Name: genotype, phenotype, and inheritance
Uploaded: 2019-03-11T09:21:16.000Z
Duration: 1 min 11 s
Channel: JoVE

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Genetic Lingo

Allele to różne formy tego samego genu. Jeden jest otrzymywany od każdego rodzica, w wyniku czego powstaje organizm diploidalny. Dwa allele w tym samym locus dla każdego zaangażowanego genu.

Każda para jest znana jako genotyp określonego genu oraz fizyczna i obserwowalna ekspresja, fenotyp, taki jak kolor oczu, jest determinowany przez odziedziczoną kombinację.

W tym przypadku jeden z genów zawiera dwa allele dla potencjalnych kolorów brązowego i niebieskiego. Jeśli obie formy są identyczne, genotyp nazywa się homozygotycznym.

Natomiast jeśli para się różni, genotyp jest heterozygotyczny. Co ciekawe, ten sam fenotyp, taki jak brązowe oczy, może być wyrażany z różnych genotypów. Dzieje się tak, ponieważ allel dominujący, brązowy pokazany jako wielka litera, jest wyrażony nad allelem recesywnym, niebieski jest zapisany jako mała litera. Tak więc jedynym sposobem, w jaki allel recesywny może być wyrażony, jest to, że obie kopie są recesywne.

Fay, Davida i Andy'ego Spencerów. Mutacje dominujące. WormBook, 2006. [<a href="https://www.ncbi.nlm.nih.gov/books/NBK19699/" target="__blank">Źródło</a>].

genetyczny żargon

<h4>Przegląd</h4>

Organizm jest diploidalny, jeśli dziedziczy dwa warianty lub allele każdego genu, po jednym od każdego z rodziców. Te dwa allele stanowią genotyp danego genu. Terminu genotyp używa się również w odniesieniu do pełnego zestawu genów organizmu. Organizm diploidalny z dwoma identycznymi allelami ma genotyp homozygotyczny, podczas gdy dwa różne allele wskazują na genotyp heterozygotyczny. Obserwowalne cechy wynikające z genotypów nazywane są fenotypami, na które mogą wpływać również czynniki środowiskowe. Allel jest dominujący, jeśli do ujawnienia powiązanego fenotypu potrzebna jest tylko jedna kopia, i recesywny, jeśli do ekspresji fenotypowej potrzebne są dwie kopie.

<h4>Allele mogą wpływać na fenotypy</h4>

Organizmy diploidalne, w tym ludzie, większość innych zwierząt i wiele roślin, mają zduplikowany zestaw chromosomów w komórkach somatycznych (niepłciowych). Te duplikaty chromosomów są homologiczne, mają podobną długość, pozycje centromerów i lokalizacje genów. Organizmy diploidalne dziedziczą dwie wersje każdego genu, po jednej od każdego z rodziców. Te dwa warianty genów lub allele znajdują się w tym samym względnym locus lub pozycji na dwóch homologicznych chromosomach. Każdy chromosom zawiera wiele loci genetycznych i często istnieje kilka możliwych alleli danego genu.

Dwa allele odziedziczone przez organizm diploidalny stanowią jego genotyp w miejscu. Termin genotyp odnosi się również do całkowitego zestawu genów organizmu. Różne genotypy mogą skutkować odrębnymi fenotypami lub obserwowalnymi cechami (np. Kolorem oczu). Fenotypy powstają w wyniku genotypów, chociaż wiele genotypów może powodować ten sam fenotyp. Na fenotypy często wpływają również czynniki środowiskowe.

<h4>Genotyp może składać się z dwóch identycznych lub odrębnych alleli</h4>

W przypadku danego genu dwa odziedziczone allele mogą mieć identyczne lub różne sekwencje nukleotydowe. Organizm z dwoma identycznymi allelami ma genotyp homozygotyczny (lub jest homozygotą). Organizm z dwoma różnymi allelami ma genotyp heterozygotyczny (tj. jest heterozygotą). Jeśli dwa allele są różne (genotyp heterozygotyczny), ale tylko jeden wpływa na fenotyp, allel wpływający na fenotyp jest dominujący. Drugi allel, który nie wpływa na fenotyp, jest recesywny.

Pierwotnie sądzono, że kolor oczu jest determinowany przez pojedynczy gen, dlatego często używa się go do zilustrowania dominacji genetycznej (oczy brązowe) i recesywności (oczy niebieskie). Naukowcy odkryli jednak co najmniej osiem genów regulujących kolor oczu. Chociaż gen OCA2 jest odpowiedzialny za prawie trzy czwarte zmienności spektrum niebiesko-brązowego koloru oczu, inne geny czasami modyfikują lub zastępują te efekty. Niemniej jednak kolor oczu może być użytecznym przykładem ilustrującym allele dominujące i recesywne.

Poniżej używamy uproszczonego przykładu koloru oczu, aby zilustrować związek między genotypem a fenotypem. Allel dla oczu brązowych jest oznaczony jako B, a allel dla oczu niebieskich to b. Heterozygota będzie miała genotyp Bb w wyniku otrzymania allelu dominującego od jednego z rodziców i allelu recesywnego od drugiego. Osoba ta miałaby brązowe oczy, dominujący fenotyp. Allel dominujący (B) zastępuje lub “ukrywa“ instrukcje przed allelem recesywnym odpowiedzialnym za niebieskie oczy. Zatem osoba o niebieskich oczach będzie musiała mieć genotyp bb, podczas gdy osoba o brązowych oczach może mieć genotyp BB lub Bb.

<h4>Dominujące i recesywne wzorce dziedziczenia chorób są powiązane z ryzykiem choroby</h4>

Chociaż większość cech jest kontrolowana przez wiele genów, a nie przez pojedynczy gen przyczynowy, zasady te mogą być przydatne do przewidywania prawdopodobieństwa wystąpienia ważnych wyników. Na przykład choroba Huntingtona (HD) jest postępującą chorobą neurodegeneracyjną, która powoduje niekontrolowane ruchy oraz zaburzenia poznawcze i emocjonalne. HD uważa się za chorobę jednogenową, ponieważ jest spowodowana mutacją w jednym genie (HTT), chociaż inne geny modyfikują początek i postęp choroby. HD jest spowodowana dominującą mutacją, co oznacza, że pojedynczy zmutowany allel prowadzi do ekspresji choroby. Jeśli rodzic ma prawidłowy i zmutowany wariant genu, potomstwo ma 50% szans na otrzymanie zmutowanego allelu i rozwój choroby. HD zwykle nie objawia się aż do połowy lub późnego wieku. Tak więc, chociaż rzeczywistość jest nieprzyjemna, osoba, której rodzic jest dotknięty chorobą, może przejść badania genetyczne w celu ustalenia, czy ma allel przyczynowy, co z kolei umożliwi planowanie rodziny.

Genetyczny żargon

Przegląd

Organizm jest diploidalny, jeśli dziedziczy dwa warianty lub allele każdego genu, po jednym od każdego rodzica. Te dwa allele stanowią genotyp ...

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Kluczowe terminy i pojęcia

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.

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LS.10.b

Overview

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Punnett Squares

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Dihybrid Crosses

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Law of Segregation

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Test Cross

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Genotype, Phenotype, and Inheritance

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