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Ch. 5 - Genetic Linkage and Mapping in Eukaryotes
Sanders - Genetic Analysis: An Integrated Approach 3rd Edition
Sanders3rd EditionGenetic Analysis: An Integrated ApproachISBN: 9780135564172Non è quello che usi tu?Cambia libro di testo
Capitolo 5, Problema 25b

In rabbits, chocolate-colored fur (w⁺) is dominant to white fur (w), straight fur (c⁺) is dominant to curly fur (c), and long ear (s⁺) is dominant to short ear (s). The cross of a trihybrid rabbit with straight, chocolate-colored fur and long ears to a rabbit that has white, curly fur and short ears produces the following results:
Table displaying phenotypes and their corresponding numbers for a trihybrid rabbit cross.
Calculate the recombination frequencies between each of the adjacent pairs of genes.

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Step 1: Identify the parental phenotypes and recombinant phenotypes. Parental phenotypes are those that match the phenotypes of the parents in the cross. In this case, the parental phenotypes are 'Chocolate, long, straight' and 'White, short, curly'. Recombinant phenotypes are all other combinations of traits.
Step 2: Group the phenotypes based on the traits being analyzed. For example, to calculate the recombination frequency between fur color (w⁺/w) and fur texture (c⁺/c), group the phenotypes based on these traits. Similarly, do this for fur texture and ear length (c⁺/c and s⁺/s), and fur color and ear length (w⁺/w and s⁺/s).
Step 3: Count the number of recombinant offspring for each pair of traits. Recombinant offspring are those that do not match the parental combinations for the traits being analyzed. For example, for fur color and fur texture, count the offspring with 'Chocolate, curly' and 'White, straight' phenotypes.
Step 4: Calculate the recombination frequency for each pair of traits using the formula: Number⁣of⁣recombinant⁣offspringTotal⁣number⁣of⁣offspring. Multiply the result by 100 to express it as a percentage.
Step 5: Repeat the calculation for each pair of traits (fur color and fur texture, fur texture and ear length, fur color and ear length) to determine the recombination frequencies between adjacent pairs of genes.

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Dominance and Alleles

In genetics, dominance refers to the relationship between alleles, where one allele (dominant) masks the expression of another (recessive). In this case, chocolate-colored fur (w⁺) is dominant over white fur (w), straight fur (c⁺) is dominant over curly fur (c), and long ears (s⁺) are dominant over short ears (s). Understanding these relationships is crucial for predicting phenotypes in offspring based on parental genotypes.
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Variations on Dominance

Punnett Squares and Genetic Crosses

Punnett squares are tools used to predict the genotypic and phenotypic outcomes of genetic crosses. In this scenario, a trihybrid cross involves three traits, and the Punnett square can help visualize the combinations of alleles from the parents. By analyzing the offspring's phenotypes, one can infer the underlying genotypes and calculate the expected ratios of each phenotype.
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Recombination Frequency

Recombination frequency is a measure of the likelihood that two genes will be separated during meiosis due to crossing over. It is calculated by determining the proportion of recombinant offspring to the total number of offspring. This concept is essential for understanding genetic linkage and mapping genes on chromosomes, as it helps to identify how closely genes are located to each other.
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03:51
Recombination after Single Strand Breaks
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Domanda del libro di testo

The following progeny are obtained from a test cross of a trihybrid wild-type plant to a plant with the recessive phenotypes compound leaves (c), intercalary leaflets (i), and green fruits (g). (Traits not listed are wild type.) The test-cross progeny are as follows:

Determine the order of the three genes, and construct a genetic map that identifies the correct order and the alleles carried on each chromosome in the trihybrid parental plant.

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The boss in your laboratory has just heard of a proposal by another laboratory that genes for eye color and the length of body bristles may be linked in Drosophila. Your lab has numerous pure-breeding stocks of Drosophila that could be used to verify or refute genetic linkage. In Drosophila, red eyes (c⁺) are dominant to brown eyes (c) and long bristles (d⁺) are dominant to short bristles (d). Your lab boss asks you to design an experiment to test the genetic linkage of eye color and bristle-length genes, and to begin by crossing a pure-breeding line homozygous for red eyes and short bristles to a pure-breeding line that has brown eyes and long bristles.


How would the results of the cross differ if the genes are not linked?

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Domanda del libro di testo

In rabbits, chocolate-colored fur (w⁺) is dominant to white fur (w), straight fur (c⁺) is dominant to curly fur (c), and long ear (s⁺) is dominant to short ear (s). The cross of a trihybrid rabbit with straight, chocolate-colored fur and long ears to a rabbit that has white, curly fur and short ears produces the following results:

Determine the interference value for this cross.

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The following progeny are obtained from a test cross of a trihybrid wild-type plant to a plant with the recessive phenotypes compound leaves (c), intercalary leaflets (i), and green fruits (g). (Traits not listed are wild type.) The test-cross progeny are as follows:

Calculate the frequencies of recombination between the adjacent genes in the map.

447
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Domanda del libro di testo

The boss in your laboratory has just heard of a proposal by another laboratory that genes for eye color and the length of body bristles may be linked in Drosophila. Your lab has numerous pure-breeding stocks of Drosophila that could be used to verify or refute genetic linkage. In Drosophila, red eyes (c⁺) are dominant to brown eyes (c) and long bristles (d⁺) are dominant to short bristles (d). Your lab boss asks you to design an experiment to test the genetic linkage of eye color and bristle-length genes, and to begin by crossing a pure-breeding line homozygous for red eyes and short bristles to a pure-breeding line that has brown eyes and long bristles.


Assume the eye color and bristle-length genes are separated by 28 m.u. What are the approximate frequencies of phenotypes expected from the cross you proposed in part (b)?

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Domanda del libro di testo

In rabbits, chocolate-colored fur (w⁺) is dominant to white fur (w), straight fur (c⁺) is dominant to curly fur (c), and long ear (s⁺) is dominant to short ear (s). The cross of a trihybrid rabbit with straight, chocolate-colored fur and long ears to a rabbit that has white, curly fur and short ears produces the following results:

Determine the order of the genes on the chromosome, and identify the alleles that are present on each of the homologous chromosomes in the trihybrid rabbits.

447
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