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Autosomal dominant and autosomal recessive inheritance, the two most common Mendelian inheritance patterns. An autosome is any chromosome other than a sex chromosome.. In genetics, dominance is the phenomenon of one variant of a gene on a chromosome masking or overriding the effect of a different variant of the same gene on the other copy of the chromosome.
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.
Fur color in domestic cats: the gene that causes orange pigment is on the X chromosome; thus a Calico or tortoiseshell cat, with both black (or gray) and orange pigment, is nearly always female. The first sex-linked gene ever discovered was the "lacticolor" X-linked recessive gene in the moth Abraxas grossulariata by Leonard Doncaster. [4]
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.
This is often through some sort of masking effect of one gene on the other. [22] For example, the "A" gene codes for hair color, a dominant "A" allele codes for brown hair, and a recessive "a" allele codes for blonde hair, but a separate "B" gene controls hair growth, and a recessive "b" allele causes baldness.
Recessive genetic disorders include albinism, cystic fibrosis, galactosemia, phenylketonuria (PKU), and Tay–Sachs disease. Other disorders are also due to recessive alleles, but because the gene locus is located on the X chromosome, so that males have only one copy (that is, they are hemizygous ), they are more frequent in males than in females.
An individual that is homozygous-recessive for a particular trait carries two copies of the allele that codes for the recessive trait. This allele, often called the "recessive allele", is usually represented by the lowercase form of the letter used for the corresponding dominant trait (such as, with reference to the example above, "p" for the ...
An example pedigree chart of an autosomal dominant disorder An example pedigree chart of an autosomal recessive disorder An example pedigree chart of a sex-linked disorder (The gene is on the X chromosome.) The description of a mode of biological inheritance consists of three main categories: 1. Number of involved loci