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An allele [1], or allelomorph, is a variant of the sequence of nucleotides at a particular location, ... [10] and the other allele is said to be "recessive". The ...
Thus, allele R is dominant over allele r, and allele r is recessive to allele R. [4] Dominance is not inherent to an allele or its traits . It is a strictly relative effect between two alleles of a given gene of any function; one allele can be dominant over a second allele of the same gene, recessive to a third, and co-dominant with a fourth.
Illustration of some X-linked heredity outcomes (A) the affected father has one X-linked dominant allele, the mother is homozygous for the recessive allele: only daughters (all) will be affected. (B) the affected mother is heterozygous with one copy of the X-linked dominant allele: both daughters and sons will have 50% probability to be ...
According to the model of Mendelian inheritance, alleles may be dominant or recessive, one allele is inherited from each parent, and only those who inherit a recessive allele from each parent exhibit the recessive phenotype. Offspring with either one or two copies of the dominant allele will display the dominant phenotype.
Since the homozygous recessive individual can only pass on recessive alleles, the allele the individual in question passes on determines the phenotype of the offspring. [3] Thus, this test yields 2 possible situations: If any of the offspring produced express the recessive trait, the individual in question is heterozygous for the dominant ...
In the example on the right, both parents are heterozygous, with a genotype of Bb. The offspring can inherit a dominant allele from each parent, making them homozygous with a genotype of BB. The offspring can inherit a dominant allele from one parent and a recessive allele from the other parent, making them heterozygous with a genotype of Bb.
Normally, two recessive alleles need to be inherited (one from each parent) for the recessive trait to be expressed but recessive merely means that the trait is only expressed in the absence of the dominant alleles. The pattern of inheritance in which a single recessive allele is inherited but is still expressed is known as pseudodominance.
Achondroplasia is a skeletal system disorder caused by a recessive allele that can still result in a live birth in the homozygous state. [8] One mutant allele for achondroplasia can be tolerated, but having two results in death. In the case of homozygous achondroplasia, death almost invariably occurs before birth or in the perinatal period.