Name: test cross in genetic inheritance
Uploaded: 2021-04-07T12:12:00.000Z
Duration: 1 min 50 s
Channel: JoVE

- [Narrador] Una cruza
de prueba es una t&#xE9;cnica

que puede usarse para
determinar el genotipo

de un organismo, expresando
un rasgo dominante,

como, el color purpura en
las flores de una planta

de guisantes.

Porque la versi&#xF3;n dominante,
o alelo de un gen,

siempre se expresara
sobre el alelo recesivo,

organismos con el genotipo
homocigoto-dominante,

dos alelos dominantes aparecer&#xE1;n igual

que organismos con el
genotipo heterocigoto,

un alelo dominante.

Una planta de guisantes de flores purpura

de genotipo desconocido,

puede cruzarse con una
planta de guisantes que tiene

el fenotipo recesivo, flores blancas.

Y as&#xED; se sabe que tiene

el genotipo homocigoto-recesivo,
p peque&#xF1;a, p peque&#xF1;a.

En un escenario, si toda la descendencia

de la cruza de prueba,

exhibe el fenotipo dominante,
el padre desconocido

debe ser homocigoto-dominante
para flores purpura.

Toda la descendencia es heterocigoto,

recibiendo un alelo
recesivo del padre recesivo,

y un alelo dominante del otro padre.

Sin embargo, si la descendencia
incluye un numero igual

de organismos exhibiendo
el fenotipo dominante

y organismos exhibiendo
el fenotipo recesivo,

el padre desconocido
debe ser heterocigoto.

Toda la descendencia aun
recibe sus alelos recesivos,

del padre recesivo.

La mitad de la descendencia
recibe un alelo dominante,

del padre heterocigoto,

y exhibe el fenotipo dominante,

mientras que la otra mitad
recibe una segunda copia

del alelo recesivo del padre heterocigoto,

y exhibe el fenotipo recesivo.

Miko, Ilona. 2008. "Cruces de prueba". Educación para la Naturaleza 1 (1): 136. [<a href="https://www.nature.com/scitable/topicpage/test-crosses-585">Fuente</a>]

Reid, James B. y John J. Ross. 2011. "Los genes de Mendel: hacia una caracterización molecular completa" Genética 189 (1): 3–10. [<a href="https://doi.org/10.1534/genetics.111.132118">Fuente</a>]

cruzamiento de prueba

Test Cross

Los alelos son diferentes formas del mismo gen. Los humanos y otros organismos diploides heredan dos alelos de cada gen, uno de cada padre. Un alelo es recesivo si sus efectos est&#xE1;n enmascarados por otro alelo en la misma ubicaci&#xF3;n gen&#xE9;tica. Por ejemplo, las plantas de guisantes pueden tener flores moradas o blancas. En este caso, las flores blancas son recesivas ya que una sola copia del alelo de las flores moradas dar&#xE1; como resultado una planta con flores moradas, incluso si tambi&#xE9;n tienen el alelo de las flores blancas. Si un organismo exhibe un rasgo recesivo conocido, determinar el genotipo del organismo (su par de alelos heredados) es simple. S&#xF3;lo un genotipo, pp (dos alelos recesivos), produce flores blancas. Para un organismo con un rasgo dominante, como una planta de guisantes con flores violetas, determinar el genotipo no es tan sencillo. Dos genotipos, PP y Pp, producen flores de color violeta. Los cient&#xED;ficos utilizan cruces de prueba para determinar los genotipos de organismos que exhiben rasgos dominantes simples. Un cruce de prueba implica reproducir o cruzar el organismo en cuesti&#xF3;n con uno que muestra la contraparte recesiva de su rasgo dominante. En un cruce de prueba para una planta de guisante con flores moradas, la planta se cruza con una planta de guisante que tiene flores blancas (genotipo pp). El color de la flor de la descendencia resultante revela si el padre con flores moradas es homocigoto (PP) o heterocigoto (Pp). Si la planta es homocigota, toda la descendencia heredar&#xE1; uno de sus alelos P dominantes y uno de los alelos p recesivos del otro padre. Dado que los alelos dominantes enmascaran los alelos recesivos, toda la descendencia tendr&#xE1; flores de color p&#xFA;rpura, el rasgo dominante. Sin embargo, si la planta es heterocigota, alrededor del 50% de la descendencia heredar&#xE1; su alelo p recesivo, junto con otro alelo recesivo del otro progenitor. Por lo tanto, aproximadamente la mitad de la descendencia de este cruce tendr&#xE1; flores blancas. De esta manera, los cruces de prueba pueden revelar genotipos parentales desconocidos.

Cruzamiento de prueba

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 ...

