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

- Gli alleli sono diverse
forme dello stesso gene.

Se ne riceve uno da ciascun genitore,

risultando in un organismo diploide,

con due alleli in ogni posto
per ciascun gene coinvolto.

Ciascun paio è noto come
genotipo di un gene particolare

e l'espressione fisica osservabile,

il fenotipo, come il colore degli occhi,

è determinato dalla
combinazione ereditata.

In questo caso, uno dei
geni contiene due alleli

per i potenziali colori marrone e blu.

Se entrambe le forme sono identiche,

il genotipo si chiama omozigote.

Se la coppia è differente,
il genotipo è eterozigote.

Curiosamente, lo stesso
fenotipo degli occhi marroni

può venire da genotipi differenti.

Questo è perché l'allele
dominante, il marrone,

indicato con la maiuscola, si esprime

con priorità sull'allele recessivo, blu,

indicato con lettera minuscola.

L'unico modo in cui un allele
recessivo può essere espresso

è se entrambi sono recessivi.

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

linguaggio genetico

<h4>Panoramica</h4>

Un organismo è diploide se eredita due varianti, o alleli, di ogni gene, una da ogni genitore. Questi due alleli costituiscono il genotipo per un dato gene. Il termine genotipo è anche usato per riferirsi all'insieme completo di geni di un organismo. Un organismo diploide con due alleli identici ha un genotipo omozigote, mentre due diversi alleli indicano un genotipo eterozigote. I tratti osservabili derivanti dai genotipi sono chiamati fenotipi, che possono anche essere influenzati da fattori ambientali. Un allele è dominante se è necessaria una sola copia per manifestare un fenotipo associato e recessiva se sono necessarie due copie per l'espressione fenotipica.

<h4>Gli alleli possono influenzare i fenotipi</h4>

Gli organismi diploidi, tra cui gli esseri umani, la maggior parte degli altri animali e molte piante, hanno una serie duplicata di cromosomi in cellule somatiche (non sessuali). Questi duplicati cromosomici sono omologhi, con lunghezze simili, posizioni dei centrimeri e posizioni geniche. Gli organismi diploidi ereditano due versioni di ciascun gene, una per ogni genitore. Queste due varianti geniche, o alleli, si trovano nello stesso locus relativo, o posizione, su due cromosomi omologhi. Ogni cromosoma contiene molti loci genetici, e ci sono spesso diversi possibili alleli di un dato gene.

I due alleli ereditati da un organismo diploide ne costituiscono il genotipo allocus. Il termine genotipo si riferisce anche all'insieme totale di geni di un organismo. Genotipi diversi possono portare a fenotipi distinti o caratteristiche osservabili (ad esempio, colore degli occhi). I fenotipi emergono come risultato di genotipi, anche se più genotipi possono causare lo stesso fenotipo. I fenotipi sono spesso influenzati da fattori ambientali.

<h4>Un genotipo può consistere in due alleli identici o distinti</h4>

Per un dato gene, i due alleli ereditati possono avere sequenze nucleotidiche identiche o distinte. Un organismo con due alleli identici ha un genotipo omozigote(o è un omozigote). Un organismo con due diversi alleli ha un genotipo eterozigote (cioè, è un eterozigote). Se i due alleli sono diversi (genotipo eterozigote), ma solo uno colpisce il fenotipo, l'allele che influenza il fenotipo è dominante. L'altro allele, che non influisce sul fenotipo, è recessivo.

Originariamente, il colore degli occhi è stato pensato per essere determinato da un singolo gene, e quindi è spesso usato per illustrare il dominio genetico (occhi marroni) e la recessività (occhi blu). Tuttavia, gli scienziati hanno scoperto almeno otto geni che regolano il colore degli occhi. Sebbene il gene OCA2 sia responsabile di quasi i tre quarti della variazione nello spettro dei colori degli occhi blu-marrone, altri geni occasionalmente modificano o sostituiscono questi effetti. Tuttavia, il colore degli occhi può essere un utile esempio per illustrare alleli dominanti e recessivi.

Di seguito, utilizziamo l'esempio di colore degli occhi semplificato per illustrare la relazione tra genotipo e fenotipo. L'allele per gli occhi marroni è indicato B, e l'allele per gli occhi azzurri è b. Un eterozigote avrebbe il genotipo Bb come risultato di ricevere un allele dominante da un genitore e un allele recessivo dall'altro. Questo individuo avrebbe gli occhi marroni, il fenotipo dominante. L'allele dominante (B) prevale o "nasconde" le istruzioni dall'allele recessivo per gli occhi azzurri. Così, un individuo con gli occhi azzurri avrebbe necessariamente il genotipo bb, mentre un individuo con gli occhi marroni potrebbe avere genotipo BB o Bb.

<h4>I modelli di ereditarietà delle malattie dominanti e recessive sono correlati al rischio di malattia</h4>

Anche se la maggior parte dei tratti sono controllati da più geni piuttosto che da un singolo gene causale, questi principi possono essere utili per prevedere la probabilità di risultati importanti. Ad esempio, la malattia di Huntington (HD) è una condizione progressiva e neurodegenerativa che causa movimenti incontrollati e disturbi cognitivi ed emotivi. La MH è considerata un singolo disturbo genico perché è causata da una mutazione in un singolo gene (HTT), anche se altri geni modificano l'insorgenza e la progressione. La MH è causata da una mutazione dominante, il che significa che un singolo allele mutato porta all'espressione della malattia. Se il genitore ha una variante genica normale e mutata, la prole ha una probabilità del 50% di ricevere l'allele mutato e sviluppare la malattia. Anche la MH in genere non si manifesta fino alla metà alla tarda vita. Così, anche se la realtà è sgradevole, una persona con un genitore affetto può sottoporsi a test genetici per determinare se hanno l'allele causale e a sua volta informare la loro pianificazione familiare.

Linguaggio genetico

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 ...

Education

Didattica

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Biology

Biologia

Genetics

Genetica

Classical and Modern Genetics

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KEY TERMS AND CONCEPTS

TERMINI E CONCETTI CHIAVE

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...

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...

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...

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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JoVE Core Biologia illustra i concetti chiave della biologia grazie a oltre 300 video-lezioni animate, concise e di facile comprensione. Inoltre, negli oltre 150 video di "scienziati in azione", i concetti scientifici vengono applicati e dimostrati da ricercatori attraverso esperimenti in laboratorio.

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.

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LS.10.a

What is Meiosis?

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Meiosis I

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Meiosis II

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Nondisjunction

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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

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Law of Independent Assortment

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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

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Nature and Nurture

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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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