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Punnett square
The Punnett square is a diagram that is used to predict an outcome of a particular cross or breeding experiment. It is named after Reginald C. Punnett, who devised the approach. The diagram is used by biologists to determine the probability of an offspring having a particular genotype. The Punnett square is a tabular summary of possible combinations of maternal alleles with paternal alleles. 〔(Introducing Punnett Squares )〕 These tables can be used to examine the genotypic outcome probabilities of the offspring of a single trait (allele), or when crossing multiple traits from the parents. The Punnett Square is a visual representation of Mendelian inheritance. It is important to understand the terms "heterozygous", "homozygous", "double heterozygote" (or homozygote), "dominant allele" and "recessive allele" when using the Punnet square method. For multiple traits, using the "forked-line method" is typically much easier than the Punnett square. Phenotypes may be assessed using a Punnet square, but the phenotype that may appear from a given genotype can be influenced by many other factors.
==Monohybrid cross==
(詳細はIn this example, both parents have the genotype ''Bb''. For the example of eye color we stated above, this would mean they both have brown eyes. They can produce gametes that contain either the ''B'' or the ''b'' allele. (It is conventional in genetics to use capital letters to indicate dominant alleles and lower-case letters to indicate recessive alleles.) The probability of an individual offspring's having the genotype ''BB'' is 25%, ''Bb'' is 50%, and ''bb'' is 25%. The ratio of the phenotypes is 3:1, typical for a monohybrid cross. When assessing phenotype from this, "3" of the offspring will exhibit the "Brown" eyes and only one offspring will exhibit the "green" eyes. (3 are "B_" and 1 is "bb")
''(M = Maternal, P = Paternal)''
The way in which the ''B'' and ''b'' alleles interact with each other to affect the appearance of the offspring depends on how the gene products (proteins) interact (see Mendelian inheritance). This can be things like lethal effects and epistasis (where one allele masks another, regardless of dominant or recessive status).
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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