Name: reading family traits in pedigrees
Uploaded: 2026-08-26T08:20:46.165Z
Duration: 2 min 21 s
Channel: JoVE

K12 Standards

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NC K-12 Science Standard Course of Study

9-12

Biology

heredity-inheritance-and-variation-of-traits

Heredity- Inheritance and Variation of Traits

LS.Bio.7.2

Pedigree Analysis

One way scientists study the inheritance of traits and genetic disorders in humans is through the analysis of family trees, also known as pedigrees.In a typical pedigree, squares represent males, circles represent females, and a horizontal line between these shapes represents a mating.If such a union produces children, a vertical line is drawn downward from the parents toward the sons and daughters.Progressively lower rows in the pedigree represent successive generations in a family.Shaded symbols represent individuals affected by the trait or disorder. Half-shaded symbols represent carriers of a recessive disorder who are typically unaffected but can pass the mutation to offspring. A diagonal slash through a symbol indicates that the individual is deceased.For example, in a pedigree for biotinidase deficiency, shaded symbols represent individuals diagnosed with the disorder, including those showing symptoms such as skin rashes.Biotinidase deficiency results from absent or reduced biotinidase enzyme activity, which is responsible for recycling biotin or vitamin B7.By assessing which family members have been diagnosed with biotinidase deficiency, researchers can determine whether this disease results from a recessive or dominant mutation in a single gene located on an autosome or a sex chromosome.Here, males and females are affected at similar rates.Unaffected parents can have children with the disorder, and not every generation contains a family member with the disease. This pattern suggests that biotinidase deficiency is autosomal recessive.Importantly, pedigree analysis not only shows inheritance patterns but can also help couples understand their risk of having a child with the disorder, based on their family history.

pedigree analysis

A pedigree is a diagram displaying a family&#x2019;s history of a trait. Analyzing pedigrees can reveal (1) whether a trait is dominant or recessive, (2) the type of chromosome, autosomal or sex, a trait is linked to, (3) genotypes of family members, and (4) probabilities of phenotypes in future generations. For families with a history of autosomal or sex-linked diseases, this information can be crucial to family planning.<h4>Pedigrees Display Family Histories</h4>In various plant and animal species, scientists study the inheritance of phenotypes, or traits, using carefully controlled mating experiments called crosses. For example, monohybrid crosses can establish trait dominance or recessiveness, and test crosses can determine the genotype (homozygous or heterozygous) of an organism exhibiting a known dominant phenotype.Humans, however, cannot be ethically or feasibly crossed. Therefore, researchers analyze pedigrees, or family trees, to understand how human traits and diseases are inherited. Pedigrees display a family&#x2019;s history of a trait across generations and family members. Using the same principles that apply to crosses to analyze reproductive events that have already occurred, information about trait heritability can be inferred.<h4>Rows of a Pedigree Represent Generations of a Family</h4>On a typical pedigree, squares represent males and circles represent females. Shaded squares or circles signify the presence of a trait of interest. Rows are generations, sometimes labeled with Roman numerals. The oldest generation comprises the top row, with each subsequent generation on separate rows. Within each generation, or row, family members may be labeled numerically from left to right and referred to by their generation and position. For instance, the second individual in the first generation is I-2.A horizontal line connecting two parents is called a marriage line, although marriage is not necessarily involved. A vertical line of descent extending downward from a marriage line connects to a horizontal sibling line. Individuals connected to the line of descent via the sibling line are offspring. Individuals that are not directly connected to the sibling line entered the family via marriage lines, and are not biological offspring of the preceding generation.<h4>Pedigrees Reveal Information about Trait and Disease Inheritance</h4>Dominant traits are distributed differently than recessive traits. Inheritance is also distinct for traits determined by genes on sex chromosomes compared to traits linked to autosomes (non-sex chromosomes). By examining a trait&#x2019;s presence and absence throughout a family&#x2019;s history, pedigree analysis can provide information about trait inheritance. Although many diseases are influenced by multiple genes, several display Mendelian inheritance patterns. For these conditions, pedigrees can give important clues about the risk of disease inheritance and propagation.Traits caused by genes on autosomes and requiring two allele copies to influence a phenotype are autosomal recessive. Several disorders are autosomal recessive, including cystic fibrosis, Tay-Sachs disease, and maple syrup urine disease. Most people with these diseases have heterozygous parents who do not have the condition but carry a causal allele.These carriers can unknowingly impart the disease to their children, which partially explains why autosomal recessive diseases are more common than their dominant counterparts. Comparing generations on a pedigree can reveal whether an autosomal trait is dominant or recessive. Neither parent has the trait, but one child inherits it. Thus, it must be recessive.Freckles and polydactylism (extra fingers or toes) are autosomal dominant traits in humans, requiring only one copy of the determining allele to influence phenotype. Autosomal dominant diseases, such as Huntington&#x2019;s disease, afflict ~50% of offspring with one affected parent. Many of these diseases do not cause symptoms until later in life, after reproductive age. Children can inherit these diseases from unknowingly affected parents, highlighting the importance of analyzing family history. Although both parents exhibit the trait, one of their children does not. Since a cross between two recessive parents consistently produces a recessive phenotype, this trait must be dominant.<h4>Traits Can Be Autosomal or Sex-linked</h4>In addition to 44 autosomes, humans have two sex chromosomes, which are homologous in females (XX), but non-homologous in males (XY). Traits determined by sex chromosomes are sex-linked. Most sex-linked traits in humans are X-linked recessive. Only males can inherit Y-linked traits because females lack a Y chromosome. Additionally, the X chromosome contains ~800-900 protein-coding genes compared to ~70-80 on the Y chromosome.X-linked traits include hemophilia, muscular dystrophy, and red-green color blindness. Since males have only one X chromosome, they are hemizygous (rather than homozygous or heterozygous) for an X-linked trait. Males are more susceptible to recessive X-linked traits than females because they have no second allele to potentially mask a causal recessive allele.

