Name: mendel’s dihybrid cross and trait ratios
Uploaded: 2026-08-26T08:20:47.748Z
Duration: 2 min 36 s
Channel: JoVE

K12 Standards

Virginia  Standards of Learning

HIgh School

Life Science

LS.10

LS.10.c

Law of Independent Assortment

Durch seine ersten Experimente stellte Gregor Mendel fest, dass es Einheiten gibt, Gene, die daf&#xFC;r verantwortlich sind, Eigenschaften von Elternteil zu Nachkommen zu &#xFC;bertragen.
 Jeder Organismus hat zwei Kopien jedes Gens, die Allelen genannt werden, wobei jeweils eine Kopie von jeweils einem Elternteil vererbt wurde.
 In seinem n&#xE4;chsten Experiment benutzte Mendel dihybride Kreuzungen von Erbsenpflanzen, die sich in zwei Eigenschaften unterschieden, zum Beispiel L&#xE4;nge und Bl&#xFC;tenfarbe, um herauszufinden, ob die Vererbung einer Eigenschaft die Vererbung einer anderen beeinflusst.
 Wenn die Allelen f&#xFC;r die beiden Eigenschaften in einer dihybriden Kreuzung von einer Elterngeneration als Einheit vererbt w&#xFC;rden, wenn sich die F1-Generation fortpflanzt, dann w&#xFC;rden die F2-Nachkommen immer entweder beide dominanten oder beide rezessiven Ph&#xE4;notypen aufweisen, aber nie eine Kombination aus beiden.
 Als Mendel die dihybriden F1-Erbsenpflanzen kreuzte, stellte er fest, dass bei 16 F2-Nachkommen etwa neun beide dominanten Ph&#xE4;notypen aufwiesen, drei nur einen dominanten und einen rezessiven Genotyp aufwiesen, drei weitere die umgekehrte Kombination von rezessiven und dominanten Ph&#xE4;notypen aufwiesen, und einer beide rezessiven Ph&#xE4;notyp aufwies.
 Das Verh&#xE4;ltnis von dominanten zu rezessiven Ph&#xE4;notypen f&#xFC;r jede gesonderte Eigenschaft ist noch immer drei zu eins in einer F2-Generation.
 Alle vier Kombinationen des Ph&#xE4;notyps konnten nur auftreten, wenn die dominanten und rezessiven Allelen f&#xFC;r L&#xE4;nge nicht mit den dominanten und rezessiven Allelen f&#xFC;r Bl&#xFC;tenfarbe verbunden waren.
 Diese Beobachtungen schafften die Grundlage f&#xFC;r Mendels Unabh&#xE4;ngigkeitsregel, die besagt, dass Allelen f&#xFC;r verschiedene Gene sich unabh&#xE4;ngig voneinander in Keimzellen verteilen.
 Das neun, drei, drei, eins Ph&#xE4;notyp-Verh&#xE4;ltnis deutet darauf hin, dass jeder dihybride Elternteil mit gleicher Wahrscheinlichkeit alle wahrscheinliche Kombinationen von dominanten und rezessiven Allelen vererbt.
 Lang, mit lilanen Bl&#xFC;ten, lang, mit wei&#xDF;en Bl&#xFC;ten, kurz, mit lilanen Bl&#xFC;ten, oder kurz mit wei&#xDF;en Bl&#xFC;ten.

Jäger, Neil. "Meiotische Rekombination: das Wesen der Vererbung." Perspektiven des Cold Spring Harbor in der Biologie 7, Nr. 12 (2015): a016618. [<a href="https://dx.doi.org/10.1101%2Fcshperspect.a016618">Quelltext</a>]

die unabhängigkeitsregel

W&#xE4;hrend die Mendelsche Spaltungsregel besagt, dass die beiden Allele f&#xFC;r ein Gen in verschiedene Keimzellen getrennt sind, bleibt die Frage bestehen, wie verschiedene Gene vererbt werden. Wird zum Beispiel das Gen f&#xFC;r gro&#xDF;e Pflanzen zusammen mit dem Gen f&#xFC;r gr&#xFC;ne Erbsen vererbt? Mendel pr&#xFC;fte diese Frage, indem er mit einer dihybriden Kreuzung experimentierte. Das sind Kreuzungen, bei der beide Eltern f&#xFC;r zwei verschiedene Merkmale homozygot sind, was zu einer F1Generation f&#xFC;hrt, die f&#xFC;r beide Merkmale heterozygot ist.
 
