How to do trihybrid punnett square wwith linked genes
Genetics Linked Genes Preamble Linked genes are genes located on the same chromosomes and are inherited together. However, in the production of gametes, linked genes may be separated by crossing over during meiosis leading to some amount of independent assortment of the linked genes. For a particular species of plants, let us consider three characteristics: plant height (tall, dwarf), seed shape (round, wrinkled) and seed color (yellow, green). In this species of plant, the genes for plant height and seed shape are located on the same chromosome while the gene for seed color is on another chromosome. Plant height is controlled by two alleles with tall (T) being completely dominant to dwarf (t). A second pair of alleles control seed shape with round (R) being completely dominant to wrinkled (r). A third pair of alleles control seed color with yellow (Y) being completely dominant to green (y). If true-breeding plants that are tall and producing round, yellow seeds are crossed with true-breeding dwarf plants producing wrinkled, green seeds, the F1 progeny will be all tall plants producing round, yellow seeds. If this F1 progeny is allowed to self-fertilize, the expected genotypic and phenotypic ratios in the resulting F2 generation will be different from those expected in a normal trihybrid cross in accordance with the laws of segregation and independent assortment of the different alleles. Exercise: Suppose that an experiment is carried out where true-breeding plants (of the particular species mentioned above) that are tall and producing round, yellow seeds are crossed with true-breeding dwarf plants producing wrinkled, green seed and the F1 progeny is then allowed to self-fertilize to produce an F2 generation. With the aid of a Punnett Square, determine the expected genotypic and phenotypic ratios in the F2 generation (assume no separation of linked genes by crossing over).