Overview

A pedigree is a diagram displaying a family&#x2019;s history of a trait. Analyzing pedigrees can reveal (1) whether a trait is dominant or ...

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Education

JoVE Core

Genetics

Classical and Modern Genetics

KEY TERMS AND CONCEPTS

reading family traits in pedigrees

Pedigrees are family trees used to track how a trait passes through generations. They help scientists and students see whether a trait is dominant or recessive, whether it is autosomal or sex-linked, what genotypes family members may have, and what phenotypes may appear in future generations. For families with a history of inherited disease, this information can be important for family planning.

In plants and animals, inheritance is often studied with crosses. Monohybrid crosses can show whether a trait is dominant or recessive, and test crosses can help identify whether an organism with a dominant trait is homozygous or heterozygous. Humans cannot be crossed for ethical or practical reasons, so pedigrees are used instead. A pedigree records reproductive events that have already happened and lets scientists infer how a trait is inherited.

Pedigree symbols follow a clear pattern. Squares stand for males, and circles stand for females. Shaded symbols show the trait of interest. The top row is the oldest generation, and each lower row is a later generation. Family members in a generation may also be numbered from left to right, such as I-2. A line between two adults marks a parent pair, and a line downward connects them to their children through a sibling line.

Looking across generations can reveal inheritance patterns. If neither parent shows a trait but one child does, the trait is likely recessive. Traits caused by genes on autosomes and needing two allele copies are called autosomal recessive. Examples include cystic fibrosis, Tay-Sachs disease, and maple syrup urine disease. In many cases, the parents are heterozygous carriers who do not show the condition but can pass the allele to their children.

A pedigree can also point to dominant traits. Freckles and polydactylism, or extra fingers or toes, are autosomal dominant traits. Only one copy of the allele is needed to affect phenotype. Huntington’s disease is another autosomal dominant example, and about 50% of offspring may be affected when one parent has the trait. Some dominant diseases do not show symptoms until later in life, which is why family history can matter even when parents seem healthy. If both parents show the trait but one child does not, the trait is likely dominant because two recessive parents would produce only the recessive phenotype.

