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Example of a pedigree chart using Ahnentafel numbering. A pedigree chart is a diagram that shows the occurrence and appearance of phenotypes [jargon] of a particular gene or organism and its ancestors from one generation to the next, [1] [2] [3] [unreliable source?] most commonly humans, show dogs, and race horses.
An example of a family pedigree displaying an autosomal recessive trait. A pedigree is a diagram showing the ancestral relationships and transmission of genetic traits over several generations in a family. Square symbols are almost always used to represent males, whilst circles are used for females.
Mendelian traits in humans. 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]
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.
In humans, inheritance of X-linked recessive traits follows a unique pattern made up of three points. The first is that affected fathers cannot pass X-linked recessive traits to their sons because fathers give Y chromosomes to their sons. This means that males affected by an X-linked recessive disorder inherited the responsible X chromosome ...
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 ...
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 genetic disorders which exhibit Mendelian inheritance can be inherited either in an autosomal dominant or recessive fashion. [7] These disorders manifest in and are passed on by either sex with equal frequency. [7] [8] Autosomal dominant disorders are often present in both parent and child, as the child needs to inherit only one copy ...