If AAbb ,aaBB , AaBb produces same phenotype then what type of inheritance is it
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Answer:
In his dihybrid crosses with pea plants, Gregor Mendel simultaneously examined two different genes that controlled two different traits. For instance, in one series of experiments, Mendel began by crossing a plant that was homozygous for both round seed shape and yellow seed color (RRYY) with another plant that was homozygous for both wrinkled seed shape and green seed color (rryy). Then, when Mendel crossed two of the F1 progeny plants with each other (RrYy × RrYy), he obtained an F2 generation with a phenotypic ratio of 9:3:3:1, as summarized in Table 1.
In this dihybrid cross, each gene locus had an independent effect on a single phenotype. Thus, the R and r alleles affected only the shape of the seed and had no influence on seed color, while the Y and y alleles affected only seed color and had no influence on seed shape. In this case, there were two separate genes that coded for two separate characteristics.
But what happens when two different loci affect the same characteristic? For instance, what if both of the loci in Mendel's experiment affected seed color? When two genes are involved in the outcome of one characteristic, a dihybrid cross involving these genes can produce a phenotypic ratio very different from 9:3:3:1. Under these circumstances, there are more than two gene products affecting the same phenotype, and these products may have complex hierarchical relationships. Any time two different genes contribute to a single phenotype and their effects are not merely additive, those genes are said to be epistatic.
Although some researchers have attempted to categorize all digenic (two-gene) epistatic interactions with specific names, those classification schemes are seldom used today. One reason that they have fallen out of favor is that terms such as "dominant" and "recessive" are best used to describe the effects of alleles of single genes. Furthermore, epitasis is not restricted to the interactions of only two genes. Rather, epistasis occurs in all of the following scenarios:
Whenever two or more loci interact to create new phenotypes
Whenever an allele at one locus masks the effects of alleles at one or more other loci
Whenever an allele at one locus modifies the effects of alleles at one or more other loci
Epistasis is an interaction at the phenotypic level of organization. The genes that are involved in a specific epistatic interaction may still show independent assortment at the genotypic level. In such cases, however, the phenotypic ratios may appear to deviate from those expected with independent assortment.
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