Pedigrees also help identify sex-linked traits. Humans have 44 autosomes and two sex chromosomes. Females are XX, and males are XY, so the sex chromosomes are homologous in females but not in males. Traits on sex chromosomes are sex-linked. Most sex-linked traits in humans are X-linked recessive. Examples include hemophilia, muscular dystrophy, and red-green color blindness. Males have only one X chromosome, so they are hemizygous for X-linked traits and are more likely to show a recessive X-linked allele because there is no second copy to mask it. Y-linked traits can be inherited only by males, since females do not have a Y chromosome.

Reading Family Traits in Pedigrees

genetic lingo

Genotype, Phenotype, and Inheritance

Genotype, phenotype, and inheritance help explain how traits and disease risk are passed from parents to offspring. In diploid organisms, including humans, most other animals, and many plants, somatic cells carry a duplicate set of chromosomes. These chromosome pairs are homologous, with similar length, centromere position, and gene locations. Diploid organisms inherit two versions of each gene, one from each parent. These versions are called alleles, and they sit at the same relative locus,...

punnett squares

Punnett Squares for Predicting Traits

Punnett squares help predict which traits offspring may inherit from two parents. They show possible genotypes, which are pairs of alleles, and can also show the chance of a phenotype, or visible trait, when the inheritance pattern is known. These grids work best for traits controlled by a single gene locus and passed on independently during meiosis. Punnett squares were developed in the early 1900s by Reginald Punnett. His work came after Gregor Mendel’s pea plant experiments revealed the...

monohybrid crosses

Mendel’s Pea Plant Inheritance Ratios

Gregor Mendel used pea plants to study how traits are passed from parents to offspring. His breeding experiments in the 1850s and 1860s showed that inheritance follows clear patterns. He crossed true-breeding plants that differed in one trait and found that dominant traits can hide recessive traits. Mendel focused on seven pea plant traits, and each trait had two forms controlled by a single gene locus. He noticed that true-breeding plants always produced offspring with the same phenotype, or...

dihybrid crosses

Mendel's Law of Independent Assortment

Mendel’s law of independent assortment explains how two traits can be inherited separately. Gregor Mendel tested this idea with pea plants that differed in two characteristics, such as pea color and pea shape. He used true-breeding parents that were homozygous for both traits but showed different phenotypes. In one example, Mendel crossed round, yellow peas with wrinkled, green peas. The parental generation had RRYY and rryy genotypes. Their first-generation offspring were all dihybrids,...

law of segregation

Mendel’s Pea Cross Ratios

Mendel’s pea plant crosses show how traits can disappear in one generation and return in the next. When he crossed plants, one parental trait sometimes seemed to vanish in the F1 generation and reappear in the F2 generation. Mendel used this pattern to explain why some traits are dominant and others are recessive. He proposed that traits are controlled by alleles, which are different versions of a gene. An organism inherits two copies of each gene, one from each parent. In his model, a...

law of independent assortment

Mendel’s Dihybrid Cross and Trait Ratios

Mendel’s dihybrid cross shows how two traits are inherited at the same time. A dihybrid cross is a cross in which both parents are homozygous for two distinct traits, and the F1 generation is heterozygous for both traits. Mendel used pea plants with round yellow peas and wrinkled green peas as an example. One parent had genotype YYRR, and the other had genotype yyrr. In the F1 generation, every plant showed the dominant traits, so the plants were YyRr and had yellow, round peas. The F2...

test cross

Using Test Crosses to Identify Genotypes

Test crosses are used to identify the genotype of an organism with a dominant trait. A genotype is the pair of alleles inherited for a gene, and alleles are different forms of the same gene. In diploid organisms, including humans, each gene usually has two alleles, one from each parent. An allele is recessive when its effect is hidden by another allele at the same gene location. Pea plants provide a clear example with flower color. White flowers are recessive, because one copy of the purple...

probability laws

Inheritance Risk with Sum and Product Rules

Inheritance risk can be calculated with the sum rule and the product rule. The sum rule applies to mutually exclusive events, or events that cannot happen at the same time. The product rule applies to independent events, or events that do not affect one another. These rules describe theoretical probability, which is the chance of an event before it happens. Empirical probability is different because it is based on events that have already occurred. These probability rules are useful in...

