The gene controlling the Xg blood group alleles (Xg⁺ and Xg⁻) and the gene controlling a newly described form of inherited recessive muscle weakness called episodic muscle weakness (EMWX) (Ryan et al., 1999) are closely linked on the X chromosome in humans at position Xp22.3 (the tip of the short arm). A male with EMWX who is Xg⁻ marries a woman who is Xg⁺ and they have eight daughters and one son, all of whom are normal for muscle function, the male being Xg⁺ and all the daughters being heterozygous at both the EMWX and Xg loci. Following is a table that lists three of the daughters with the phenotypes of their husbands and children.For each of the offspring, indicate whether or not a crossover was required to produce the phenotypes that are given.

In experiments published in 1918 that sought to verify and expand the genetic linkage and recombination theory proposed by Morgan, Thomas Bregger studied potential genetic linkage in corn (Zea mays) for genes controlling kernel color (colored is dominant to colorless) and starch content (starchy is dominant to waxy). Bregger performed two crosses. In Cross 1, pure-breeding colored, starchy-kernel plants (C1 Wx/C1 Wx) were crossed to plants pure-breeding for colorless, waxy kernels (c1 wx/c1 wx). The F₁ of this cross were test-crossed to colorless, waxy plants. The test-cross progeny were as follows:

Phenotype                            Number
Colored, waxy                         310
Colored, starchy                      858
Colorless, waxy                       781
Colorless, starchy                    311
                                               2260

In Cross 2, plants pure-breeding for colored, waxy kernels (C1 wx/C1 wx) and colorless, starchy kernels (c1 Wx/c1 Wx) were mated, and their F₁ were test-crossed to colorless, waxy plants. The test-cross progeny were as follows:

Phenotype                           Number
Colored, waxy                        340
Colored, starchy                     115
Colorless, waxy                        92
Colorless, starchy                   298
                                               845

Merge the two sets of progeny data and determine the combined recombination frequency.

In experiments published in 1918 that sought to verify and expand the genetic linkage and recombination theory proposed by Morgan, Thomas Bregger studied potential genetic linkage in corn (Zea mays) for genes controlling kernel color (colored is dominant to colorless) and starch content (starchy is dominant to waxy). Bregger performed two crosses. In Cross 1, pure-breeding colored, starchy-kernel plants (C1 Wx/C1 Wx) were crossed to plants pure-breeding for colorless, waxy kernels (c1 wx/c1 wx). The F₁ of this cross were test-crossed to colorless, waxy plants. The test-cross progeny were as follows:

Phenotype                            Number
Colored, waxy                         310
Colored, starchy                      858
Colorless, waxy                       781
Colorless, starchy                    311
                                               2260

In Cross 2, plants pure-breeding for colored, waxy kernels (C1 wx/C1 wx) and colorless, starchy kernels (c1 Wx/c1 Wx) were mated, and their F₁ were test-crossed to colorless, waxy plants. The test-cross progeny were as follows:

Phenotype                           Number
Colored, waxy                        340
Colored, starchy                     115
Colorless, waxy                        92
Colorless, starchy                   298
                                               845

Taken together, are the results of these two experiments compatible with the hypothesis of genetic linkage? Explain why or why not.

In experiments published in 1918 that sought to verify and expand the genetic linkage and recombination theory proposed by Morgan, Thomas Bregger studied potential genetic linkage in corn (Zea mays) for genes controlling kernel color (colored is dominant to colorless) and starch content (starchy is dominant to waxy). Bregger performed two crosses. In Cross 1, pure-breeding colored, starchy-kernel plants (C1 Wx/C1 Wx) were crossed to plants pure-breeding for colorless, waxy kernels (c1 wx/c1 wx). The F₁ of this cross were test-crossed to colorless, waxy plants. The test-cross progeny were as follows:

Phenotype                            Number
Colored, waxy                         310
Colored, starchy                      858
Colorless, waxy                       781
Colorless, starchy                    311
                                               2260

In Cross 2, plants pure-breeding for colored, waxy kernels (C1 wx/C1 wx) and colorless, starchy kernels (c1 Wx/c1 Wx) were mated, and their F₁ were test-crossed to colorless, waxy plants. The test-cross progeny were as follows:

Phenotype                           Number
Colored, waxy                        340
Colored, starchy                     115
Colorless, waxy                        92
Colorless, starchy                   298
                                               845

Calculate the recombination frequency for each of the progeny groups.

In experiments published in 1918 that sought to verify and expand the genetic linkage and recombination theory proposed by Morgan, Thomas Bregger studied potential genetic linkage in corn (Zea mays) for genes controlling kernel color (colored is dominant to colorless) and starch content (starchy is dominant to waxy). Bregger performed two crosses. In Cross 1, pure-breeding colored, starchy-kernel plants (C1 Wx/C1 Wx) were crossed to plants pure-breeding for colorless, waxy kernels (c1 wx/c1 wx). The F₁ of this cross were test-crossed to colorless, waxy plants. The test-cross progeny were as follows:

Phenotype                            Number
Colored, waxy                         310
Colored, starchy                      858
Colorless, waxy                       781
Colorless, starchy                    311
                                               2260

In Cross 2, plants pure-breeding for colored, waxy kernels (C1 wx/C1 wx) and colorless, starchy kernels (c1 Wx/c1 Wx) were mated, and their F₁ were test-crossed to colorless, waxy plants. The test-cross progeny were as follows:

Phenotype                           Number
Colored, waxy                        340
Colored, starchy                     115
Colorless, waxy                        92
Colorless, starchy                   298
                                               845

For each set of test-cross progeny, determine whether genetic linkage or independent assortment is more strongly supported by the data. Explain the rationale for your answer.

Divide a clean sheet of paper into four quadrants and draw one pair of homologous chromosomes in each quadrant. Draw the chromosomes with two sister chromatids each. The four sets of homologous pairs are identical. Label one chromosome of each pair with alleles A₁ and A₂  and the other member of each pair with the alleles A₁ and A₂. You are to illustrate a single crossover between the homologs in each quadrant and list the parental and recombinant chromosomes, but you are to illustrate four different ways the crossover can occur by involving different chromatids in each illustration.

Which of the following gametes can be formed from the genotype AaBb if AB and ab are linked?

An experiment that was performed found the recombination frequency between two genes was 12.5%. What is the distance (in mapping units) between two genes?

Which of the following terms describes two copies of the same chromosome?