![]() ![]() To a lesser degree, hemizygosity and nullizygosity can also be seen in gene pairs. Heterozygous pairs always have a dominant phenotype. The phenotype of a homozygous dominant pair is 'A', or dominant, while the opposite is true for homozygous recessive. Heterozygosity, with hetero associated with different, can only be 'Aa' (the capital letter is always presented first by convention). 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'. Homozygosity, with homo relating to same while zygous pertains to a zygote, is seen when a combination of either two dominant or two recessive alleles code for the same trait. In its simplest form, a pair of alleles can be either homozygous or heterozygous. Zygosity refers to the grade of similarity between the alleles that determine one specific trait in an organism. Phenotypes may be predicted with at least better-than-chance accuracy using a Punnett square, but the phenotype that may appear in the presence of a given genotype can in some instances be influenced by many other factors, as when polygenic inheritance and/or epigenetics are at work. For multiple traits, using the "forked-line method" is typically much easier than the Punnett square. It is important to understand the terms "heterozygous", "homozygous", "double heterozygote" (or homozygote), "dominant allele" and "recessive allele" when using the Punnett square method. The Punnett square is a visual representation of Mendelian inheritance. These tables can be used to examine the genotypical outcome probabilities of the offspring of a single trait (allele), or when crossing multiple traits from the parents. ![]() The Punnett square is a tabular summary of possible combinations of maternal alleles with paternal alleles. The diagram is used by biologists to determine the probability of an offspring having a particular genotype. Punnett, who devised the approach in 1905. The Punnett square is a square diagram that is used to predict the genotypes of a particular cross or breeding experiment. ![]() Punnett squares for each combination of parents' colour vision status giving probabilities of their offsprings' status, each cell having 25% probability in theory. ![]()
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