Exception of law of dominance:

  • Incomplete dominance: In incomplete dominance when a red snapdragon flowered plant is crossed with a white flowered plant an intermediate phenotype appears in the F1 hybrid instead of a parental phenotype.
  • Codominance: Unlike dominance in codominance when a A (I^AI^A) blood group individual mates with B (I^BI^B) blood group individual the offsprings have blood group AB (I^AI^B) instead of A or B.
  • epistasis: Allelic effect at a given locus depend on the variants at other loci
  • environment dependence and specific case of frequency dependence:The concept of dominance can be used for any quantitative trait. Typically, when the quantitative trait of interest is fitness, then the trait often depend on the environment. A typical and interesting case is when the fitness depends on the frequency of alleles in the population. Depending of the frequency of the allele at a given locus, the relationship might be a relationship of dominance, additivity or dominance for the other allele.

Exception of law of segregation:

  • Nondysjunction: During meiosis homologous chromosomes/sister chromatids and hence genes may move to a common gamete violating law of segregation.
  • Meiotic drive: Meiotic drive is a type of intragenomic conflict, whereby one or more loci within a genome will affect a manipulation of the meiotic process in such a way as to favor the transmission of one or more alleles over another, regardless of its phenotypic expression. More simply, meiotic drive is when one copy of a gene is passed on to offspring more than the expected 50% of the time

Exception of law of independent assortment:

  • Linkage: When genes are present on the same chromosome they tend to remain together and enter into the same gamete. This is the reason behind deviation of dihybrid test cross ratio from 1:1:1:1 and occurrence of parental combination in high frequencies.
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