Name: genotype, phenotype, and inheritance
Uploaded: 2026-08-26T08:19:10.450Z
Duration: 2 min 25 s
Channel: JoVE

K12 Standards

Virginia  Standards of Learning

HIgh School

Life Science

LS.10

LS.10.c

Genetic Lingo

A gene is a segment of DNA located on a chromosome that carries genetic information. Alleles are different forms of the same gene.In diploid organisms, one allele for each gene is inherited from each parent. The specific location of a gene or allele on a chromosome is called a locus. The two inherited alleles are located at the same locus on a pair of homologous chromosomes, with one chromosome inherited from the mother and the other from the father.This pair of alleles is called the genotype for that gene. The observable trait, or phenotype, such as eye color, is influenced by this inherited combination.Several genes influence human eye color. But for simplicity, consider a one-gene model with two alleles, brown and blue, represented by uppercase B and lowercase b, respectively, to explain how genotype relates to phenotype.If both alleles are identical, such as two brown alleles or two blue alleles, the genotype is called homozygous. On the other hand, if the alleles are different, such as one brown allele and one blue allele, the genotype is called heterozygous.The same phenotype, such as brown eyes, can result from different genotypes. For example, both, a homozygous brown genotype and a heterozygous genotype, can produce brown eyes.This happens because some alleles are dominant, meaning they are expressed even when only one copy is present. Other alleles are recessive, meaning they are expressed only when two copies of the recessive allele are present.In this example, the brown allele is dominant and is written with an uppercase B, while the blue allele is recessive and is written with a lowercase b. So, both the homozygous brown genotype and the heterozygous genotype result in brown eyes.The recessive allele affects the phenotype only in a homozygous recessive genotype. So, blue eyes appear only when both alleles are recessive.

genetic lingo

An organism is diploid if it inherits two variants, or alleles, of each gene, one from each parent. These two alleles constitute the genotype for a given gene. The term genotype is also used to refer to an organism&#x2019;s complete set of genes. A diploid organism with two identical alleles has a homozygous genotype, whereas two different alleles indicate a heterozygous genotype. Observable traits arising from genotypes are called phenotypes, which can also be influenced by environmental factors. An allele is dominant if only one copy is needed to manifest an associated phenotype and recessive if two copies are required for phenotypic expression.Alleles Can Influence Phenotypes Diploid organisms, including humans, most other animals, and many plants, have a duplicate set of chromosomes in somatic (non-sex) cells. These chromosome duplicates are homologous, with similar lengths, centromere positions, and gene locations. Diploid organisms inherit two versions of each gene, one from each parent. These two gene variants, or alleles, are situated at the same relative locus, or position, on two homologous chromosomes. Each chromosome contains many genetic loci, and there are often several possible alleles of a given gene.The two alleles inherited by a diploid organism constitute its genotype at the locus. The term genotype also refers to an organism&#x2019;s total set of genes. Different genotypes can result in distinct phenotypes, or observable characteristics (e.g., eye color). Phenotypes emerge as a result of genotypes, although multiple genotypes can cause the same phenotype. Phenotypes are also often influenced by environmental factors.A Genotype May Consist of Two Identical or Distinct Alleles For a given gene, the two inherited alleles may have either identical or distinct nucleotide sequences. An organism with two identical alleles has a homozygous genotype (or is a homozygote). An organism with two different alleles has a heterozygous genotype (i.e., is a heterozygote). If the two alleles are different (heterozygous genotype), but only one affects the phenotype, the allele that influences the phenotype is dominant. The other allele, which does not affect the phenotype, is recessive.Originally, eye color was thought to be determined by a single gene, and thus it is often used to illustrate genetic dominance (brown eyes) and recessiveness (blue eyes). However, scientists discovered at least eight genes that regulate eye color. Although the OCA2 gene is responsible for nearly three-fourths of the variation in the blue-brown eye color spectrum, other genes occasionally modify or override these effects. Nonetheless, eye color can be a useful example to illustrate dominant and recessive alleles.In the following, we use the simplified eye color example to illustrate the relationship between genotype and phenotype. The allele for brown eyes is denoted B, and the allele for blue eyes is b. A heterozygote would have genotype Bb as a result of receiving a dominant allele from one parent and a recessive allele from the other. This individual would have brown eyes, the dominant phenotype. The dominant allele (B) overrides or &#x201C;hides&#x201D; instructions from the recessive allele for blue eyes. Thus, an individual with blue eyes would necessarily have the genotype bb, whereas an individual with brown eyes could have either genotype BB or Bb.Dominant and Recessive Disease Inheritance Patterns Are Related to Disease Risk Although most traits are controlled by multiple genes rather than a single causal gene, these principles can be useful for predicting the probability of important outcomes. For example, Huntington&#x27;s disease (HD) is a progressive, neurodegenerative condition that causes uncontrolled movements and cognitive and emotional disturbances. HD is considered a single-gene disorder because it is caused by a mutation in a single gene (HTT), although other genes do modify onset and progression. HD is caused by a dominant mutation, meaning that a single mutated allele leads to expression of the disease. If the parent has a normal and a mutated gene variant, the offspring has a 50% chance of receiving the mutated allele and developing the disease. HD also does not typically manifest until middle to late life. Thus, although the reality is unpleasant, a person with an affected parent can undergo genetic testing to determine if they have the causal allele and, in turn, inform their family planning.

Overview

An organism is diploid if it inherits two variants, or alleles, of each gene, one from each parent. These two alleles constitute the genotype ...

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Education

JoVE Core

Biology

Genetics

Classical and Modern Genetics

KEY TERMS AND CONCEPTS

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, or position, on homologous chromosomes. The two alleles at a locus make up an organism’s genotype for that gene. Genotype can also mean the organism’s complete set of genes.

