A Drosophila experiment examining potential genetic linkage of X-linked genes studies a recessive eye mutant (echinus), a recessive wing-vein mutation (crossveinless), and a recessive bristle mutation (scute). The wild-type phenotypes are dominant. Trihybrid wild-type females (all have the same genotype) are crossed to hemizygous males displaying the three recessive phenotypes. Among the 20,765 progeny produced from these crosses are the phenotypes and numbers listed in the table. Any phenotype not given is wild type.Phenotype Number1. Echinus 85762. Scute 9773. Crossveinless 7164. Echinus, scute 6815. Scute, crossveinless 88086. Scute, crossveinless, echinus 47. Echinus, crossveinless 10028. Wild type 120,765Compare the recombination frequencies and speculate about the source of any apparent discrepancies in the recombination data.

Three dominant traits of corn seedlings, tunicate seed (T-), glossy appearance (G-), and liguled stem (L-), are studied along with their recessive counterparts, nontunicate (tt), nonglossy (gg), and liguleless (ll). A trihybrid plant with the three dominant traits is crossed to a nontunicate, nonglossy, liguleless plant. Kernels on ears of progeny plants are scored for the traits, with the following results:

Phenotype                                     Number
Tunicate, glossy, liguled                   102
Tunicate, glossy, liguleless               106
Tunicate, nonglossy, liguled               18
Tunicate, nonglossy, liguleless           20
Nontunicate, glossy, liguled                22
Nontunicate, glossy, liguleless            23
Nontunicate, nonglossy, liguled           99
Nontunicate, nonglossy, liguleless     110
                                                           500

Is there evidence of genetic linkage among any of these gene pairs? If so, identify the evidence.

T. H. Morgan's data on eye color and wing form, shown in Figures 5.3 and 5.5, reveal genetic linkage between the two genes. Test this genetic linkage data with chi-square analysis, and show that the results are significantly different from the expectation under the assumption of independent assortment.

The accompanying pedigree below shows a family in which an autosomal recessive disorder is present. Family members I-2 and II-2 are affected by the disorder and have the genotype dd. A pregnancy involving II-4 has just undergone genetic testing for a VNTR that is linked to the disease gene. The VNTR has a recombination frequency of r = 20 with the disease gene. The VNTR has two alleles, V₁ and V₂. The gel electrophoresis patterns for each family member are shown, including the VNTR genotype for II-4. Based on the information given, answer the following questions about the family.

What is the chance II-4 has the disease?

The accompanying pedigree below shows a family in which an autosomal recessive disorder is present. Family members I-2 and II-2 are affected by the disorder and have the genotype dd. A pregnancy involving II-4 has just undergone genetic testing for a VNTR that is linked to the disease gene. The VNTR has a recombination frequency of r = 20 with the disease gene. The VNTR has two alleles, V₁ and V₂. The gel electrophoresis patterns for each family member are shown, including the VNTR genotype for II-4. Based on the information given, answer the following questions about the family.

What are the syntenic disease gene and VNTR alleles in I-1 and I-2?