8.In the snail Cepaea nemoralis, an autosomal allele causing a banded shell (B^B) is recessive to the allele for an unbanded shell (B^O). Genes at a different locus determine the background color of the shell; here, yellow (C^Y) is recessive to brown (C^Bw). A banded, yellow snail is crossed with a homozygous brown, unbanded snail. The F₁ are then crossed with banded, yellow snails (a testcross).

*9.In silkmoths (Bombyx mori), red eyes (re) and white-banded wings (wb) are encoded by two mutant alleles that are recessive to those that produce wild-type traits (re⁺ and wb⁺); these two genes are on the same chromosome. A moth homozygous for red eyes and white-banded wings is crossed with a moth homozygous for the wild-type traits. The F₁ have normal eyes and normal wings. The F₁ are crossed with moths that have red eyes and white-banded wings in a testcross. The progeny of this testcross are

*10.A geneticist discovers a new mutation in Drosophila melanogaster that causes the flies to shake and quiver. She calls this mutation spastic (sps) and determines that it is due to an autosomal recessive gene. She wants to determine whether the gene encoding spastic is linked to the recessive gene for vestigial wings (vg). She crosses a fly homozygous for spastic and vestigial traits with a fly homozygous for the wild-type traits and then uses the resulting F₁ females in a testcross. She obtains the following flies from this testcross:

Are the genes that cause vestigial wings and spastic linked? Do a chi-square test of independence to determine whether the genes have assorted independently.

*11.In cucumbers, heart-shaped leaves (hl) are recessive to normal leaves (Hl) and numerous fruit spines (ns) are recessive to few fruit spines (Ns). The genes for leaf shape and for number of spines are located on the same chromosome; findings from mapping experiments indicate that they are 32.6 m.u. apart. A cucumber plant having heart-shaped leaves and numerous spines is crossed with a plant that is homozygous for normal leaves and few spines. The F₁ are crossed with plants that have heart-shaped leaves and numerous spines. What phenotypes and phenotypic proportions are expected in the progeny of this cross?

12.In tomatoes, tall (D) is dominant over dwarf (d), and smooth fruit (P) is dominant over pubescent fruit (p), which is covered with fine hairs. A farmer has two tall and smooth tomato plants, which we will call plant A and plant B. The farmer crosses plants A and B with the same dwarf and pubescent plant and obtains the following numbers of progeny:

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13.Alleles A and a are at a locus on the same chromosome as is a locus with alleles B and b. Aa Bb is crossed with aa bb and the following progeny are produced:

What conclusion can be made about the arrangement of the genes on the chromosome in the Aa Bb parent?

14.Recombination frequencies between three loci in corn are shown here.

What is the order of the genes on the chromosome?

15.In German cockroaches, bulging eyes (bu) are recessive to normal eyes (bu⁺), and curved wings (cv) are recessive to straight wings (cv⁺). Both traits are encoded by autosomal genes that are linked. A cockroach has genotype bu⁺bu cv⁺cv and the genes are in repulsion. Which of the following sets of genes will be found in the most common gametes produced by this cockroach?

Explain your answer.

*16.In Drosophila melanogaster, ebony body (e) and rough eyes (ro) are encoded by autosomal recessive genes found on chromosome 3; they are separated by 20 m.u. The gene that encodes forked bristles (f) is X-linked recessive and assorts independently of e and ro. Give the phenotypes of progeny and their expected proportions when a female of each of the following genotypes is test-crossed with a male.

17.Perform a chi-square test of independence on the data provided in Figure 5.2 to determine if the genes for flower color and pollen shape in sweet peas are assorting independently. Give the chi-square value, degrees of freedom, and associated probability. What conclusion would you make about the independent assortment of these genes?

*18.A series of two-point crosses were carried out among seven loci (a, b, c, d, e, f, and g), producing the following recombination frequencies. Map the seven loci, showing their linkage groups, the order of the loci in each linkage group, and the distances between the loci of each group.

19. R. W. Allard and W. M. Clement determined recombination rates for a series of genes in lima beans (R. W. Allard and W. M. Clement. 1959. Journal of Heredity 50:63–67). The following table lists paired recombination frequencies for eight of the loci (D, Wl, R, S, L₁, Ms, C, and G) that they mapped. On the basis of these data, draw a series of genetic maps for the different linkage groups of the genes, indicating the distances between the genes. Keep in mind that these frequencies are estimates of the true recombination frequencies and that some error is associated with each estimate. An asterisk beside a recombination frequency indicates that the recombination frequency is significantly different from 50%.

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* Significantly different from 50%

*20.Waxy endosperm (wx), shrunken endosperm (sh), and yellow seedlings (v) are encoded by three recessive genes in corn that are linked on chromosome 5. A corn plant homozygous for all three recessive alleles is crossed with a plant homozygous for all the dominant alleles. The resulting F₁ are then crossed with a plant homozygous for the recessive alleles in a three-point testcross. The progeny of the testcross are

21. Priscilla Lane and Margaret Green studied the linkage relations of three genes affecting coat color in mice: mahogany (mg), agouti (a), and ragged (Rg). They carried out a series of three-point crosses, mating mice that were heterozygous at all three loci with mice that were homozygous for the recessive alleles at these loci (P W. Lane and M. C. Green. 1960. Journal of Heredity 51:228–230). The following table lists the progeny of the testcrosses:

Note: + represents a wild-type allele.

22. Fine spines (s), smooth fruit (tu), and uniform fruit color (u) are three recessive traits in cucumbers, the genes for which are linked on the same chromosome. A cucumber plant heterozygous for all three traits is used in a testcross, and the following progeny are produced by this testcross:

*23.Raymond Popp studied linkage among genes for pink eye (p), shaker-1 (sh-1, which causes circling behavior, head tossing, and deafness), and hemoglobin (Hb) in mice (R. A. Popp. 1962. Journal of Heredity 53:73–80). He performed a series of testcrosses, in which mice heterozygous for pink eye, shaker-1, and hemoglobin 1 and 2 were crossed with mice that were homozygous for pink eye, shaker-1, and hemoglobin 2.

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The following progeny were produced:

*24.In Drosophila melanogaster, black body (b) is recessive to gray body (b⁺), purple eyes (pr) are recessive to red eyes (pr⁺), and vestigial wings (vg) are recessive to normal wings (vg⁺). The loci encoding these traits are linked, with the following map distances:

The interference among these genes is 0.5. A fly with a black body, purple eyes, and vestigial wings is crossed with a fly homozygous for a gray body, red eyes, and normal wings. The female progeny are then crossed with males that have a black body, purple eyes, and vestigial wings. If 1000 progeny are produced by this testcross, what will be the phenotypes and proportions of the progeny?

25.Sepia eyes, spineless bristles, and striped thorax are three recessive mutations in Drosophila found on chromosome 3. A genetics student crosses a fly homozygous for sepia eyes, spineless bristles, and striped thorax with a fly homozygous for the wild-type traits—red eyes, normal bristles, and solid thorax. The female progeny are then test-crossed with males that have sepia eyes, spineless bristles, and striped thorax. Assume that the interference between these genes is 0.2 and that 400 progeny flies are produced by the testcross. Based on the map distances provided in Figure 5.14, predict the phenotypes and proportions of the progeny resulting from the testcross.

26.Eight DNA sequences from different individuals are given in the diagram below.