Name: using test crosses to identify genotypes
Uploaded: 2025-10-23T11:49:30.000Z
Duration: 1 min 39 s
Channel: JoVE

K12 Standards

Virginia  Standards of Learning

HIgh School

Life Science

LS.10

LS.10.c

Test Cross

- [내레이터] 검정 교배는 완두 식물에서보라색 꽃 색깔과 같은 지배적인 특성을 표현하는유기체의 유전자형을 결정하는데사용할 수 있는 기법입니다왜냐하면 유전자의 우성 버전 즉 대립 형질은항상 열성 대립 형질을 통해 표현될 것이기 때문에두 개의 우성 대립 형질은한 개의 우성 대립형질즉 이질 유전형을 가진 유기체들과똑같이 보일 것입니다알 수 없는 유전자형의 보라색 꽃이 피는 완두콩 식물은열성 표현형 하얀 꽃을 가진완두콩 식물로 건너갈 수 있습니다따라서 동종접합 열성의 유전자형이있는 것으로 알려져 있는데요, 소문자 p, 소문자 p이죠한 시나리오에서, 검정 교배의 모든 자손이지배적인 표현형을 표시하는 경우알 수 없는 모체는 보라색 꽃의동종접합 우성이어야 합니다모든 자손은 열성 부모로부터 한 개의 열성 대립형질을 받고다른 부모로부터 한 개의 우세한대립형질을 받는 이형접합체입니다하지만, 자손이 우성 표현형을 나타내는균의 수와 열성 표현형을 보이는유기체를 포함한다면알려지지 않은 모체는 이형접합자여야 합니다모든 자손은 열성 부모로부터열성 대립형질을 받습니다자손의 절반이 이형접합체 부모로부터우성 대립형질을 받고우성 표현형을 보이는 반면나머지 절반은 이형접합체 부모로부터열성 대립형질을 받아열성 표현형을 보여줍니다

미코, 일로나. 2008. "테스트 크로스." 자연 교육 1 (1) : 136. [<a href="https://www.nature.com/scitable/topicpage/test-crosses-585">출처</a>]

리드, 제임스 B., 존 J. 로스. 2011. "멘델의 유전자 : 완전한 분자 특성화를 향하여" Genetics 189 (1) : 3–10. [<a href="https://doi.org/10.1534/genetics.111.132118">출처</a>]

검정교배

대립유전자(allele)는 같은 유전자(gene)의 다른 형태입니다. 인간과 다른 이배체(diploid) 유기체들은 모든 유전자당 대립유전자 두 개, 즉 각 부모에게서 한 개씩 물려받습니다.
 
 대립유전자는 자신의 효과가 같은 유전자 위치에 있는 다른 대립유전자에게 가려지면 잠성(recessive)입니다 (주: dominant를 우성이라 부르고 recessive를 열성이라 부르는 경우가 아직 많지만, 과학적으로 현성/잠성이란 단어가 현상을 더 정확하게 정의하는 단어입니다. 게다가 우성/열성이란 단어는 차별로 이어질 수 있기 때문에 현성/잠성이란 표현으로 개선해야 합니다). 예를 들어 완두는 보라색 또는 흰색 꽃을 가질 수 있습니다. 이 경우, 보라색 꽃에 대한 대립유전자 사본 1개만 있으면 흰색 꽃에 대한 대립유전자가 있더라도 식물은 보라색 꽃을 피우기 때문에 흰색 꽃은 잠성입니다.
 
 만약 유기체가 알려진 잠성 형질(trait)을 보인다면, 유기체의 유전자형(genotype), 즉 유전된 대립유전자 쌍을 결정하는 것은 간단합니다. 오직 유전자형 pp(잠성 대립유전자 2개)만이 흰색 꽃을 생산합니다.
 
 보라색 꽃을 가진 완두와 같은 현성(dominant) 형질을 가진 유기체의 유전자형을 결정하는 것은 그렇게 간단하지 않습니다. 두 유전자형 PP와 Pp가 보라색 꽃을 생산합니다.
 
