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

- [Narratore] Il test cross &#xE8; una tecnica

che pu&#xF2; essere usata per
determinare il genotipo

di un organismo, che
esprime un tratto dominante,

come il colore del fiore
viola nelle piante di pisello.

Poich&#xE8; la versione dominante,
o allele di un gene,

sar&#xE0; sempre espresso a
scapito dell&#x27;allele recessivo,

organismi con il genotipo
omozigote-dominante,

due alleli dominanti, appariranno uguali

agli organismi con il
genotipo eterozigote,

un allele dominante.

Una pianta di piselli a fiore
viola di genotipo sconosciuto,

pu&#xF2; essere incrociata con
una pianta di piselli che ha

il fenotipo recessivo, fiori bianchi.

E quella &#xE8; noto avere

il genotipo omozigote-recessivo,
p piccolo, p piccolo.

In un caso, se tutti i figli

dal test cross,

mostrano il fenotipo dominante,
il genitore sconosciuto

deve essere omozigote-dominante
per i fiori viola.

Tutti i figli sono eterozigoti,

ricevono un allele recessivo
dal genitore recessivo,

e un allele dominante dell&#x27;altro genitore.

Tuttavia, se la discendenza
include numeri uguali

di organismi, che mostrano
il fenotipo dominante,

e organismi che mostrano
il fenotipo recessivo,

il genitore sconosciuto
deve essere eterozigote.

Tutti i figli ricevono, di
nuovo, il loro allele recessivo

dal genitore recessivo.

La met&#xE0; della prole ha
ricevuto un allele dominante

dal genitore eterozigote,

e mostra il fenotipo dominante,

mentre l&#x27;altra met&#xE0; ha
ricevuto una seconda copia

dell&#x27;allele recessivo
dal genitore eterozigote,

e mostra il fenotipo recessivo.

Miko, Ilona. 2008. "Incroci di prova". Educazione alla natura 1 (1): 136. [<a href="https://www.nature.com/scitable/topicpage/test-crosses-585">Fonte</a>]

Reid, James B. e John J. Ross. 2011. "I geni di Mendel: verso una caratterizzazione molecolare completa" Genetica 189 (1): 3–10. [<a href="https://doi.org/10.1534/genetics.111.132118">Fonte</a>]

reincrocio

Test Cross

Gli alleli sono forme diverse dello stesso gene. Gli esseri umani e altri organismi diploidi ereditano due alleli di ogni gene, uno da ogni genitore.
Un allele &#xE8; recessivo se i suoi effetti sono mascherati da un altro allele nella stessa posizione genica. Ad esempio, le piante di pisone possono avere fiori viola o bianchi. In questo caso, i fiori bianchi sono recessivi poich&#xE9; una singola copia dell&#x27;allele per i fiori viola si tradurr&#xE0; in una pianta con fiori viola, anche se hanno anche l&#x27;allele per i fiori bianchi.
Se un organismo mostra un tratto recessivo noto, determinare il genotipo dell&#x27;organismo, la sua coppia di alleli ereditati, &#xE8; semplice. Solo un genotipo,
pp
(due alleli recessivi), produce fiori bianchi.
Per un organismo con un tratto dominante, come una pianta di piselli con fiori viola, determinare il genotipo non &#xE8; cos&#xEC; semplice. Due genotipi,
PP
e
Pp
, producono fiori viola.
Gli scienziati usano incroci di prova per determinare i genotipi degli organismi che presentano semplici tratti dominanti. Un incrocio di prova coinvolge l&#x27;allevamento, o attraversamento, dell&#x27;organismo in questione con uno che mostra la controparte recessiva del suo tratto dominante.
In un incrocio di prova per una pianta di pisoni con fiori viola, la pianta viene allevata con una pianta di pisoni che ha fiori bianchi (
genotipo pp).
Il colore del fiore della prole risultante rivela se il genitore con fiori viola &#xE8; omozigote (
PP
) o etetozigote (
Pp
).
Se la pianta &#xE8; omozigote, tutta la prole erediter&#xE0; uno dei suoi
p
alleli dominanti e uno degli alleli p recessivi dell&#x27;altro genitore. Poich&#xE9; gli alleli dominanti mascherare alleli recessivi, tutti i figli avranno fiori viola, il tratto dominante.
Se la pianta &#xE8; eterozigote, tuttavia, circa il 50% della prole erediter&#xE0; il suo
allele recessivo p,
insieme a un altro allele recessivo dall&#x27;altro genitore. Pertanto, circa la met&#xE0; della prole da questo incrocio avr&#xE0; fiori bianchi. In questo modo, le croci di prova possono rivelare genotipi parentali sconosciuti.

Reincrocio

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

Didattica

JoVE Core

Molecular Biology

Biologia Molecolare

Unit 2

Unità 2

Analyzing Gene Expression and Function

Analisi dell'espressione e della funzione genica

KEY TERMS AND CONCEPTS

TERMINI E CONCETTI CHIAVE

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

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Bacterial Transformation in the Lab

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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...

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Cloning an Organism by Reproduction

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crispr

CRISPR Gene Editing Basics

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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

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ribosome profiling

Ribosome Profiling for Translation Snapshot

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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

Le video animazioni di JoVE Core Molecular Biology, organizzate in video lezioni, illustrano i processi molecolari cellulari in maniera chiara e concisa. Inoltre, nei video di "scienziati in azione", i concetti scientifici vengono applicati e dimostrati da ricercatori attraverso esperimenti in laboratorio.

Test Cross in Genetic Inheritance

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