Different genotypes can produce different phenotypes, which are the observable traits of an organism. Eye color is one example. Phenotypes can also be shaped by environmental factors, and more than one genotype can sometimes lead to the same phenotype.

For a given gene, the two alleles may be identical or different. A homozygous genotype has two identical alleles. A heterozygous genotype has two different alleles. If a heterozygote shows the effect of only one allele, that allele is dominant, and the other is recessive.

Brown and blue eye color are often used to show dominance and recessiveness. In this simplified example, B stands for the brown-eye allele and b stands for the blue-eye allele. A person with Bb has brown eyes because the dominant B allele hides the blue-eye instructions from b. A person with blue eyes must have bb, while a person with brown eyes can have BB or Bb.

These same ideas also help explain disease inheritance. Huntington disease is a progressive neurodegenerative condition that can cause uncontrolled movements and changes in thinking and mood. It is a single-gene disorder caused by a mutation in the HTT gene, although other genes can affect when it starts and how it progresses. The mutation is dominant, so one mutated allele can cause the disease. If a parent has one normal allele and one mutated allele, each child has a 50% chance of inheriting the mutation. Because Huntington disease often appears in middle to late life, genetic testing can help affected families with planning.

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...

pedigree analysis

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...

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 genotypes, alleles, dominant and recessive traits, and Huntington disease inheritance connect genes to visible traits and disease risk.

Genotype, Phenotype, and Inheritance | JoVE K12

JoVE Core series brings biology to life through over 300 concise and easy-to-understand animated video lessons that explain key concepts in biology, plus more than 150 scientist-in-action videos that show actual research experiments conducted in today’s laboratories.

biology

Next Generation Science Standards

High School

heredity-inheritance-and-variation-of-traits

Heredity: Inheritance and Variation of Traits

HS-LS3-1

Florida Department of Education

SC.912.L.16

SC.912.L.16.1

new-york-state-science-learning-standards

New York State Science Learning Standards

Inheritance and Variation of Traits

HS-LS3-1.

The DNA Helix

Overview

Deoxyribonucleic acid, or DNA, is the genetic material responsible for passing traits from generation to generation in all organisms and most ...

DNA Packaging

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Eukaryotes have large genomes compared to prokaryotes. In order to fit their genomes into a cell, eukaryotes must pack their DNA tightly inside ...

Organization of Genes

Overview

The genomes of eukaryotes can be structured in several functional categories. A strand of DNA is comprised of genes and intergenic regions. ...

Replication in Prokaryotes

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

Replication in Eukaryotes

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

Proofreading

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Mutations

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

Transcription

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Translation

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Bacterial Transformation

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The Central Dogma

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The central dogma of biology states that information encoded in the DNA is transferred to messenger RNA (mRNA), which then directs the synthesis ...

Transcription Factors

Tissue-specific transcription factors contribute to diverse cellular functions in mammals. For example, the gene for beta globin, a major component of ...

RNA Structure

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RNA Stability

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Types of RNA

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MicroRNAs

MicroRNA (miRNA) are short, regulatory RNA transcribed from introns&mdash;non-coding regions of a gene&mdash;or intergenic regions&mdash;stretches of DNA ...

RNA Splicing

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Epigenetic Regulation

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RNA Interference

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Operons

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Proteins: From Genes to Degradation

The student will investigate and understand that organisms reproduce and transmit genetic information to new generations. Key ideas include DNA has a role in making proteins that determine organism traits;

LS.10.a

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 is a carefully orchestrated set of cell divisions, the goal of which&#x2014;in humans&#x2014;is to produce haploid sperm or eggs, each containing ...

Meiosis II

Meiosis II is the second and final stage of meiosis. It relies on the haploid cells produced during meiosis I, each of which contain only 23 ...

Crossing Over

Unlike mitosis, meiosis aims for genetic diversity in its creation of haploid gametes. Dividing germ cells first begin this process in prophase I, where ...

Nondisjunction

During meiosis, chromosomes occasionally separate improperly. This occurs due to failure of homologous chromosome separation during meiosis I or failed ...

The student will investigate and understand that organisms reproduce and transmit genetic information to new generations. Key ideas include the role of meiosis is to transfer traits to the next generation; and

LS.10.b

Punnett Squares

Overview

A Punnett square displays the possible genotypes offspring can inherit from two parental genotypes. If a trait&#x2019;s inheritance pattern ...

Monohybrid Crosses

Overview

In the 1850s and 1860s, Gregor Mendel investigated inheritance by performing monohybrid crosses in pea plants. He crossed two plants that were ...

Dihybrid Crosses

Overview

To determine whether traits are inherited together or separately, Gregor Mendel crossed pea plants that differed in two traits. These parental ...

Law of Segregation

When crossing pea plants, Mendel noticed that one of the parental traits would sometimes disappear in the first generation of offspring, called the F1 ...

Law of Independent Assortment

While Mendel&#x2019;s Law of Segregation states that the two alleles for one gene are separated into different gametes, a different question of how ...

Test Cross

Alleles are different forms of the same gene. Humans and other diploid organisms inherit two alleles of every gene, one from each parent.

An allele is ...

Pedigree Analysis

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 ...

X-linked Traits

In most mammalian species, females have two X sex chromosomes and males have an X and Y. As a result, mutations on the X chromosome in females may be ...

Sex-linked Disorders

Like autosomes, sex chromosomes contain a variety of genes necessary for normal body function. When a mutation in one of these genes results in biological ...

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 ...

The student will investigate and understand that organisms reproduce and transmit genetic information to new generations. Key ideas include Punnett squares are mathematical models used to predict the probability of traits in offspring.

Genotype, Phenotype, and Inheritance

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