4. Genetic Mapping and Linkage

Crossing Over and Recombinants

4. Genetic Mapping and Linkage

Crossing Over and Recombinants

Struggling with Genetics?

Join thousands of students who trust us to help them ace their exams!Watch the first video

2:54 minutes

Open Question

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.

Verified video answer for a similar problem:

This video solution was recommended by our tutors as helpful for the problem above

Video duration:

Was this helpful?

7:52m

Watch next

Master Gamete Genotypes with a bite sized video explanation from Kylia

Start learning

Related Videos

Related Practice

Open Question

In laboratory class, a genetics student was assigned to study an unknown mutation in Drosophila that had a whitish eye. He crossed females from his true-breeding mutant stock to wild-type (brick-red-eyed) males, recovering all wild-type F₁ flies. In the F₂ generation, the following offspring were recovered in the following proportions:wild type 5/8bright red 1/8brown eye 1/8white eye 1/8The student was stumped until the instructor suggested that perhaps the whitish eye in the original stock was the result of homozygosity for a mutation causing brown eyes and a mutation causing bright red eyes, illustrating gene interaction (see Chapter 4). After much thought, the student was able to analyze the data, explain the results, and learn several things about the location of the two genes relative to one another. One key to his understanding was that crossing over occurs in Drosophila females but not in males. Based on his analysis, what did the student learn about the two genes?

Open Question

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.

Open Question

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.

Open Question

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.

Open Question

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.

Open Question

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.

Multiple Choice

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

Multiple Choice

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?

Show more practices

Crossing Over and Recombinants practice set

Problem sets built by lead tutors

Expert video explanations

Go to Practice