 Schauen wir uns zwei homozygote Pflanzen an. Eine tr&#xE4;gt runde, gelbe Erbsen (Genotyp YYRR), w&#xE4;hrend die andere runzlige, gr&#xFC;ne Erbsen (Yyrr) tr&#xE4;gt. In der F1-Generation stellte Mendel fest, dass alle Pflanzen beide dominante Merkmale (gelb und rund; YyRr) aufweisen. In der F2 -Generation hatten die Pflanzen jedoch verschiedene Kombinationen der Merkmale, die in einem vorhersehbaren Verh&#xE4;ltnis auftraten. Von 16 Pflanzen waren 9 gelb und rund, 3 gelb und runzelig, 3 gr&#xFC;n und rund und eine gr&#xFC;n und runzelig. Aufgrund dieses Ergebnisses vermutete Mendel, dass die Aufnahme des gr&#xFC;nen Allels in eine Keimzelle keinen Einfluss darauf hat, ob diese Keimzelle das runde oder das runzelige Allel erh&#xE4;lt. Jede Kombination hat also die gleiche Wahrscheinlichkeit. Mendels Unabh&#xE4;ngigkeitsregel besagt, dass sich die Gene hinsichtlich der Aufteilung in die Gameten nicht gegenseitig beeinflussen.
 
 Heute wissen die Wissenschaftler, dass das Unabh&#xE4;ngigkeitsregel auftritt, da sich die Chromosomen w&#xE4;hrend der Meiose I entlang der Metaphasenplatte zuf&#xE4;llig zusammenf&#xFC;gen. Als Folge davon werden Gene von verschiedenen Chromosomen unabh&#xE4;ngig voneinander aufgeteilt. Dies bedeutet auch, dass zwei auf demselben Chromosom liegende Gene die Unabh&#xE4;ngigkeitsregel nicht erf&#xFC;llen, insbesondere wenn sie sehr nahe beieinander liegen, da sie fast immer gemeinsam vererbt werden. Dieses Ph&#xE4;nomen wird als Genkopplung auf der Chromosomenebene beschrieben. Gekoppelte Gene ergeben nicht das 9:3:3:1 Verh&#xE4;ltnis in der F2-Generation nach einer dihybriden Kreuzung.

Die Unabhängigkeitsregel

While Mendel&#x2019;s Law of Segregation states that the two alleles for one gene are separated into different gametes, a different question of how ...

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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 generation showed a predictable pattern. For every 16 plants, 9 were yellow and round, 3 were yellow and wrinkled, 3 were green and round, and 1 was green and wrinkled. From this result, Mendel proposed that having a green allele in a gamete did not affect whether that gamete received the round or wrinkled allele.

This idea became Mendel’s Law of Independent Assortment. It means that genes do not influence one another when they sort into gametes. Scientists now explain this by the random pairing of chromosomes during meiosis I at the metaphase plate. Genes on different chromosomes therefore sort independently, while genes on the same chromosome can be inherited together as linked genes and may not show the 9:3:3:1 F2 ratio.

Mendel’s Dihybrid Cross and Trait Ratios

genetic lingo

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,...

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 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...

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...

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...

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...

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...

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,...

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%...

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...

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...

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.

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-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...

key terms and concepts

Learn how Mendel’s dihybrid cross revealed the 9:3:3:1 F2 ratio, independent assortment, and why linked genes on the same chromosome can stay together.

Mendel’s Dihybrid Cross and Trait Ratios | JoVE K12

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heredity-inheritance-and-variation-of-traits

Heredity: Inheritance and Variation of Traits

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Inheritance and Variation of Traits

HS-LS3-1.

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SC.912.L.16

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LS.10.b

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Mendel’s Dihybrid Cross and Trait Ratios

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