Pedigrees are family trees used to track how a trait passes through generations. They help scientists and students see whether a trait is dominant or recessive, whether it is autosomal or sex-linked, what genotypes family members may have, and what phenotypes may appear in future generations. For families with a history of inherited disease, this information can be important for family planning. In plants and animals, inheritance is often studied with crosses. Monohybrid crosses can show...

multiple allele traits

Blood Type and Allele Interactions

Multiple alleles can shape traits through blood type, sickle cell anemia, incomplete dominance, and codominance. Multiple allelism means a gene has three or more allelic forms. Diploid organisms, including humans, usually carry only two alleles for each gene, but many human genes exist in multiple forms in the population. Human blood type is a clear example of multiple allelism. The blood type gene has three alleles: I A , I B , and i. These alleles help determine which blood type a person has...

epistasis

Gene Masking in Rabbit Fur Color

Epistasis describes how one gene can mask or change the effect of another gene. In high school genetics, this helps explain why many traits do not follow a simple single-gene pattern. Instead, alleles at different locations can work together to shape the final phenotype. Mendel studied seven unrelated pea traits, but most traits involve multiple gene interactions. Epistasis often happens when one gene interferes with the expression of another gene. It can also occur when genes are part of the...

polygenic traits

Polygenic Traits in Human Height

Polygenic traits are traits controlled by more than one gene. Human height is a clear example of this kind of inheritance. Because many genes work together, the final trait can vary a lot from person to person. Researchers have found hundreds of loci, or gene locations, that influence height. There are likely many more that have not yet been identified. Many of these genes affect cartilage in the growth plates of the long bones in the arms and legs, either directly or indirectly. Height is...

pleiotropy

SOX10 and Multiple Traits in Pleiotropy

Pleiotropy is when one gene affects more than one trait. The SOX10 gene is a clear example because it can influence pigmentation, hearing, and intestinal movement. These traits may seem unrelated, but they can all be linked to the same gene change. In humans, a deleted region in SOX10 can cause Waardenburg Syndrome Type 4, or WS4. WS4 is an autosomal recessive disorder, which means a person usually inherits two altered copies of the gene. Common signs include a white forelock,...

nature and nurture

Genes and Environment Shape Height

Genes and environment both shape human height and other traits. Genes are the inherited instructions we get from our parents. Environment includes factors such as diet, stress, and social conditions. Many phenotypes, or observable traits, reflect both influences. Some also show up later in life, including cancer and other diseases. Height is a clear example of this interaction. Scientists estimate that 70-90% of height variation comes from genetic differences among people. The remaining 10-30%...

chromosomal theory of inheritance

How Genes Map to Chromosomes

Genes map to chromosomes, and this idea explains how Mendel’s inheritance patterns work. Gregor Mendel published his pea plant breeding results in 1866. He showed that physical traits follow predictable patterns. At the time, scientists did not yet know that genes existed. Mendel used the word "factors" for the hereditary units he studied. The details behind Mendel’s laws of segregation and independent assortment were still unknown for many years. In the late 1800s, better microscopes and...

non-nuclear inheritance

Maternal DNA in Mitochondria and Chloroplasts

Maternal DNA in mitochondria and chloroplasts explains how some genes are inherited outside the nucleus. Most DNA is in the nucleus, but mitochondria and chloroplasts in the cell cytoplasm also carry their own DNA and can copy it independently of nuclear DNA. Mitochondria are found in both plant and animal cells. They are called the powerhouses of eukaryotic cells because they break down glucose to make energy for cellular activity. Mitochondrial DNA has about 37 genes, and many help with...

