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What is the difference between dominant and recessive alleles?

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Quick Answer

Dominant alleles are always expressed in the organism, while recessive traits tend to be expressed only when the dominant allele is not present. The relationship between dominant and recessive genes is described by the Law of Segregation. As related by About.com, Gregor Mendel observed nine different traits among his pea plants and found that certain traits, such as pod color, bred true only when two recessive alleles were present.

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What is the difference between dominant and recessive alleles?
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Full Answer

Sexually reproducing organisms carry two copies of each gene in their DNA. When these two copies are the same, or "homozygous," their effect is to produce whatever trait the genes are identified with. When different versions of the gene are paired, however, what usually happens is that one gene is expressed at the expense of the other. The expressed trait is then described as dominant.

By carefully isolating nine separate traits in his pea plants, Mendel was able to show that each trait--such as plant height and pod color--bred true in self-fertilized plants. When the plants were cross-fertilized, however, their traits did not blend; tall and short plants didn't produce medium-height plants, for example. Instead, according to Genome.gov, three out of four offspring were tall. In this case, tall was a dominant allele.

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    What is an intermediate phenotype?

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    What is an allele?

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    An allele is an alternative form of a gene that is located at a specific position on a specific chromosome. Mendel's law of segregation formulates the process by which an allele is transmitted.

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    How many alleles are there for blood type?

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    What is a heterozygous genotype?

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    According to Kansas State University, heterozygous genotypes are those that feature non-identical alleles for a given pair of genes. The term is most often used to describe an organism that has one copy of a recessive gene and one copy of a dominant gene. Because recessive traits are only expressed in an organism’s phenotype if they occur in pairs, such organisms appear normal, even though they possess the recessive gene.

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