Crossing Over and Recombinants Practice Problems

In an experiment, researchers are studying two genes in mice that control fur color and eye color. The genes are located on the same chromosome, and the alleles for the genes are as follows:

Gene 1: Black fur (B) is dominant to brown fur (b)
Gene 2: Red eyes (R) are dominant to black eyes (r)

In the F1 generation of a cross between two pure-breeding parents (BBRR x bbrr), all the offspring had black fur and red eyes. The F1 mice were then crossed with bbrr mice to produce the F2 generation.

Out of 100 F2 mice, the researchers observed the following phenotypes:

Black fur, red eyes: 48
Black fur, black eyes: 16
Brown fur, red eyes: 20
Brown fur, black eyes: 16

What is the recombination frequency between the two genes?

In a study of the inheritance of two genes in pea plants, a researcher crossed a pure-breeding plant with yellow, round seeds (YYRR) to a pure-breeding plant with green, wrinkled seeds (yyrr). All of the F₁ offspring had yellow, round seeds (YyRr). The researcher then crossed the F₁ to each other to produce an F₂ generation.

The results of the F₂ generation are as follows:

Phenotype Number
Yellow, round 602
Yellow, wrinkled 191
Green, round 202
Green, wrinkled 605
Total 1600

Using the chi-square test, which of the following statements can be true?

In a genetic study of peas, a researcher is interested in two traits: seed color (yellow is dominant to green) and seed shape (round is dominant to wrinkled). The researcher starts with two pure-breeding pea plants: one with yellow, round seeds (YYRR) and the other with green, wrinkled seeds (yyrr). The researcher performs a dihybrid cross between the two plants and obtains F₁ progeny that are all yellow and round (YyRr).

The researcher then crosses the F₁ progeny to a pure-breeding pea plant with green, wrinkled seeds (yyrr) and obtains the following F₂ progeny:

Phenotype Number

Yellow, round 183

Yellow, wrinkled 20

Green, round 5

Green, wrinkled 192

Total 400

Considering the given data, the recombination frequency between the gene for seed color and the gene for seed shape is:

In experiments published in 1933, Barbara McClintock studied potential genetic linkage in corn (Zea mays) for genes controlling kernel color (colored is dominant to colorless) and endosperm composition (starchy is dominant to sugary). McClintock performed two crosses. In the first cross, pure-breeding colored (CC), starchy-kernel (SS) plants were crossed to plants pure-breeding for colorless (cc), sugary (ss) kernels. The F₁ of this cross were test-crossed to colorless (cc), and sugary (ss) plants. The test-cross progeny were as follows:

Phenotype Number
Colored, starchy 731
Colorless, sugary 714
Colored, sugary 28
Colorless, starchy 9
Total 1482

Considering the given data, which of the following statements is therefore true?

In guinea pigs, the allele for short hair (S) is dominant over the allele for long hair (s), and the allele for white color (W) is dominant over the allele for black color (w). We then cross a guinea pig that is heterozygous for both traits with a tester and they produce the following offspring:

with parental configuration 1: 45
with parental configuration 2: 51
recombinant 1: 15
recombinant 2: 10

The offspring will have the following genotypes except:

In guinea pigs, the allele for short hair (S) is dominant over the allele for long hair (s), and the allele for white color (W) is dominant over the allele for black color (w). We then cross a guinea pig that is heterozygous for both traits with a tester and they produce the following offspring:

with parental configuration 1: 45
with parental configuration 2: 51
recombinant 1: 15
recombinant 2: 10

What does this tell us in terms of genetic linkage?

In guinea pigs, the allele for short hair (S) is dominant over the allele for long hair (s), and the allele for white color (W) is dominant over the allele for black color (w). We then cross a guinea pig that is heterozygous for both traits with a tester and they produce the following offspring:

with parental configuration: 45
recombinants: 15

What is the recombination frequency?

Suppose we study the genetic linkage of two genes in peas. To determine the genetic linkage, we cross a wild-type pea with a mutant pea and obtain offspring with parental configurations and recombinants. We then conducted a test cross in the F1 progeny and obtained another set of offspring (F2). Using the chi-square test, we determined that the genes are not linked. Suppose we used linked genes, what can we expect in the computed P-value after conducting the chi-square test?

