in lactose, which is present in milk, so the first symptoms of galactosemia usually appear in the first couple days of life, after the new baby drinks formula or breast milk. These symptoms include vomiting, diarrhea, being really weak, and even cataracts due to excess galactose in the eyes.

Galactosemia: galacto - referring to galactose, a sugar, semia - in the blood.

Galactosemia is an autosomal recessive disorder. Both mom and dad need at least one copy of this disorder for one of their children to have it. Let's look at a pedigree with such a scenario (Fig. 2).

Pedigree analysis, galactosemia pedigree texas dept of state, StudySmarterFigure 2: Galactosemia pedigree. Texas Dept of State.

This is a simple pedigree, but we can see that this heterozygous couple (genotypes Gg) had one child with galactosemia, and three children with the normal phenotype. Because this is an autosomal recessive trait, carriers will not have the disease or any symptoms.

What if we were look at a pedigree analysis of galactosemia (or any other autosomal recessive trait), but it was not labelled as such? What tricks would we use to classify the trait being studied in the pedigree as autosomal recessive? Let's look at an unlabeled example to assess this (Fig. 3).

Pedigree analysis, autosomal recessive pedigree google sites, StudySmarterFigure 3: Autosomal recessive pedigree. Google Sites.

Looking at the youngest generation (generations are often labelled, with the oldest generation being I, their descendants being II, and the youngest being III), we can see there is a male child who is affected by galactosemia. We can see that neither his sisters nor his parents have galactosemia. Thus, we can rule out:

  • autosomal dominant (at least one parent would have to have the disorder to pass it down),
  • Y-linked (the father must pass this down, so he would have the disorder)
  • mitochondrial (a mother passes this down to all her children), and
  • X-linked dominant (the mother would have to have this disorder to pass it down to her son). However, we cannot rule out X-linked recessive.

Let us look further up this pedigree, at the first generation. We see there is another person affected with this trait in this family, in Generation-I. This affected woman gave birth to two sons, and two daughters. None of those children are affected (draw this pedigree yourself to get some practice!).

Let us consider the scenario in which the trait this woman has is X-linked recessive. She would have to have two copies of this allele to have the disease, because women have two X-chromosomes. So she would only have the disordered allele to give to her children, and while her daughters would get a normal X-chromosome from their father, all her sons would get an affected X-chromosome from her and a normal Y-chromosome from their father, and thus would have to be affected as well. That is not the inheritance pattern we see here, and this rules out the possibility that this trait, in this case galactosemia, is inherited in an X-linked recessive pattern.

Now, if this affected woman in Generation-I has an autosomal recessive trait, then her genotype must include two copies of the affected allele (gg) and she would once again be able to distribute only this to her offspring, However, if their father has a homozygous healthy genotype, GG (which is typically assumed), then all their progeny would have the Gg heterozygous genotype. All four of their children in Generation-II would be carriers. This explains how the woman in Generation-II, who married a random man who perhaps was a carrier as well, gave rise to an affected offspring.

2. Autosomal Dominant - How We Can Use Pedigree Analysis to Find Genetic Disorders With This Inheritance Pattern

Generally, autosomal dominant disorders are present in every generation. This is in contrast to autosomal recessive disorders that are said to "skip generations". Autosomal dominant traits are one of the easiest to recognize on pedigrees because every person exhibiting the trait has at least one parent exhibiting the trait. (Fig. 4)

Pedigree analysis, autosomal dominanat pedigree, StudySmarterFigure 4: Autosomal Dominant pedigree. Chegg.

Let's say this is a pedigree of a family with Huntington's, a disease that causes problems with movement, neurological and psychiatric problems, often resulting in premature death. How can we know that this disease is inherited in an autosomal dominant fashion? We see in Generation-I an affected man passes it on to three of his children- two daughters and one son. Each affected person in Generation-II passes the disorder on to at least one of their children, and the Generation-II son who did not inherit the disorder, and did get married, did not pass it on to any of his four children. Thus, that son is homozygous for the normal allele, and the affected individuals are all heterozygous for this trait.

3. X-linked Recessive

X-linked recessive disorders are passed from a woman (who is typically a heterozygote carrier) to both her sons and daughters. However, all her sons will have the trait of the disorder, and her daughters (assuming her husband has the normal genotype) will either be carriers or homozygous for the normal allele (Fig. 5). If a man happens to have an X-linked recessive disorder, he cannot pass it down to his sons, whom he must pass his Y chromosome down to. Therefore all his sons will be unaffected, but his daughters may be carriers.