x-linked traits

X-Linked Inheritance in Families

X-linked inheritance explains how traits on the X chromosome are passed through families. In most mammalian species, females have two X sex chromosomes, while males have one X and one Y. A mutation on one X chromosome may be masked in females by a normal allele on the other X. In males, that same mutation is more likely to show because there is no second normal X to balance it. Traits caused by changes on the X chromosome are called X-linked traits. Color blindness is a well-studied example.

sex-linked disorders

X- and Y-Linked Disorder Patterns

X- and Y-linked disorders come from mutations in genes on the sex chromosomes. These genes, like those on autosomes, are needed for normal body function. When a mutation causes a biological problem, the condition is called sex-linked. Y-linked disorders come from changes in the Y chromosome. They affect only males, because only males carry a Y chromosome. Mutations in this small chromosome can affect male sexual function and secondary sex characteristics. One example is Y-chromosome...

x-inactivation

Barr Bodies and X-Chromosome Balance

Barr bodies and X-chromosome balance help explain how female mammalian cells control gene activity from the X chromosome. The human X chromosome carries far more genes than the Y chromosome. Because males usually have one X chromosome and females have two, females would make twice as many of some proteins without a control system. To prevent that imbalance, female mammalian cells inactivate nearly all the genes on one X chromosome during early embryonic development. The inactive X condenses...

key terms and concepts

Learn how pedigree charts reveal dominant, recessive, autosomal, and sex-linked inheritance, plus carrier status and future disease risk in families.

Reading Family Traits in Pedigrees | JoVE K12

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biology

Tennessee Academic Standards

High School

Heredity

BIO1.LS3.3

Biological Change: Unity and Diversity

BIO1.LS4.1

Virginia  Standards of Learning

HIgh School

Life Science

LS.10

LS.10.c

Minnesota Academic Standards in Science

2.1.1 9L.2.1.1.1

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New Jersey Student Learning Standards for Science

Heredity: Inheritance and Variation of Traits

HS-LS3-3

Next Generation Science Standards

HS-LS3-1

HS-LS4-3

new-york-state-science-learning-standards

New York State Science Learning Standards

Inheritance and Variation of Traits

HS-LS3-1.

Florida Department of Education

SC.912.L.16

SC.912.L.16.1

What is Meiosis?

Meiosis is the process by which diploid cells divide to produce haploid daughter cells. In humans, each diploid cell contains 46 chromosomes, half from ...

Meiosis I

Meiosis II

Meiosis vs. Mitosis

Crossing Over

Crossing over is the exchange of genetic information between homologous chromosomes during prophase I of meiosis I. Genetic recombination gives rise to ...

Nondisjunction

Nondisjunction is the failure of homologous chromosomes or sister chromatids to separate correctly and move to the opposite poles of the cells. This ...

Spermatogenesis

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Oogenesis

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Fertilization

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Gastrulation

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Neurulation

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Cell Migration

Cell migration, the process by which cells move from one location to another, is essential for the proper development and viability of organisms ...

Determination

During embryogenesis, cells become progressively committed to different fates through a two-step process: specification followed by determination. ...

Use models to explain how DNA is passed from parents to offspring through the processes of meiosis and fertilization in sexual reproduction.

LS.Bio.6.1

Mutations

Mutations are changes in the sequence of DNA. These changes can occur spontaneously or they can be induced by exposure to environmental factors. Mutations ...

genome-size-and-the-evolution-of-new-genes

Genome Size and the Evolution of New Genes

types-of-genetic-transfer-between-organisms

Types of Genetic Transfer Between Organisms

Base-pairing and DNA Repair

The DNA Replication Fork

Lagging Strand Synthesis

The Replisome

Proofreading

Synthesis of new DNA molecules is carried out by the enzyme DNA polymerase, which adds nucleotides on the daughter strand complementary to the template ...