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Education

Educación

JoVE Core

Molecular Biology

Biología Molecular

Unit 2

Unidad 2

Analyzing Gene Expression and Function

Análisis de la expresión y función génica

KEY TERMS AND CONCEPTS

TÉRMINOS Y CONCEPTOS CLAVE

test cross in genetic inheritance

A test cross is a genetics tool used to determine the genotype of an organism with a dominant trait. It helps reveal whether the dominant individual is homozygous or heterozygous by crossing it with a recessive individual.

The outcome of the cross shows the hidden genotype. If any offspring show the recessive trait, the dominant parent must carry one recessive allele. If all offspring show the dominant trait, the dominant parent is likely homozygous dominant.

Test crosses are common in basic inheritance studies. They help students connect visible traits to the alleles behind them and make predictions about offspring using simple genetic crosses.

Test Cross in Genetic Inheritance

in vitro mutagenesis

In Vitro Mutagenesis for Gene Analysis

In vitro mutagenesis is a lab method used to change DNA and study gene function. It helps scientists test how specific DNA changes affect a gene’s activity and the traits it controls. A common approach is to make a known change in a DNA sequence and then examine the result. This can be done by deleting, inserting, or altering selected bases in a gene. The method is useful for linking a DNA change to a biological effect. Researchers use in vitro mutagenesis in molecular biology, genetics, and...

genetic screens

Using Genetic Screens to Find Disease Genes

Genetic screens are tools used to find genes and mutations linked to specific traits. They are also used to identify people or groups at risk for genetic diseases. That can support early intervention, targeted therapy, and reproductive choices. Forward genetic screens, also called classical screens, start with random DNA changes in an organism. Researchers may use radiation, mutagens, or added bases to create mutations that lead to visible phenotype changes. The mutant is then inbred so...

test cross

A test cross is a genetics tool used to determine the genotype of an organism with a dominant trait. It helps reveal whether the dominant individual is homozygous or heterozygous by crossing it with a recessive individual. The outcome of the cross shows the hidden genotype. If any offspring show the recessive trait, the dominant parent must carry one recessive allele. If all offspring show the dominant trait, the dominant parent is likely homozygous dominant. Test crosses are common in basic...

complementation tests

Using Crosses to Group Mutations

A complementation test uses a simple cross to find out whether two mutations are in the same gene or in different genes. It helps show how mutations are arranged on chromosomes. Edward Lewis first performed this test in the 1940s while studying fruit flies. To do the test, organisms heterozygous for different mutations are crossed pairwise in all combinations. If the mutations are in different genes, they can complement each other. In that case, each mutation provides the missing genetic...

single nucleotide polymorphisms-snps

SNPs as Genetic Markers and Variants

Single nucleotide polymorphisms, or SNPs, are small DNA changes at one specific genomic position. They are the most common type of sequence variation in the human genome. A point mutation counts as an SNP when it appears in more than 1% of the population.

bacterial transformation

Bacterial Transformation in the Lab

Bacterial transformation is a lab method used to move new DNA into bacteria. Scientists use it to change how bacteria behave or to help them carry a gene of interest. In high school biology, this process is often shown with plasmids, which are small circular DNA molecules. During transformation, bacteria take up DNA from their surroundings. The new DNA can then be used by the cell, depending on the experiment. This technique is an important part of genetic engineering and is widely used in...

transgenic organisms

Making Transgenic Organisms

Transgenic organisms are living things with DNA added from another organism. A transgene is the inserted gene. Scientists use this method to change an organism’s traits and to study how genes work. To make a transgenic organism, researchers first identify the gene they want to add. They then place that gene into the target organism’s DNA. Once the gene is integrated, the organism can pass it to new cells as it grows. This approach is useful in biology because it helps scientists analyze gene...

reproductive cloning

Cloning an Organism by Reproduction

Reproductive cloning creates a new organism that is genetically the same as the donor. It is different from cloning genes or cells because the goal is to make a whole living individual. This process usually relies on somatic cell nuclear transfer. In this method, the nucleus from a body cell is placed into an egg cell that has had its own nucleus removed. The egg can then develop into an embryo with DNA from the donor cell. Reproductive cloning is used to produce a copy of an organism, such...

crispr

CRISPR Gene Editing Basics

CRISPR is a gene editing tool that helps scientists make targeted changes to DNA. It uses a guide system to find a chosen sequence and a cutting protein to act at that spot. This method is based on a natural defense system found in bacteria. In high school biology, it is often studied as a way to see how genes can be edited with precision. CRISPR is widely used in molecular biology research. It helps scientists explore how genes function and how DNA changes can affect living things.

experimental rnai

RNAi for Gene Silencing and Discovery

RNA interference (RNAi) is a gene-silencing process used to reduce gene expression. It can block transcription or trigger RNA degradation. Scientists first discovered this mechanism in plants in 1998 through Andrew Fire and Craig Mello. RNAi has since been found in many eukaryotes, including protozoa, flies, nematodes, insects, parasites, and mammals. Researchers use it as a practical tool to study gene function. It can show what a gene does without permanently changing the organism’s DNA. <br...