Pedigree analysis, X-linked recessive pedigree Chegg, StudySmarterFigure 5: X-linked recessive pedigree. Chegg.

The above pedigree may seem very complex, but we can break it down to understand some basic principles. Firstly, all affected individuals are males and they are inheriting this disorder from parents, both of which are not affected. If this disorder had an autosomal recessive inheritance, it would be seen in both male and female descendants. Because it is exclusively seen in males, we can safely presume the disorder is X-linked recessive.

4. X-linked Dominant

Most X-linked disorders are recessive, but a few are dominant. This means that the parent who has the trait also has the disorder, and when they pass this trait down the children who receive it will be affected as well (Fig. 6).

Pedigree analysis, x-linked dominant pedigree michigan genetics, StudySmarterFigure 6: X-linked dominant pedigree. Michigan Genetics.

A woman with an X-linked dominant disorder passes it down to her sons and daughters equally. One of the biggest hints suggesting X-linked dominant disorders is that a man who has an X-linked dominant disorder must pass it down to all his daughters, as that is the only chromosome he can give them.

5. Y-linked Disorders

Very few disorders or traits have been discovered to be Y-linked. In fact, the preponderance of disorders that primarily affect men is typically due to the presence of a single X-chromosome, such that whatever disordered trait is on that chromosome cannot be masked by the normal trait that would be on a paired X-chromosome in females.

Pedigree analysis, y-linked pedigree wiki, StudySmarterFigure 7: Y-linked pedigree. Wiki.

Ultimately, we can know Y-linked traits because they never occur in females, only in males (Fig. 7). And an affected male must pass the trait down to all his sons. Some forms of deafness are Y-linked.

6. Mitochondrial Inheritance

Mitochondrial inheritance is maternal, meaning we get our mitochondria from our mothers. Thus, an affected woman passes down a trait to all her children, and only her daughters can pass it on to their children (Fig. 8).

Pedigree analysis, mitochondrial inheritance ncbi, StudySmarterFigure 8: Mitochondrial inheritance pedigree. NCBI.

Human Pedigree Analysis: Problem Sheet

Now that we know the six major groupings of pedigree analysis, we can develop a problem sheet - in the form of a table- to help us consolidate the principles of each pedigree (Table 1).

Inheritance PatternTips
Autosomal recessive
  • may see unaffected parents have affected offspring
  • both unaffected parents with affected offspring must be heterozygotes
  • these traits tend to skip a generation or two
Autosomal dominant
  • unaffected parents cannot have affected offspring
  • any affected parents (almost always) are heterozygotes
  • these traits are present in every generation
X-linked recessive
  • typically only sons are affected
  • any affected daughter must have an affected father
X- linked dominant
  • if passed down by mother: males and females equally affected
  • if passed down by father: only females affected
Y- linked
  • only occurs in male progeny
  • passed down by father
  • occurs in all male progeny of an affected father
Mitochondrial inheritance
  • passed down exclusively by mother
  • occurs in all children of an affected mother, regardless of gender
  • affected sons cannot pass this down to their children

Table 1: Hints for pedigree analysis problem sheets. Chisom, Studysmarter.

Pedigree Analysis - Key takeaways

  • Pedigrees can help us to analyze the inheritance patterns of many traits
  • Pedigrees are typically used in the setting of genetic disorders
  • The most common inheritance patterns include autosomal recessive, autosomal dominant and X-linked recessive.
  • Some other less common inheritance patterns include X-linked dominant, Y-linked and mitochondrial inheritance.
  • To solve a pedigree analysis, first look for dominance, than look for possible sex-linkage.

Pedigree Analysis

To solve a pedigree analysis, we must first determine if the trait is dominant or recessive. Look at parents and children's state to determine this. 

Pedigree analysis is important because it helps us to predict the likelihood of future offspring having a disorder.

A pedigree analysis is a visual depiction of the genetic states of members of a family - carriers, affected, or completely unaffected.

Analyze a pedigree by first determining the dominance of a trait, and then determining its sex-linkage.

Final Pedigree Analysis Quiz

Question

What kind of inheritance pattern does sickle cell anemia have?

Show answer

Answer

autosomal recessive

Show question

Question

Which of these inheritance patterns is the rarest for genetic disorders?

