Allele definition simple

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Allele definition simple

An allele is a form of a gene at a particular position locus on a chromosome. Typical plants and animals have two sets of chromosomes, one set inherited from each parent. Since such organisms have two sets of chromosomes, they have except on the sex chromosomes two alleles at each gene locus.

If the two alleles are identical, the individual is called a homozygote and is said to be homozygous. If instead the two alleles are different, the individual is a heterozygote and is heterozygous.


That is, the phenotype produced by the two alleles in heterozygous combination is identical to that produced by one of the two homozygous genotypes. The allele that masks the other is said to be dominant to the latter, and the alternative allele is said to be recessive to the former.

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This idea originates in the work of Gregor Mendelthe founder of genetics. The inheritance of alleles, and their dominance, can be represented in a Punnett square.

An example is the gene for blossom colour in many species of flower.

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A single gene controls the colour of the petalsbut there may be several different versions or alleles of the gene. In this example, parents have the genotype Bb capital letters show dominant alleles and lower-case letters to show recessive alleles.

If B capital is found in their genotype, the flower will be red. Therefore, the only time a flower is not red is when the genotype is bb there are no capital 'B's. The phenotype of the flower will always be red if a dominant B is in the genotype. The pattern of inheritance of recessive genes is quite simple. If they are heterozygous with a dominant allele, the appearance phenotype is the same as a dominant homozygote.

Only if both alleles are recessive does the recessive allele show in the phenotype b. This is when the dominant allele is not completely dominant over the recessive allele. This means both the alleles have a degree of phenotypic expression in the hybrids. In this case the functional product formed is a little different or is intermediate between the product produced by to the dominant allele and the recessive allele.

For example: Mirabilis jalapa. The heterozygote of this plant produces flowers in the F1 generation of the colour pink in contrast to the red dominant and white recessive homozygotes. Genes on the sex chromosomes are said to be sex linked. In the XY sex determination system of mammalsthe X chromosomes carry a full set of genes, but the Y chromosomes carry few genes.

Alleles or genes which are not sex-linked are called autosomal.Use allele in a sentence. From German Allelshortened from Allelomorphfrom English allelomorph. Sentences Sentence examples. By continuing, you agree to our Terms of Use and Privacy Policy. Please set a username for yourself. People will see it as Author Name with your public flash cards.

The definition of alleles are pairs or series of genes on a chromosome that determine the hereditary characteristics. YourDictionary definition and usage example. Link to this page. MLA Style "Allele. In YourDictionary. All rights reserved. Also called allelomorph. Any of the possible forms in which a gene for a specific trait can occur. In almost all animal cells, two alleles for each gene are inherited, one from each parent.

Paired alleles one on each of two paired chromosomes that are the same are called homozygousand those that are different are called heterozygous. In heterozygous pairings, one allele is usually dominant, and the other recessive. Complex traits such as height and longevity are usually caused by the interactions of numerous pairs of alleles, while simple traits such as eye color may be caused by just one pair.

Noun plural alleles genetics One of a number of alternative forms of the same gene occupying a given position on a chromosome. Related terms allelomorph biallelic diallelic monoallelic multiple allelism nonallelic. English Wiktionary. Any of the alternative forms of a gene or other homologous DNA sequence. Home Dictionary Definitions allele. Sentence Examples. Related Examples of Homozygous. Examples of Incomplete Dominance. Also Mentioned In. Join YourDictionary today.The sequence of nucleotides on a DNA molecule that constitutes the form of a gene at a specific spot or a chromosome.

There can be several variations of this sequence, and each of these is called an allele. In the case of the gene for eye color, for example, one allele codes for blue eyes, whereas the other may code for brown eyes. An everyday activity is one you do every day.

Thanks, English. Practice using "everyday," one word, and "every day," two words, in this fun quiz with … everyday example sentences! Words nearby allele allegraallegrettoallegriallegroallegro, l'alleleallelic geneallelomorphallelopathyallelotaxisalleluia.

Derived forms of allele allelicadjective allelismnoun. One member of a pair or series of genes that occupies a specific position on a specific chromosome. Published by Houghton Mifflin Company. Any of the possible forms in which a gene for a specific trait can occur. In almost all animal cells, two alleles for each gene are inherited, one from each parent.