 과학자들은 단순한 현성 형질을 보이는 유기체의 유전자형을 결정하기 위해 검정교배(test cross)를 사용합니다. 검정교배는 해당 유기체를 그 유기체가 가진 현성 형질의 잠성 대상과 교배하는 것을 뜻합니다.
 
 보라색 꽃을 가진 완두를 위한 검정교배에선 보라색 꽃 완두가 흰색 꽃을 가진 완두(pp)와 함께 교배됩니다. 여기서 얻은 자손의 꽃 색깔은 보라색 꽃을 가진 부모가 동형접합적(homozygous; PP)인지 또는 이형접합적(heterozygous; Pp)인지를 나타냅니다.
 
 만약 보라색 꽃을 가진 완두가 동형접합적이면, 모든 자손은 해당 완두의 현성 대립유전자 P 중 하나와 다른 부모의 잠성 대립유전자 p 중 하나를 물려받을 것입니다. 현성 대립유전자는 잠성 대립유전자를 가리기 때문에, 모든 자손은 현성 형질인 보라색 꽃을 가질 것입니다.
 
 그러나 만약 보라색 꽃을 가진 완두가 이형접합적이라면, 약 50%의 자손이 해당 완두에게서 잠성 대립유전자 p를, 다른 부모에게서 또 잠성 대립유전자 p를 물려받을 것입니다. 따라서 이 교배에서 나온 약 절반의 자손은 흰색 꽃을 가질 것입니다. 검정교배는 이러한 방식으로 알려지지 않은 부모 유전자형을 밝힐 수 있습니다.

대립유전자는 동일한 유전자의 다른 형태입니다. 인간과 다른 이배체 유기체는 각 부모로부터 하나씩 모든 유전자의 두 개의 대립유전자를 물려받습니다.

대립유전자는 ...

Education

교육

JoVE Core

Biology

생물학

Genetics

유전학

Classical and Modern Genetics

고전 유전학과 현대 유전학

KEY TERMS AND CONCEPTS

주요 용어 및 개념

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 allele is enough to make a plant purple, even if it also carries the white allele.

When a trait is recessive, the genotype is easy to determine. For white pea flowers, only one genotype produces the trait: pp, with two recessive alleles. The problem is different for dominant traits, such as purple flowers. Two genotypes, PP and Pp, can both produce purple flowers.

Scientists use a test cross to solve that problem. In this method, the organism with the dominant trait is bred with an organism that shows the recessive version of the same trait. For a purple-flowered pea plant, the cross is made with a white-flowered pea plant with the pp genotype. The offspring then show whether the purple parent is homozygous, meaning PP, or heterozygous, meaning Pp.

The offspring pattern gives the answer. If the purple plant is homozygous, every offspring inherits one dominant P allele and one recessive p allele, so they all have purple flowers. If the purple plant is heterozygous, about half of the offspring inherit the recessive p allele from that parent and become white. In this way, test crosses reveal unknown parental genotypes.

Using Test Crosses to Identify Genotypes

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 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

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...

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...

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...

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 a test cross uses a recessive partner to reveal whether a dominant trait is homozygous or heterozygous in pea plants.

Using Test Crosses to Identify Genotypes | JoVE K12

JoVE Core series brings biology to life through over 300 concise and easy-to-understand animated video lessons that explain key concepts in biology, plus more than 150 scientist-in-action videos that show actual research experiments conducted in today’s laboratories.

biology

JoVE Core 시리즈는 생물학의 주요 개념을 설명하는 300개가 넘는 간결하고 이해하기 쉬운 애니메이션 비디오 강의와 오늘날 실험실에서 수행된 실제 연구 실험을 보여주는 150개가 넘는 과학자 활동 비디오를 통해 생물학에 활기를 불어 넣습니다.

Next Generation Science Standards

High School

heredity-inheritance-and-variation-of-traits

Heredity: Inheritance and Variation of Traits

HS-LS3-1

new-york-state-science-learning-standards

New York State Science Learning Standards

Inheritance and Variation of Traits

HS-LS3-1.

Georgia Standards of Excellence

9-12

SB3.a

Florida Department of Education

SC.912.L.16

SC.912.L.16.1

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Using Test Crosses to Identify Genotypes

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