In a diploid species of plant, the genes for plant height and fruit shape are syntenic and separated by 18 m.u. Allele D produces tall plants and is dominant to d for short plants, and allele R produces round fruit and is dominant to r for oval fruit.

Give the same information for a plant with the genotype Dr/dR.

Genes E and H are syntenic in an experimental organism with the genotype EH/eh. Assume that during each meiosis, one crossover occurs between these genes. No homologous chromosomes escape crossover, and none undergo double crossover. Are genes E and H genetically linked? Why or why not? What is the proportion of parental gametes produced by meiosis?

Genes A, B, and C are linked on a chromosome and found in the order A–B–C. Genes A and B recombine with a frequency of 8%, and genes B and C recombine at a frequency of 24%. For the cross a⁺b⁺c/abc⁺×abc/abc, predict the frequency of progeny genotypes. Assume interference is zero.

Gene G recombines with gene T at a frequency of 7%, and gene G recombines with gene R at a frequency of 4%.

Draw two possible genetic maps for these three genes, and identify the recombination frequencies predicted for each map.

Gene G recombines with gene T at a frequency of 7%, and gene G recombines with gene R at a frequency of 4%.

Assuming that organisms with any desired genotype are available, propose a genetic cross whose result could be used to determine which of the proposed genetic maps is correct.

Determine whether the statements below are true or false. If a statement is false, provide the correct information or revise the statement to make it correct.

The progeny of a trihybrid cross are expected to have one of 27 different genotypes.

Alleles A and a are on one pair of autosomes, and alleles B and b are on a separate pair of autosomes. Does crossover between one pair of homologs affect the expected proportions of gamete genotypes? Why or why not? Does crossover between both pairs of chromosomes affect the expected gamete proportions? Why or why not?

Genes A, B, C, D, and E are linked on a chromosome and occur in the order given.

Previous genetic linkage crosses have determined that recombination frequencies are 6% for genes A and B, 4% for genes B and C, 10% for genes C and D, and 11% for genes D and E. The sum of these frequencies between genes A and E is 31%. Why does the recombination distance between these genes as determined by adding the intervals between adjacent linked genes differ from the distance determined by the test cross?

Genes A, B, C, D, and E are linked on a chromosome and occur in the order given.

The test cross  indicates the genes recombine with a frequency of 28%. If 1000 progeny are produced by this test cross, determine the number of progeny in each outcome class.

Define linkage disequilibrium. What is the physical basis of linkage, and what causes linkage equilibrium? Explain how crossing over eliminates linkage disequilibrium.

Researchers cross a corn plant that is pure-breeding for the dominant traits colored aleurone (C1), full kernel (Sh), and waxy endosperm (Wx) to a pure-breeding plant with the recessive traits colorless aleurone (c1), shrunken kernel (sh), and starchy (wx). The resulting F₁ plants were crossed to pure-breeding colorless, shrunken, starchy plants. Counting the kernels from about 30 ears of corn yields the following data.

Kernel Phenotype                           Number
Colored, shrunken, starchy               116
Colored, full, waxy                             601
Colored, full, starchy                        2538
Colored, shrunken, waxy                       4
Colorless, shrunken, starchy            2708
Colorless, full, starchy                            2
Colorless, full, waxy                            113
Colorless, shrunken, waxy                  626
                                                          6708

Why are these data consistent with genetic linkage among the three genes?

You have isolated (1) a streptomycin-resistant mutant (strᴿ) of Chlamydomonas that maps to the chloroplast genome and (2) a hygromycin-resistant mutant (hygᴿ) of Chlamydomonas that maps to the mitochondrial genome. What types of progeny do you expect from the following reciprocal crosses?

mt⁺ strᴿ hygˢ× mt⁻ strˢ hygᴿ
mt⁺ strˢ hygᴿ× mt⁻ strᴿ hygSˢ

Researchers cross a corn plant that is pure-breeding for the dominant traits colored aleurone (C1), full kernel (Sh), and waxy endosperm (Wx) to a pure-breeding plant with the recessive traits colorless aleurone (c1), shrunken kernel (sh), and starchy (wx). The resulting F₁ plants were crossed to pure-breeding colorless, shrunken, starchy plants. Counting the kernels from about 30 ears of corn yields the following data.

Kernel Phenotype                           Number
Colored, shrunken, starchy               116
Colored, full, waxy                             601
Colored, full, starchy                        2538
Colored, shrunken, waxy                       4
Colorless, shrunken, starchy            2708
Colorless, full, starchy                            2
Colorless, full, waxy                            113
Colorless, shrunken, waxy                  626
                                                          6708

Calculate the recombination frequencies between the gene pairs.

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.

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 independent assortment among any of these gene pairs? If so, identify the evidence.

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

Using the gene symbols given above, write the genotypes of F₁ and F₂ plants.

The table given here lists the arrangement of alleles of linked genes in dihybrid organisms, the recombination frequency between the genes, and specific gamete genotypes. Using the information provided, determine the expected frequency of the listed gametes. Assume one map unit equals 1% recombination and, when three genes are involved, interference is zero.

Dihybrid           Recombination         Gamete
Genotype         Frequency                Genotype
A. DE/de           8%                           De
B. AD/ad           28%                          ad
C. DEF/def        E–F 24%                  dEf
                          D–E 8%
D. BdE/bDe       B–D 18%                 Bde
                          D–E 8%

The Rh blood group in humans is determined by a gene on chromosome 1. A dominant allele produces Rh+ blood type, and a recessive allele generates Rh-. Elliptocytosis is an autosomal dominant disorder that produces abnormally shaped red blood cells that have a short life span resulting in hereditary anemia. A large family with elliptocytosis is tested for genetic linkage of Rh blood group and the disease. The lod score data below are obtained for the family.

From these data, can you conclude that Rh and elliptocytosis loci are genetically linked in this family? Why or why not?

The Rh blood group in humans is determined by a gene on chromosome 1. A dominant allele produces Rh+ blood type, and a recessive allele generates Rh-. Elliptocytosis is an autosomal dominant disorder that produces abnormally shaped red blood cells that have a short life span resulting in hereditary anemia. A large family with elliptocytosis is tested for genetic linkage of Rh blood group and the disease. The lod score data below are obtained for the family.

What is Zₘₐₓ for this family? 

The Rh blood group in humans is determined by a gene on chromosome 1. A dominant allele produces Rh+ blood type, and a recessive allele generates Rh-. Elliptocytosis is an autosomal dominant disorder that produces abnormally shaped red blood cells that have a short life span resulting in hereditary anemia. A large family with elliptocytosis is tested for genetic linkage of Rh blood group and the disease. The lod score data below are obtained for the family.

Over what range of θ do lod scores indicate significant evidence in favor of genetic linkage? <>