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

対立遺伝子は同一遺伝子の異なる形態です。各親から1つずつ、二倍体生物、関与するすべての遺伝子について 二倍体生物に関与するすべての遺伝子について 同じ遺伝子座に2つの対立遺伝子が生じます。各ペアは、特定の遺伝子の遺伝子型として知られており、遺伝子型として知られており、肉眼的色などの表現型は、遺伝的な組み合わせによって決定されます。この場合、遺伝子のうちの1つには、褐色と青色の2色の対立遺伝子が含まれています。両方の型が同一の場合、その遺伝子型はホモ接合型と呼ばれます。対が異なる場合、その遺伝子型はヘテロ接合型です。興味深いことに、茶色の目のような同じ表現型は、異なる遺伝子型から発現することがあります。これは、大文字で示されている 茶色の優性対立遺伝子が、小文字で書かれている劣性の対立遺伝子である 青の上に表現されているためです。したがって、劣性対立遺伝子を発現させることができる唯一の方法は、両方のコピーが劣性である場合です。

フェイ、デビッド、アンディ・スペンサー。優性突然変異。ワームブック、2006年。[<a href="https://www.ncbi.nlm.nih.gov/books/NBK19699/" target="__blank">ソース</a>]。

遺伝学的用語

<h4>概説</h4
 
 生物は、それぞれの親から2つの遺伝子の変異体（対立遺伝子）を受け継ぐと二倍体となります。この2つの対立遺伝子が、ある遺伝子の遺伝子型を構成します。また、遺伝子型とは、生物の完全な遺伝子セットを指す言葉でもあります。2つの同じ対立遺伝子を持つ二倍体の生物はホモ接合の遺伝子型であり、2つの異なる対立遺伝子を持つ生物はヘテロ接合の遺伝子型を示します。遺伝子型から生じる観察可能な形質を「表現型」といい、環境因子の影響を受けることもあります。表現型の発現に1つのコピーしか必要としないものを顕性（優性）、2つのコピーが必要なものを潜性（劣性）といいます。
 
 <h4>表現型に影響を与える対立遺伝子</h4>。
 
 ヒトをはじめとするほとんどの動物や多くの植物を含む二倍体の生物は、体細胞（非性細胞）の染色体が重複しています。これらの染色体は、長さ、セントロメアの位置、遺伝子の位置などが似ているという相同性を持っています。二倍体の生物は、それぞれの親から1つずつ、2つのバージョンの遺伝子を受け継ぎます。これらの2つの遺伝子の変異体（対立遺伝子）は、相同性のある2つの染色体上の同じ相対的な遺伝子座（位置）に存在します。それぞれの染色体には多くの遺伝子座があり、1つの遺伝子に対して複数の対立遺伝子が存在することがあります。
 
 二倍体の生物が受け継ぐ2つの対立遺伝子は、その遺伝子座における遺伝子型を構成します。 遺伝子型とは、生物の全遺伝子の集合体を意味します。遺伝子型が異なると、表現型、つまり観察可能な特性（例えば、目の色）が異なります。表現型は遺伝子型の結果として現れるものですが、複数の遺伝子型が同じ表現型を引き起こすこともあります。表現型は、環境要因によっても影響を受けることがあります。
 
 <h4>遺伝子型は、2つの同じまたは異なる対立遺伝子からなります</h4>。
 
 ある遺伝子の2つの対立遺伝子は、同一のヌクレオチド配列を持つ場合と、異なるヌクレオチド配列を持つ場合があります。2つの同一の対立遺伝子を持つ生物は、ホモ接合の遺伝子型を持ちます。異なる2つの対立遺伝子を有する生物は、ヘテロ接合の遺伝子型を有します（すなわち、ヘテロ接合体である）。2つの対立遺伝子が異なっていても（ヘテロ接合の遺伝子型）、一方だけが表現型に影響を与える場合、表現型に影響を与える対立遺伝子が顕性です。表現型に影響を与えないもう一方の対立遺伝子は潜性です。
 
 もともと、目の色は1つの遺伝子で決まると考えられていたため、遺伝子の顕性（茶目）や潜性（青目）を説明するのによく使われます。しかし、科学者たちは、目の色を調節する少なくとも8つの遺伝子を発見しています。青と茶色の目の色のバリエーションの約4分の3はOCA2遺伝子が担っていますが、他の遺伝子がその効果を修正したり上書きしたりすることもあります。しかし、目の色は、顕性対立遺伝子と潜性対立遺伝子を説明するための有用な例となります。
 