Paired alleles one on each of two paired chromosomes that are the same are called homozygousand those that are different are called heterozygous. In heterozygous pairings, one allele is usually dominant, and the other recessive. Complex traits such as height and longevity are usually caused by the interactions of numerous pairs of alleles, while simple traits such as eye color may be caused by just one pair.

All rights reserved.Allelealso called allelomorphany one of two or more genes that may occur alternatively at a given site locus on a chromosome. Alleles may occur in pairs, or there may be multiple alleles affecting the expression phenotype of a particular trait.

The combination of alleles that an organism carries constitutes its genotype. A dominant allele will override the traits of a recessive allele in a heterozygous pairing.

Allele Definition: Lesson for Kids

In some traits, however, alleles may be codominant —i. Persons with neither are type O. Most traits are determined by more than two alleles.

allele definition simple

Multiple forms of the allele may exist, though only two will attach to the designated gene site during meiosis. Also, some traits are controlled by two or more gene sites. Both possibilities multiply the number of alleles involved. All genetic traits are the result of the interactions of alleles.

allele definition simple

Mutationcrossing over, and environmental conditions selectively change the frequency of phenotypes and thus their alleles within a population. For example, alleles that are carried by individuals with high fitness meaning they successfully reproduce and pass their genes to their offspring have a higher likelihood of persisting in a population than alleles carried by less-fit individuals, which are gradually lost from the population over time. Article Media. Info Print Cite.

Submit Feedback. Thank you for your feedback. Allele biology. See Article History. Learn More in these related Britannica articles:. The MN gene pool of a particular population is specified by giving the frequencies of the alleles M and N. Thus, in the United States the M allele occurs in people of European descent with a frequency of 0.

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If alternative alleles alternative DNA sequences have identical fitness—if they are identically able to perform their function—changes in allelic frequency from generation to generation will occur only by genetic drift. Rates of allelic substitution will be stochastically constant—that is, they will occur with a constant probability for…. For example, in the case of the first gene, in the ancestral population all alleles are Aand in the evolved population all are a. For a to replace…. History at your fingertips.

Sign up here to see what happened On This Dayevery day in your inbox! Email address. By signing up, you agree to our Privacy Notice. Be on the lookout for your Britannica newsletter to get trusted stories delivered right to your inbox. More About.An allele is an alternative form of a gene one member of a pair that is located at a specific position on a specific chromosome. These DNA codings determine distinct traits that can be passed on from parents to offspring through sexual reproduction.

The process by which alleles are transmitted was discovered by scientist and abbot Gregor Mendel — and formulated in what is known as Mendel's law of segregation. Diploid organisms typically have two alleles for a trait. When allele pairs are the same, they are homozygous. When the alleles of a pair are heterozygousthe phenotype of one trait may be dominant and the other recessive. The dominant allele is expressed and the recessive allele is masked. In heterozygous relationships where neither allele is dominant but both are completely expressed, the alleles are considered to be co-dominant.

Co-dominance is exemplified in AB blood type inheritance. When one allele is not completely dominant over the other, the alleles are said to express incomplete dominance. Incomplete dominance is exhibited in pink flower color inheritance from red and white tulips. While most genes exist in two allele forms, some have multiple alleles for a trait. A common example of this in humans is ABO blood type. Human blood type is determined by the presence or absence of certain identifiers, called antigens, on the surface of red blood cells.

Individuals with blood type A have A antigens on blood cell surfaces, those with type B have B antigens, and those with type O have no antigens.

How Do Alleles Determine Traits in Genetics?

These multiple alleles are passed from parent to offspring such that one allele is inherited from each parent. The O blood type is homozygous recessive containing two I O alleles. Polygenic traits are traits that are determined by more than one gene.

This type of inheritance pattern involves many possible phenotypes that are determined by interactions among several alleles. Hair color, skin color, eye color, height, and weight are all examples of polygenic traits.

The genes contributing to these types of traits have equal influence and the alleles for these genes are found on different chromosomes. A number of different genotypes arise from polygenic traits consisting of various combinations of dominant and recessive alleles.

Individuals inheriting only dominant alleles will have an extreme expression of the dominant phenotype; individuals inheriting no dominant alleles will have an extreme expression of the recessive phenotype; individuals inheriting different combinations of dominant and recessive alleles will exhibit varying degrees of the intermediate phenotype.