Replication in Prokaryotes

DNA replication has three main steps: initiation, elongation, and termination. Replication in prokaryotes begins when initiator proteins bind to the ...

Replication in Eukaryotes

In eukaryotic cells, DNA replication is highly conserved and tightly regulated. Multiple linear chromosomes must be duplicated with high fidelity before ...

Overview of DNA Repair

Base Excision Repair

Nucleotide Excision Repair

DNA Distortion and Damage
Cells are regularly exposed to mutagens&#8212;factors in the environment that can damage DNA and generate mutations. UV ...

Mismatch Repair

Organisms are capable of detecting and fixing nucleotide mismatches that occur during DNA replication. This sophisticated process requires identifying the ...

Fixing Double-strand Breaks

Homologous Recombination

Gene Conversion

Restarting Stalled Replication Forks

Construct an explanation to summarize how inheritable genetic variations may result from: new genetic combinations in meiosis, mutations during replication, or mutations caused by environmental factors.

LS.Bio.6.2

An Overview of Genetic Analysis

An organism&#8217;s physical traits, or phenotype, are a product of its genotype, which is the combination of alleles (gene variants) inherited from its ...

Genetic Crosses

To dissect genetic processes or create organisms with novel suites of traits, scientists can perform genetic crosses, or the purposeful mating of two ...

Punnett Squares

Monohybrid Crosses

Dihybrid Crosses

Trihybrid Crosses

Trihybrid Crosses
Some of Mendel&#8217;s crosses examined three pairs of contrasting characteristics. Such a cross is called a trihybrid cross. A ...

Law of Independent Assortment

Chi-square Analysis

The chi-square test is a statistical hypothesis test. It is used to check whether there is a significant difference between an expected value and an ...

Multiple Allele Traits

Incomplete Dominance

Gregor Mendel&#39;s work (1822 - 1884) was primarily focused on pea plants. Through his initial experiments, he determined that every gene in a diploid ...

Lethal Alleles

Agouti: A Lethal Allele
Lucien Cu&#233;not discovered lethal alleles in 1905 while studying the inheritance of coat color in mice. The agouti gene is ...

Polygenic Traits

background-and-environment-affect-phenotype

Background and Environment Affect Phenotype

Although the genetic makeup of an organism plays a major role in determining the phenotype, there are also several environmental factors, such as ...

Use mathematics and computational thinking to predict the variation and distribution of expressed traits based on: Mendelian inheritance, co-dominance, incomplete dominance, multiple alleles, and sex-linked inheritance.

LS.Bio.7.1

Probability Laws

Overview

The probability of inheriting a trait can be calculated using the sum and product rules. The sum rule is used to calculate the probability of ...

The Concept of Multiple Allelism

Multiple allelism describes genes that exist in three or more allelic forms. Although diploid organisms, like humans, ...

Analyze and interpret data to explain how polygenic traits result in a wide range of phenotypes.

Pleiotropy

Pleiotropy is the phenomenon in which a single gene impacts multiple, seemingly unrelated phenotypic traits. For example, defects in the SOX10 gene cause ...

Nature and Nurture

Many human characteristics, like height, are shaped by both nature&mdash;in other words, by our genes&mdash;and by nurture, or our environment. For ...

Construct an explanation to summarize how traits result from interactions of genetic factors (multiple genes and/or alleles) and environmental factors.

LS.Bio.7.3

PCR: The Polymerase Chain Reaction

The polymerase chain reaction, or PCR, is a technique used to amplify DNA through thermocycling &#8211; cyles of temperature changes at fixed time ...

DNA Gel Electrophoresis

DNA gel electrophoresis is a technique used for the detection and separation of DNA molecules. An electric field is applied to a gel matrix comprised of ...

Analyze and interpret data to compare DNA samples.

LS.Bio.8.1

Understand genetic mechanisms for variation.

Reading Family Traits in Pedigrees

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