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

- [Instructeur] Allelen zijn verschillende vormen van hetzelfde gen. Er komt er één van elke ouder, wat resulteert in een diploïde organisme, twee allelen op dezelfde locus voor elk betrokken gen. Elk paar wordt het genotype van een bepaald gen genoemd en de fysieke en observeerbare expressie, het fenotype, zoals de kleur van de ogen, wordt bepaald door de overgeërfde combinatie.

In dit geval bevat een van de genen twee allelen voor de potentiële kleuren bruin en blauw. Als beide vormen identiek zijn, wordt het genotype homozygoot genoemd. Als de paren verschillend zijn, is het genotype heterozygoot.

Interessant is dat hetzelfde fenotype, zoals bruine ogen, kan worden uitgedrukt uit verschillende genotypes. Dit komt doordat het dominante allel, bruin, getoond als hoofdletter, uitgedrukt wordt over het recessieve allel, blauw, geschreven als een kleine letter. Vandaar dat de enige manier waarop een recessief allel uitgedrukt kan worden als beide kopieën recessief zijn.

genetisch jargon

<h4>Overzicht</h4>

Een organisme is diploïde als het twee varianten, of allelen, van elk gen erft, één van elke ouder. Deze twee allelen vormen het genotype voor een bepaald gen. De term genotype wordt ook gebruikt om te verwijzen naar de complete set genen van een organisme. Een diploïde organisme met twee identieke allelen heeft een homozygoot genotype, terwijl twee verschillende allelen wijzen op een heterozygoot genotype. Waarneembare eigenschappen die voortkomen uit genotypen worden fenotypen genoemd, die ook kunnen worden beïnvloed door omgevingsfactoren. Een allel is dominant als er slechts één kopie nodig is om een geassocieerd fenotype te manifesteren en recessief als er twee kopieën nodig zijn voor fenotypische expressie.

<h4>Allelen kunnen fenotypes beïnvloeden</h4>

Diploïde organismen, waaronder mensen, de meeste andere dieren en veel planten, hebben een dubbele set chromosomen in somatische (niet-geslachts)cellen. Deze chromosoomduplicaten zijn homoloog, met vergelijkbare lengtes, centromeerposities en genlocaties. Diploïde organismen erven twee versies van elk gen, één van elke ouder. Deze twee genvarianten, of allelen, bevinden zich op dezelfde relatieve locus of positie op twee homologe chromosomen. Elk chromosoom bevat veel genetische loci, en er zijn vaak meerdere mogelijke allelen van een bepaald gen.

De twee allelen die door een diploïde organisme worden geërfd, vormen het genotype op de locus. De term genotype verwijst ook naar de totale set genen van een organisme. Verschillende genotypen kunnen verschillende fenotypes of waarneembare kenmerken (bijvoorbeeld oogkleur) veroorzaken. Fenotypes ontstaan als gevolg van genotypen, hoewel meerdere genotypen hetzelfde fenotype kunnen veroorzaken. Fenotypes worden ook vaak beïnvloed door omgevingsfactoren.

<h4>Een genotype kan bestaan uit twee identieke of verschillende allelen</h4>

Voor een bepaald gen kunnen de twee erfelijke allelen identieke of verschillende nucleotidesequenties hebben. Een organisme met twee identieke allelen heeft een homozygoot genotype (of is homozygoot). Een organisme met twee verschillende allelen heeft een heterozygoot genotype (dat wil zeggen, het is heterozygoot). Als de twee allelen verschillend zijn (heterozygoot genotype), maar slechts één allel invloed heeft op het fenotype, is het allel dat het fenotype beïnvloedt dominant. Het andere allel, dat het fenotype niet beïnvloedt, is recessief.

Oorspronkelijk werd gedacht dat oogkleur door één enkel gen werd bepaald, en daarom wordt het vaak gebruikt om genetische dominantie (bruine ogen) en recessiviteit (blauwe ogen) te illustreren. Wetenschappers ontdekten echter minstens acht genen die de oogkleur reguleren. Hoewel het OCA2-gen verantwoordelijk is voor bijna driekwart van de variatie in het blauwbruine oogkleurenspectrum, wijzigen of overschrijven andere genen deze effecten af en toe. Niettemin kan oogkleur een nuttig voorbeeld zijn om dominante en recessieve allelen te illustreren.

Hieronder gebruiken we het vereenvoudigde voorbeeld van oogkleur om de relatie tussen genotype en fenotype te illustreren. Het allel voor bruine ogen wordt aangeduid met B, en het allel voor blauwe ogen is b. Een heterozygoot zou genotype Bb hebben als gevolg van het ontvangen van een dominant allel van de ene ouder en een recessief allel van de andere. Deze persoon zou bruine ogen hebben, het dominante fenotype. Het dominante allel (B) overschrijft of "verbergt" instructies van het recessieve allel voor blauwe ogen. Een individu met blauwe ogen zou dus noodzakelijkerwijs het genotype bb hebben, terwijl een individu met bruine ogen genotype BB of Bb zou kunnen hebben.

<h4>Dominante en recessieve ziekte-overervingspatronen houden relatie met ziekterisico</h4>

Hoewel de meeste eigenschappen worden gecontroleerd door meerdere genen in plaats van door één enkel causaal gen, kunnen deze principes nuttig zijn voor het voorspellen van de waarschijnlijkheid van belangrijke uitkomsten. De ziekte van Huntington (ZvH) is bijvoorbeeld een progressieve, neurodegeneratieve aandoening die ongecontroleerde bewegingen en cognitieve en emotionele stoornissen veroorzaakt. De ZvH wordt beschouwd als een aandoening met één gen, omdat deze wordt veroorzaakt door een mutatie in één enkel gen (HTT), hoewel andere genen het begin en de progressie beïnvloeden. De ZvH wordt veroorzaakt door een dominante mutatie, wat betekent dat een enkel gemuteerd allel leidt tot de expressie van de ziekte. Als een ouder een normale en een gemuteerde genvariant heeft, heeft het nageslacht 50% kans om het gemuteerde allel te ontvangen en de ziekte te ontwikkelen. De ZvH manifesteert zich doorgaans pas op middelbare tot late leeftijd. Hoewel de realiteit onaangenaam is, kan een persoon met een getroffen ouder genetische tests ondergaan om te bepalen of hij of zij het causale allel heeft, wat op zijn beurt hun gezinsplanning kan beïnvloeden.

Genetisch jargon

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

JoVE Core

Biology

Biologie

Genetics

Genetica

Classical and Modern Genetics

Klassieke en moderne genetica

KEY TERMS AND CONCEPTS

BELANGRIJKE TERMEN EN CONCEPTEN

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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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

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LS.10.b

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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Genotype, Phenotype, and Inheritance

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