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• Non-Mendelian genetics are any inheritance patterns that don't follow one or more laws of Mendelian genetics.
• The pattern of inheritance described by Mendel in his experiments all show complete dominance.
• The Himalayan c h allele is completely dominant to the albino c allele.
• The black C allele is completely dominant to all the others.
• Biologists, after Mendel, have discovered other models of inheritance and expression.
• The chinchilla c ch allele is incompletely dominant to the Himalayan c h and albino c alleles.
• Incomplete dominance is a non-Mendelian pattern of inheritance where the phenotype of a heterozygous organism can be a blend between the phenotypes of its homozygous parents.
• For example, in the snapdragon, Antirrhinum majus, a cross between a homozygous white-flowered plant (CWCW) and a homozygous red-flowered plant (CRCR) will produce offspring with pink flowers (CRCW).
• This type of relationship between alleles, with a heterozygote phenotype intermediate between the two homozygote phenotypes, is called incomplete dominance.
• We can still use Mendel's model to predict the results of crosses for alleles that show incomplete dominance.
• For example, self-fertilization of a pink plant would produce a genotype ratio of 1 CRCR: 2 CRCW: 1 CWCW and a phenotype ratio of 1:2:1 – red: pink: white.
• Alleles are still inherited according to Mendel's basic rules, even when they show incomplete dominance.
• In incomplete dominance, the heterozygous plant was actually blending the "dominant" and "recessive" alleles instead of the dominant trait completely masking the recessive trait in the phenotype of the plant.
• If red and white are blended, the color pink results, just as it does in the snapdragon flower color.
• This condition gives the cattle a reddish color and is referred to as Roan (BW).
• Alleles are approximately equal effect in individuals; alleles are equally detectable in individuals.
• The codominance is written as C B C B x C O C O = 100% C B C O.
• The hybrid shows neither of the parents’ trait, instead, a third, different phenotype.
• Co- means together codominant means equal in dominance.
• An example of multiple alleles of a gene is the C series in rabbits.
• A gene can have more than two allelic forms segregating within a population.
• In Mendel's studies, he proposed that there are two alleles for every gene, the dominant of the two having its phenotype expressed in a heterozygote.
• An c ch c ch rabbit has chinchilla coloration, with grayish fur.
• The genotype for fur can be represented as CB or CO.
• A CC rabbit has black or brown fur.
• An cc rabbit is albino, with a pure white coat.
• Multiple alleles make for many possible dominance relationships.
• An individual can only have a maximum of two of the alleles, one maternal and one paternal, no matter how many alleles exist in the population.
• Crossing two wavy haired individuals results in a phenotype that is a combination of both parents' traits.
• Cattle can either be all red RR; all white WW or Roan RWN.
• Common phenotype used is roan fur in cattle.
• C B is for black color and C O denotes orange color.
• In some cattle the genes for brown hair (B) and for white hair (W) are co-dominant.
• Phenotypes for both alleles are exhibited in the heterozygote.
• These genes are referred to as having multiple alleles.
• More than three alleles are referred to as having multiple alleles.
• Cattle with alleles for both brown and white hair, have both brown and white hairs.
• An c h c h rabbit has Himalayan (color-point) patterning, with a white body and dark ears, face, feet, and tail.
• In Codominance, both alleles in the heterozygotes express themselves fully.