Share Flipboard Email. Regina Bailey. Biology Expert. Regina Bailey is a board-certified registered nurse, science writer and educator. Updated August 21, Don't Look Like Your Sibs?Log in or sign up to add this lesson to a Custom Course. Log in or Sign up. Clasp your hands together, and look to see which thumb is on top. Then, see if you can roll your tongue. Lastly, look in the mirror and smile. Do you have dimples?

Hand clasping, tongue rolling and dimples or lack thereof are a few of the many traits, or inherited characteristics, that make you unique. This lesson explores traits and explains how it is that you became the person you are. Traits are determined by geneswhich are chemical instructions inherited from your parents that influence what you look like. Half of your genes came from your mom, and the other half came from your dad, giving your body a full set of instructions to build you.

Alleles are variations of a gene that can result in different traits in living things. Every trait that you have came from the genes you inherited from your parents. You are actually made of trillions of cells, which all compressed together to build you. When you were first made, you started out as a single cell that was formed by combining half of your dad's genetic material with half of your mom's genetic material. Therefore, you had two copies, or in other words two alleles, for each gene.

That left you with two sets of instructions for each gene. If you had two identical alleles for a gene, these instructions were identical, and that trait appeared. For example, if you inherited two alleles for a gigantic big toe, you'd likely have to wear big shoes your whole life because you'd have the instructions from birth for a huge toe.

If you were given two identical alleles for an average size toe, you would have an average size toe. Many genes have different alleles, which means that sometimes, the instructions are conflicting, and your body must decide which instructions it should follow.

If one allele in a pair always makes a trait appear, that allele is said to be dominant. For examples, a fruit fly can inherit an allele for eyes which is dominant or an allele that will make it eyeless. The fly will have eyes if it receives two of the dominant alleles or if it receives just one. To not develop eyes, the fruit fly would have to inherit two of the eyeless alleles.

Alleles and Genes

In other words, the allele with the dominant instructions is followed when there are conflicting instructions. Well, most of the time, the dominant allele wins out. Sometimes, a trait appears that is a blend of both instructions. For example, in flowers, a red allele and a white allele might show up as a pink flower. And other times, both instructions are followed. An example is blood type. If you have an A allele and a B allele, you'll have AB blood type.

The way you look is determined by chemical instructions called genes. Genes are inherited from your parents, and variations of genes are called alleles. If you inherit alleles with conflicting instructions, the dominant allele will typically determine the trait.

To unlock this lesson you must be a Study. Create your account.Definition noun, plural: alleles genetics One member of a pair or any of the series of gene s occupying a specific spot on a chromosome called locus that controls the same trait Supplement Alleles are the pairs of gene s occupying a specific spot on a chromosome. That spot is called locus. For example, a pair of alleles controlling the same traiti.

In human s, simple trait s such as eye color may be caused by the interaction of only one pair of alleles. But for complex trait s, such as heightthey are usually caused by the interaction s of series of alleles. Some alleles are dominant over other alleles, as in the case of heterozygous pairings where paired alleles are different, in contrast to homozygous pairings where alleles are the same.

In the above example, since the alleles code for different eye colors they are heterozygous. This tutorial describes the independent assortment of chromosomes and crossing over as important events in meiosis. Read this tutorial to know more details in each of these meiotic events and how they promote genetic diversity in sexually-reproducing organisms Read More.

Darwin's Finches are an example of natural selection in action. They are an excellent example of the way species' gene pools have adapted in order for long term survival via their offspring.

See this tutorial for more elaborate info on natural selection as exemplified by Darwin's finches Genes are expressed through the process of protein synthesis. This elaborate tutorial provides an in-depth review of the different steps of the biological production of protein starting from the gene up to the process of secretion.

Also included are topics on DNA replication during interphase of the cell cycle, DNA mutation and repair mechanisms, gene pool, modification, and diseases According to Charles Darwin's theory of natural selection, preferable genes are favored by nature in the gene pool, and over time, these preferable characteristics become more exclusive in the gene pool. This tutorial rounds up all the factors that can alter the makeup of a gene pool One of Mendel's law of inheritance is the "law of dominance".

There are certain cases though that this pattern is not observed, such as in the case of incomplete dominance and codominance. Read this tutorial to know more about Mendelian and non-Mendelian form of inheritance This means that for every chromosome in the body, there is another one to match it. However, there are organisms that have more than two sets of chromosomes.

allele definition simple


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