Show answer

Answer

y-linked

Show question

Question

What is the name of the disorder that causes severe respiratory illnesses, is very common in North European individuals, and is due to a defect in chloride channels?

Show answer

Answer

Cystic Fibrosis

Show question

Question

What two tools are used frequently to test for the presence of trisomy in a fetus while they're still in utero?

Show answer

Answer

Chorionic Villus Sampling and Amniocentesis

Show question

Question

What is the name of the tool/method that allows us to visualize chromosomes to examine their size, number, and shape?

Show answer

Answer

Karyotyping

Show question

Question

What is the inheritance pattern of Hemophilia?

Show answer

Answer

x-linked recessive

Show question

Question

What kind of inheritance pattern leads to a mother passing down her disorder to all her children, boys and girls?

Show answer

Answer

Mitochondrial inheritance

Show question

Question

Rett Syndrome is an X-linked dominant disorder. How many mutated chromosomes does a girl need to have this disorder?

Show answer

Answer

One

Show question

Question

What is a trisomy?

Show answer

Answer

A chromosomal disorder where there are three copies of a chromosome instead of two.

Show question

Question

If a father has a disease and passes it down to all his daughters, but none of his sons, what is the inheritance pattern of this disease?

Show answer

Answer

X-linked dominant.

Show question

Question

How many copies of the hemophilia mutation do girls need to have the disorder?

Show answer

Answer

Two copies

Show question

Question

What tool can be used to look at the incidence of a disease in a family over several generations?

Show answer

Answer

A pedigree.

Show question

Question

True or False: X-linked recessive disorders are much more common in boys.

Show answer

Answer

True

Show question

Question

What ethnic background has a higher incidence of sickle cell anemia?

Show answer

Answer

West Africans

Show question

Question

What ethnic background has a higher incidence of Tay Sachs Disease?

Show answer

Answer

Ashkenazi Jewish people

Show question

Question

What type of inheritance pattern could show a pedigree where a mother passes down a trait to all her children, sons and daughters?

Show answer

Answer

Mitochondrial inheritance

Show question

Question

True or False: A man passes down an X-linked dominant trait to all his daughters

Show answer

Answer

True

Show question

Question

True or False: A man passes down an X-linked dominant trait to all his sons. 

Show answer

Answer

False

Show question

Question

If a woman has an autosomal recessive allele, and her husband has the same allele, but both of them have the normal phenotype, what is the probability that one of their offspring has the recessive phenotype?

Show answer

Answer

25%

Show question

Question

Fill in the blank: Autosomal recessive disorders typically _____ a generation

Show answer

Answer

Skip

Show question

Question

Fill in the blank: Autosomal dominant disorders are typically present in _____ generation

Show answer

Answer

All

Show question

Question

Galactosemia can be passed down from mother to sons, or mother to daughters, or father to sons, or father to daughters. Two copies of the galactosemia allele are required to have the disease. What is the inheritance pattern for this disease?

Show answer

Answer

Autosomal recessive

Show question

Question

People who have autosomal dominant disorders are typically __________

Show answer

Answer

Heterozygotes

Show question

Question

Most genetic disorders are inherited in which pattern?

Show answer

Answer

Autosomal recessive

Show question

Question

Which is most common; X-linked dominant disorders, X-linked recessive, or Y-linked?

Show answer

Answer

X-linked recessive

Show question

Question

Why can't a male with a mitochondrially inherited disorder pass it down to his offspring?`

Show answer

Answer

Because mitochondria are maternally inherited. His offspring will get their mitochondria from their mother.

Show question

60%

of the users don't pass the Pedigree Analysis quiz! Will you pass the quiz?

Start Quiz

Discover the right content for your subjects

No need to cheat if you have everything you need to succeed! Packed into one app!

Study Plan

Be perfectly prepared on time with an individual plan.

Quizzes

Test your knowledge with gamified quizzes.

Flashcards

Create and find flashcards in record time.

Notes

Create beautiful notes faster than ever before.

Study Sets

Have all your study materials in one place.

Documents

Upload unlimited documents and save them online.

Study Analytics

Identify your study strength and weaknesses.

Weekly Goals

Set individual study goals and earn points reaching them.

Smart Reminders

Stop procrastinating with our study reminders.

Rewards

Earn points, unlock badges and level up while studying.

Magic Marker

Create flashcards in notes completely automatically.

Smart Formatting

Create the most beautiful study materials using our templates.

Sign up to highlight and take notes. It’s 100% free.