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Heterozygous genotypes are represented by an uppercase letter (representing the dominant/wild-type allele) and a lowercase letter (representing the recessive/mutant allele), as in "Rr" or "Ss". Alternatively, a heterozygote for gene "R" is assumed to be "Rr". The uppercase letter is usually written first. [citation needed]
For example, using 'A' as the representative character for each allele, a homozygous dominant pair's genotype would be depicted as 'AA', while homozygous recessive is shown as 'aa'. Heterozygosity, with hetero associated with different , can only be 'Aa' (the capital letter is always presented first by convention).
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.
An uppercase letter is typically used to represent the dominant allele, and a lowercase letter is used to represent the recessive allele. The possible genotypes of the offspring can then be determined by combining the parent genotypes. [10] In the example on the right, both parents are heterozygous, with a genotype of Bb.
Under the law of dominance in genetics, an individual expressing a dominant phenotype could contain either two copies of the dominant allele (homozygous dominant) or one copy of each dominant and recessive allele (heterozygous dominant). [1] By performing a test cross, one can determine whether the individual is heterozygous or homozygous ...
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.
Figure 1: Inheritance pattern of dominant (red) and recessive (white) phenotypes when each parent (1) is homozygous for either the dominant or recessive trait. All members of the F 1 generation are heterozygous and share the same dominant phenotype (2), while the F 2 generation exhibits a 6:2 ratio of dominant to recessive phenotypes (3).
In an individual which is heterozygous regarding a certain allele, it is not externally recognisable that it also has the recessive allele. But if the carrier has a child, the recessive trait appears in the phenotype, in case the descendant receives the recessive allele from both parents and therefore does not possess the dominant allele that ...