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1) Ants are haplodiploid organisms. This means females are diploid (2n) and males are haploid (n). The gametes produced by both males and females are haploid (n). There is no homologous recombination in males during gamete formation. There is no sex chromosome. In an ant species, it is known that wings formation (F) and setae density (D) are each controlled by a different, simple-Mendelian locus/gene. Individuals which are homozygous recessive for both genes have no wings (f) and no setae (d). Previous experiments also indicated that both loci/genes are on the same chromosome.

a. Design a test cross to map the genetic distance of the genes, by writing the genotype of the tester and its mate. (2 pts) Genotype of tester: Genotype of tester’s mate:

b. In order for the test cross to produce offspring with non-parental phenotypes, the tester has to be of a specific sex. What sex must the tester be? Briefly explain your choice in your own words. (Hint: what is a test cross?) (2 pts) Sex of tester:

c. 100 offspring were produced from a particular test cross. The phenotypic ratio of these offspring is observed to be the following:

Normal wings and setae density40

Wings and setae both absent 47

Normal wings but no setae 4

Normal setae density but no wings 9

Calculate and describe in words the genetic distance between the two loci/genes of interest. Remember to include the unit of measurement (6 pts).

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Beverley Smith
Beverley SmithLv2
28 Sep 2019

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Related questions

Drosophila has four pairs of chromosomes: the sex chromosomes (XX in the females; XY in the males) and three pairs of autosomes. You are studying a new mutant strain with blue eyes. You wish to know if blue eye colour is a dominant mutation and on which chromosome the blue eye locus can be found. When you cross a pure-breeding female blue-eyed fly with vestigial wings and spineless bristles to a male fly with wild type eye colour, wings, and bristles, all of the F1 progeny are completely wild type. An F1 male is backcrossed to a triple mutant female, producing the following progeny (remember that there is no crossing over in Drosophila males):

Wild type eyes, wings, and bristles:

72 females, 69 males

Wild type eyes and bristles, vestigial:

83 females, 77 males

Wild type wings, blue eyes, spineless:

60 females, 65 males

Blue eyes, spineless, vestigial:

62 females, 58 males

a. Is the mutation dominant or recessive? Explain.

b. Since you know that the locus for vestigial wings is on chromosome 2 and the locus for spineless bristles is on chromosome 3, what chromosome carries the locus for blue eyes? Show your work, including the step-by-step reasoning you used to arrive at your answer.

c. When an F1 female is backcrossed to a triple mutant male, the following 1,000 progeny are produced:

Wild type eyes, wings, and bristles:

90 females, 89 males

Wild type eyes and bristles, vestigial:

83 females, 98 males

Wild type eyes and wings, spineless:

37 females, 35 males

Wild type wings and bristles, blue eyes:

36 females, 34 males

Wild type wings, blue eyes, spineless:

92 females, 88 males

Wild type eyes, spineless, vestigial:

34 females, 39 males

Wild type bristles, vestigial, blue eyes:

33 females, 37 males

Blue eyes, spineless, vestigial:

90 females, 85 males

Calculate the map distance between blue eye and any linked genes. Show your work.

2) Consider a haploid male of a certain ant species. This male’s karyotype contains a total of 3 nonhomologous chromosomes. It was estimated that the genome of this ant species contains approximately 12,000 protein-coding genes.

a. Assuming genes are distributed evenly across chromosomes, on average how many genes do you expected to find on a given chromosome of this male ant? (2 pts)

b. What is the number of allele the male ant have for each of its gene? Briefly explain your answer in your own words. (2 pts)

c. What types of gametes can this male produce (e.g. recombinant, non-recombinant, or both)? Briefly explain your answer in your own words. (3 pts)

d. In this species, previous experiments indicated that two genes, A and B, have a recombination frequency of 23%. You want to verify this statistics by conducting your own test cross experiment. Describe in a complete sentence the expected phenotypic ratio of the offspring from a test cross for these two genes, given the statistics. Mention recombinant and parental phenotypes. (3 pts)

Under the Hardy-Weinberg model, a population will reach Hardy-Weinberg frequencies in a single generation. This model assumes that genotype frequencies are the same in both sexes: Consider a situation where this is not the case. A researcher creates a new Drosophila population by selecting 2000 males from a stock population fixed for the dominant A allele at a neutral locus A and 2000 females from a different stock population fixed for the recessive a allele at the A locus. The A allele is located on an autosome, not a sex chromosome. These individuals then mate among themselves.

a) Assuming that there is no mutation, what genotype frequencies will be observed in the first offspring generation?

b) How long will it take this population to reach Hardy-Weinberg proportions?

c) Explain why this population took two generations instead of one to reach Hardy-Weinberg equilibrium.

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