reporter genes

Reporter Genes in Cells and Plasmids

Reporter genes are protein-coding genes used to track gene activity in cells. They are often tagged to a gene of interest so scientists can see whether that gene is present or active. When the tagged genes are expressed together, reporter genes can produce visible signals such as fluorescence or luminescence. These signals help show the presence or absence of a gene of interest in an organism. They can also reveal the pattern of gene expression or the location of a DNA segment or protein...

in-situ hybridization

ISH Probes for DNA and RNA Detection

In situ hybridization (ISH) uses labeled probes to detect and localize specific DNA or RNA molecules in cells, tissues, or tissue sections. The probe is a complementary strand of DNA or RNA that binds to a matching nucleotide sequence in the sample. Since its first use in 1969 for nucleic acid studies, ISH has become an important tool in research and in clinical diagnosis. Several probe types can be used in ISH. These include single-stranded DNA probes, double-stranded DNA probes, antisense...

chromatin immunoprecipitation- chip

ChIP Methods for DNA-Protein Binding

Chromatin immunoprecipitation, or ChIP, is an antibody-based method for finding where proteins bind to DNA. It is used to identify DNA sites bound by transcription factors or histone proteins. ChIP also helps show which histone changes are present, including acetylation, phosphorylation, and methylation. ChIP is commonly divided into two forms: X-ChIP and N-ChIP. X-ChIP first cross-links proteins to DNA inside the cell, then breaks the DNA into pieces by sonication. The protein-DNA complexes...

synthetic biology

Synthetic Biology in Crops and Cells

Synthetic biology combines engineering, molecular biology, cell biology, and systems biology to redesign living systems. Scientists use it to remodel organisms from nature or to build new synthetic organisms. These tools can support protein or enzyme production, bioremediation, the production of useful macromolecules, and the addition of helpful traits to crops. One well-known example is golden rice. This genetically modified rice plant makes grains rich in β-carotene, which is a precursor of...

ribosome profiling

Ribosome Profiling for Translation Snapshot

Ribosome profiling is a deep sequencing method that gives a snapshot of active translation in a cell. It sequences the mRNAs protected by ribosomes. This shows which messages are being read to make proteins at a specific moment. The method has several uses in biology. It can track translation in a living organ or tissue type. It also helps measure new protein synthesis levels. Researchers use it to find translated open reading frames, which are stretches of RNA that can make protein. It can...

transgenic plants

Transgenic Plants for Better Crops

Transgenic plants are crops that have been changed with recombinant DNA technology, also called transgenesis. This method adds a foreign gene or removes a harmful one from an organism. The result is a genetically modified organism. The first transgenic plant was a tobacco plant made in 1983, and it was resistant to tobacco mosaic virus. Since then, transgenic plants have been developed for many uses in agriculture, horticulture, and ornamental plants. Some are designed to resist pests or...

gene therapy

Gene Therapy for Disease Treatment

Gene therapy is a treatment approach that changes gene activity to help address disease. It focuses on the genetic cause of a problem rather than only easing symptoms. In this way, it is used in disease intervention. One common strategy is to replace a faulty gene with a normal copy. Another strategy is to inactivate a gene that is causing harm. Gene therapy can also introduce a new gene to help cells work more normally.

epistasis analysis

Gene Interaction Maps in Epistasis

Gene interaction maps in epistasis show how different genes work together to shape a phenotype. In epistasis, the interaction of genes or alleles at different locations affects the final trait. This often happens when one gene masks or interferes with the expression of another gene. Epistasis is common when genes are part of the same biochemical pathway. In that case, the expression of one gene can depend on a gene product made earlier in the pathway. Genes that mask or inhibit other genes in...

genome-wide association studies-gwas

Using SNP Patterns to Link Disease Risk

Genome-wide association studies, or GWAS, look for common SNPs, or single nucleotide polymorphisms, that may be linked to disease. Researchers compare how often a SNP appears in people with a disease and in people without it. When a SNP is seen more often in the disease group, it is considered associated with that disease. GWAS uses chi-square analysis to test the chance that an allele is linked to the disease. This approach does not require scientists to first find the target gene behind the...

key terms and concepts

Learn how a test cross reveals whether a dominant organism is homozygous or heterozygous by crossing it with a recessive individual and checking offspring traits.

Test Cross in Genetic Inheritance | JoVE K12

molecular biology

JoVE Core Biología Molecular presenta los procesos moleculares de la célula a través de lecciones claras y concisas de animaciones audiovisuales. Además, en los vídeos de científicos en acción, se muestran aplicaciones de estos conceptos mediante experimentos reales en laboratorios especializados.

Test Cross in Genetic Inheritance

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