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Autosomal dominant A 50/50 chance of inheritance. Sickle-cell disease is inherited in the autosomal recessive pattern. When both parents have sickle-cell trait (carrier), a child has a 25% chance of sickle-cell disease (red icon), 25% do not carry any sickle-cell alleles (blue icon), and 50% have the heterozygous (carrier) condition. [1]
Sex-influenced or sex-conditioned traits are phenotypes affected by whether they appear in a male or female body. [6] Even in a homozygous dominant or recessive female the condition may not be expressed fully. Example: baldness in humans.
A popular example showing this pattern of inheritance is that of the descendants of Queen Victoria and the blood disease hemophilia. [3] The last pattern seen is that X-linked recessive traits tend to skip generations, meaning that an affected grandfather will not have an affected son, but could have an affected grandson through his daughter. [4]
Mendelian traits behave according to the model of monogenic or simple gene inheritance in which one gene corresponds to one trait. Discrete traits (as opposed to continuously varying traits such as height) with simple Mendelian inheritance patterns are relatively rare in nature, and many of the clearest examples in humans cause disorders.
Autosomal recessive inheritance, a 25% chance. Autosomal recessive traits is one pattern of inheritance for a trait, disease, or disorder to be passed on through families. For a recessive trait or disease to be displayed two copies of the trait or disorder needs to be presented. The trait or gene will be located on a non-sex chromosome.
In a dominant-recessive inheritance, an average of 25% are homozygous with the dominant trait, 50% are heterozygous showing the dominant trait in the phenotype (genetic carriers), 25% are homozygous with the recessive trait and therefore express the recessive trait in the phenotype. The genotypic ratio is 1: 2 : 1, and the phenotypic ratio is 3: 1.
Individuals can develop a recessive trait in the phenotype dependent on their sex—for example, colour blindness and haemophilia (see gonosomal inheritances). [ 7 ] [ 8 ] As many of the alleles are dominant or recessive, a true understanding of the principles of Mendelian inheritance is an important requirement to also understand the more ...
An example of a pedigree for an autosomal dominant condition. Other conditions are inherited in an autosomal recessive pattern, where affected individuals do not typically have an affected parent. Since each parent must have a copy of the recessive allele in order to have an affected offspring, the parents are referred to as carriers of the ...