Consider that there are five genes p, q, x, y, z. Determine the sequence of genes on the chromosomes if the cross-over percentage between linked genes is as follows:
1) p and y = 25%, 2) p and z = 15%, 3) p and q = 15%, 4) y and x = 10%, 5) z and q = 30%, 6) z and y = 10%. 

In cross-over studies on maize, the following percentage of genes X, Y, Z, and W crossed over: between X and W 15%, between X and Z 4%, between genes Z and W 11%, between genes X and Y 6%, and between genes Z and Y 10% respectively. Therefore the correct sequence of genes X, Y, Z, and W on the chromosome is:

Gene mapping is the process of determining the location of genes on chromosomes. Recombination between linked genes can be used to map their distance apart on the chromosome. What is the distance between the two genes if 15% of the gametes produced by meiosis are recombinant?

We observed in the garden that green-seeded (G) peas are dominant over yellow-seeded (g) peas and purple-flowered (P) peas are dominant over white-flowered (p) peas. We conducted an experiment by crossing the dominant true-breeding peas and recessive true-breeding peas and obtained heterozygous offspring. After obtaining the F1 dihybrid, we conducted a test cross by crossing the F1 dihybrid in a recessive true-breeding pea. We then obtain a total of 135 recombinants out of 520 offspring in the F2 progeny. Using these values, what is the distance between gene G and gene P?

At the ____________ stage of prophase-I, non-sister chromatids of the ____________ chromosome cross over.

We observed in the garden that green-seeded (G) peas are dominant over yellow-seeded (g) peas and purple-flowered (P) peas are dominant over white-flowered (p) peas. We conducted an experiment by crossing the dominant true-breeding peas and recessive true-breeding peas and obtained heterozygous offspring. Which of the following genotypes can we use to cross with the F1 dihybrid to determine the genetic linkage of the two genes?

We observed in the garden that green-seeded (G) peas are dominant over yellow-seeded (g) peas and purple-flowered (P) peas are dominant over white-flowered (p) peas. If we cross dominant true-breeding peas and recessive true-breeding peas, what will be the genotype of the offspring in the F1 progeny?

If genes B and D are perfectly unlinked with each other, what is their possible recombination frequency value after meiotic cell division?

Suppose two genes are located in the same chromosome and they undergo crossing over with another homologous chromosome. If the frequency of gametes containing alleles in the parental configuration is 48% each and the frequency of gametes containing recombinant configuration is 2% each, which of the following conclusions is therefore true?

The process that occurs during meiosis in which homologous chromosomes exchange genetic material and can lead to the separation of alleles of different genes that are on the same chromosome is:

Suppose genes B and C are very close together on the same chromosome. What can we expect from the gametes formed after meiotic cell division?

The genes for purple eye (p) and vestigial wing (vg) are 10.7 m.u. apart. The following cross was done in Drosophila: p⁺vg⁺/pvg  x  pvg/pvg, and 1000 offspring were obtained. Calculate the total number of recombinant offspring.

If you want to detect recombinant offspring in Drosophila, what should the genotypes of the female and male parents be?

The genes for short artisae (s), black body (b) and brown eyes (bw) are present on chromosome 2 of Drosophila. The order of these genes are as follows: s–b–bw. Identify which of the following gametes is not a result of a single crossover in a female with the sbbw⁺/s⁺b⁺bw genotype.

In Drosophila, crossing over was shown to occur only in females and not in males. The gene for purple eyes and vestigial wing are 10.7 m.u. apart on chromosome 2 .Determine the number of gametes produced by a female and male Drosophila, both of which have genotypes p⁺/p vg⁺/vg.

It has been observed that in the maize cross, only 7.8% of the double crossovers are observed, compared to an expected 9.7%. Which of the following phenomena is responsible for such an observation?

Two genes that are very close on a chromosome will show:

What is the structure that is formed between dyads during crossing over?

Which of the following best explains why genes on the same chromosome are not always inherited together?

The genes responsible for controlling the blood group systems are located on the autosomes. However, Xg blood group alleles are located in _______.

Which of the following statements is true about linked genes?

The process by which sections of a homologous chromosome are physically broken and rejoined is called:

_______ refers to the stained paired sister chromatids to reveal the sister chromatid exchanges.