Name: genotype, phenotype, and inheritance
Uploaded: 2019-03-11T09:21:16.000Z
Duration: 1 min 11 s
Channel: JoVE

K12 Standards

Virginia  Standards of Learning

HIgh School

Life Science

LS.10

LS.10.c

Genetic Lingo

Les allèles sont des variantes d'un même gène. 
Chaque parent en transmet un,ce qui donne un organisme diploïde. 
Il y a deux allèles présents pour chaque gène. 
Chaque paire forme le génotype d'un gène particulier. 
Son expression physique est le phénotype,comme la couleur des yeux. 
Il est déterminé par la combinaison transmise. 
Dans ce cas, un des gènes contient deux allèlespour les couleurs possibles brun et bleu. 
Si les deux formes sont identiques,le génotype est homozygote. 
Si la paire est différente, il est hétérozygote. 
Le phénotype pour les yeux bruns peut s'exprimerà partirde deux génotypes différents. 
En fait, l'allèle dominant, brun,représenté par « B » majuscule, est plus fortque l'allèle récessif, bleu,représenté par un « b » minuscule. 
Pour qu'un allèle récessif s'exprime,il faut une paire d'allèles récessifs.

Fay, David et Andy Spencer. Mutations dominantes. WormBook, 2006. [<a href="https://www.ncbi.nlm.nih.gov/books/NBK19699/ » target="__blank">Source</a>].

vocabulaire de génétique

<h4>Aperçu</h4>
 
 Un organisme est diploïde s’il hérite de deux variantes, ou allèles, de chaque gène, une de chaque parent. Ces deux allèles constituent le génotype d’un gène donné. Le terme génotype est également utilisé pour désigner l’ensemble complet des gènes d’un organisme. Un organisme diploïde avec deux allèles identiques a un génotype homozygote, tandis que deux allèles différents indiquent un génotype hétérozygote. Les traits observables issus des génotypes s’appellent des phénotypes, qui peuvent également être influencés par des facteurs environnementaux. Un allèle est dominant si une seule copie est nécessaire pour que se manifeste un phénotype associé, et il est récessif si deux copies sont nécessaires pour l’expression phénotypique.
 
 <h4>Les allèles peuvent influencer les phénotypes</h4>
 
 Les organismes diploïdes, y compris les humains, la plupart des autres animaux et de nombreuses plantes, ont un ensemble double de chromosomes dans les cellules somatiques (non sexuelles). Ces doubles chromosomes sont homologues avec des longueurs, des positions des centromères et des emplacements de gènes semblables. Les organismes diploïdes héritent de deux versions de chaque gène, une de chaque parent. Ces deux variantes génétiques, ou allèles, sont situées au niveau du même locus relatif, ou position, sur deux chromosomes homologues. Chaque chromosome contient de nombreux locus génétiques, et il y a souvent plusieurs allèles possibles d’un gène donné.
 
 Les deux allèles dont a hérités un organisme diploïde constituent son génotype au locus. Le terme génotype fait également référence à l’ensemble total des gènes d’un organisme. Différents génotypes peuvent entraîner des phénotypes distincts, ou des caractéristiques observables distinctes (p. ex., la couleur des yeux). Les phénotypes émergent à la suite de génotypes, bien que plusieurs génotypes puissent causer le même phénotype. Les phénotypes sont également souvent influencés par des facteurs environnementaux.
 
 <h4>Un génotype peut se composer de deux allèles identiques ou distincts</h4>
 
 Pour un gène donné, les deux allèles hérités peuvent avoir des séquences de nucléotides identiques ou distinctes. Un organisme avec deux allèles identiques a un génotype homozygote (ou lui-même est un homozygote). Un organisme avec deux allèles différents a un génotype hétérozygote (c.-à-d. est un hétérozygote). Si les deux allèles sont différents (génotype hétérozygote), mais qu’un seul influe sur le phénotype, l’allèle qui influence le phénotype est dominant. L’autre allèle, qui n’impacte pas le phénotype, est récessif.
 
 À l’origine, on pensait que la couleur des yeux était déterminée par un seul gène, et elle est donc souvent utilisée pour illustrer la dominance (les yeux bruns) et la récessivité génétique (les yeux bleus). Cependant, les scientifiques ont découvert au moins huit gènes qui régulent la couleur des yeux. Bien que le gène OCA2 soit responsable de près des trois quarts de la variation du spectre de couleurs des yeux bleu-brun, d’autres gènes modifient ou remplacent occasionnellement ces effets. Néanmoins, la couleur des yeux peut être un exemple utile pour illustrer les allèles dominants et récessifs.
 
 Dans ce qui suit, nous utilisons l’exemple simplifié de la couleur des yeux pour illustrer la relation entre le génotype et le phénotype. L’allèle pour les yeux bruns est noté B, et l’allèle pour les yeux bleus est b. Un hétérozygote aurait le génotype Bb après avoir reçu un allèle dominant d’un parent et un allèle récessif de l’autre. Cet individu aurait les yeux bruns, le phénotype dominant. L’allèle dominant (B) remplace ou “ cache ” les instructions de l’allèle récessif pour les yeux bleus. Ainsi, un individu avec les yeux bleus aurait nécessairement le génotype bb, alors qu’un individu avec les yeux bruns pourrait avoir soit le génotype BB, soit Bb.
 
 <h4>Les modèles héréditaires dominants et récessifs d’une maladie sont liés au risque de maladie</h4>
 
 Bien que la plupart des traits soient contrôlés par plusieurs gènes plutôt qu’un seul gène causal, ces principes peuvent être utiles pour prévoir la probabilité de résultats importants. Par exemple, la maladie de Huntington (MH) est une maladie neurodégénérative progressive qui provoque des mouvements incontrôlés et des perturbations cognitives et émotionnelles. La MH est considérée comme un seul trouble génétique parce qu’elle est causée par une mutation dans un seul gène (HTT), bien que d’autres gènes modifient l’apparition et la progression. La MH est causée par une mutation dominante, ce qui signifie qu’un seul allèle muté conduit à l’expression de la maladie. Si le parent a une variante du gène normale et une variante mutée, la progéniture a 50 % de chances de recevoir l’allèle muté et de développer la maladie. La MH ne se manifeste généralement pas avant le milieu ou à la fin de la vie adulte. Ainsi, bien que la réalité soit désagréable, les personne qui ont un parent impacté peuvent subir des tests génétiques pour déterminer si ils ont l’allèle causal et à leur tour informer le planning familial.

Vocabulaire de génétique

Aperçu

Un organisme est diploïde s’il hérite de deux variantes, ou allèles, de chaque gène, une de chaque parent. Ces deux allèles constituent le génotype ...

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Génétique classique et moderne

KEY TERMS AND CONCEPTS

TERMES ET CONCEPTS CLÉS

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

genetic lingo

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...

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...

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...

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...

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...

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%...

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,...

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-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.

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...

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...

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...

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

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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

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New York State Science Learning Standards

Inheritance and Variation of Traits

HS-LS3-1.

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LS.10.a

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LS.10.b

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 ...

Punnett Squares

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Monohybrid Crosses

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Dihybrid Crosses

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Law of Segregation

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Test Cross

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X-linked Traits

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Sex-linked Disorders

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Genotype, Phenotype, and Inheritance

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