 以下では、遺伝子型と表現型の関係を説明するために、単純化した目の色の例を使用します。茶色い目の対立遺伝子をB、青い目の対立遺伝子をbと表記します。ヘテロ接合体は、片方の親から顕性対立遺伝子を、もう片方の親から潜性対立遺伝子を受け取った結果、遺伝子型がBbとなります。この個体は、顕性表現型である茶色の目を持つことになります。顕性対立遺伝子（B）は、青い目の潜性対立遺伝子からの指示を無効にしたり、隠したりします。したがって、青い目の人は必ず遺伝子型bbを持つことになりますが、茶色の目の人は遺伝子型BBまたはBbをもつ可能性があります。
 
 <h4>顕性遺伝と潜性遺伝のパターンは病気のリスクと関係があります</h4>。
 
 多くの形質は単一の原因遺伝子ではなく、複数の遺伝子によって制御されていますが、これらの原理は重要な結果の確率を予測するのに役立ちます。例えば、ハンチントン病（HD）は、進行性の神経変性疾患で、制御不能な動きや認知・感情障害を引き起こします。HDは、単一の遺伝子（HTT）の変異によって引き起こされるため、単一遺伝子疾患と考えられていますが、他の遺伝子が発症や進行を修飾することもあります。HDは、顕性突然変異によって引き起こされます。つまり、1つの変異した対立遺伝子が疾患の発現につながります。親が正常な遺伝子と変異した遺伝子を持っている場合、子孫は50％の確率で変異した対立遺伝子を受け継ぎ、病気を発症することになります。また、HDは通常、中年から晩年になってから発症します。現実は厳しいですが、親がHDに罹患している人は、遺伝子検査を受けて原因遺伝子を持っているかどうかを確認し、家族計画に反映させることができます。

概要

生物は、各遺伝子の2つの変異体または対立遺伝子を、各親から1つずつ受け継ぐ場合、二倍体です。これらの2つの対立遺伝子は遺伝子型を構成します...

Education

JoVE Core

Biology

生物学

Genetics

遺伝学

Classical and Modern Genetics

古典遺伝学と現代遺伝学

KEY TERMS AND CONCEPTS

主要用語と概念

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...

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 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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biology

JoVE Core シリーズは、生物学の重要な概念を説明する 300 を超える簡潔でわかりやすいアニメーション ビデオ レッスンに加え、今日の研究室で行われる実際の研究実験を示す 150 以上の科学者の活動ビデオを通じて、生物学に命を吹き込みます。

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.

myJoVE Corporation

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LS.10.a

What is Meiosis?

Meiosis is the process by which diploid cells divide to produce haploid daughter cells. In humans, each diploid cell contains 46 chromosomes, half from ...

Meiosis I

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Meiosis II

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Nondisjunction

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The student will investigate and understand that organisms reproduce and transmit genetic information to new generations. Key ideas include the role of meiosis is to transfer traits to the next generation; and

LS.10.b

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 ...

Punnett Squares

Overview

A Punnett square displays the possible genotypes offspring can inherit from two parental genotypes. If a trait&#x2019;s inheritance pattern ...

Monohybrid Crosses

Overview

In the 1850s and 1860s, Gregor Mendel investigated inheritance by performing monohybrid crosses in pea plants. He crossed two plants that were ...

Dihybrid Crosses

Overview

To determine whether traits are inherited together or separately, Gregor Mendel crossed pea plants that differed in two traits. These parental ...

Law of Segregation

When crossing pea plants, Mendel noticed that one of the parental traits would sometimes disappear in the first generation of offspring, called the F1 ...

Law of Independent Assortment

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 ...

Test Cross

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 ...

Pedigree Analysis

Overview

A pedigree is a diagram displaying a family&#x2019;s history of a trait. Analyzing pedigrees can reveal (1) whether a trait is dominant or ...

X-linked Traits

In most mammalian species, females have two X sex chromosomes and males have an X and Y. As a result, mutations on the X chromosome in females may be ...

Sex-linked Disorders

Like autosomes, sex chromosomes contain a variety of genes necessary for normal body function. When a mutation in one of these genes results in biological ...

Nature and Nurture

Many human characteristics, like height, are shaped by both nature&mdash;in other words, by our genes&mdash;and by nurture, or our environment. For ...

The student will investigate and understand that organisms reproduce and transmit genetic information to new generations. Key ideas include Punnett squares are mathematical models used to predict the probability of traits in offspring.

Genotype, Phenotype, and Inheritance

Description

Transcript

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