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Ch. 4 - Modification of Mendelian Ratios
Klug - Essentials of Genetics 10th Edition
Klug10th EditionEssentials of GeneticsISBN: 9780135588789당신이 사용하는 게 아니라요?교과서 변경
4장, 문제 18a

A geneticist from an alien planet that prohibits genetic research brought with him to Earth two pure-breeding lines of frogs. One line croaks by uttering 'rib-it rib-it' and has purple eyes. The other line croaks more softly by muttering 'knee-deep knee-deep' and has green eyes. With a newfound freedom of inquiry, the geneticist mated the two types of frogs, producing F₁ frogs that were all utterers and had blue eyes. A large F₂ generation then yielded the following ratios:
27/64 blue-eyed, 'rib-it' utterer
12/64 green-eyed, 'rib-it' utterer
9/64 blue-eyed, 'knee-deep' mutterer
9/64 purple-eyed, 'rib-it' utterer
4/64 green-eyed, 'knee-deep' mutterer
3/64 purple-eyed, 'knee-deep' mutterer
How many total gene pairs are involved in the inheritance of both traits? Support your answer.

검증된 단계별 안내
1
Step 1: Identify the phenotypes and their ratios in the F₂ generation and recognize that the traits are likely controlled by multiple gene pairs. The traits are eye color (purple, blue, green) and croaking sound ('rib-it' vs. 'knee-deep'). The F₁ generation is uniform with blue eyes and 'rib-it' croaking, indicating dominance patterns.
Step 2: Analyze the F₂ phenotypic ratios given: 27/64, 12/64, 9/64, 9/64, 4/64, and 3/64. Notice that the denominators are all 64, which is a clue that the total number of gene pairs involved is related to the number of possible genotype combinations, since \(2^n = 64\) implies \(n=6\) gene pairs if each gene is independently assorting with two alleles.
Step 3: Consider that each gene pair segregates independently and contributes to the phenotypic ratios. The total number of genotypic combinations for \(n\) gene pairs is \$2^{2n}$, but since each gene pair has two alleles, the number of phenotypic classes in a dihybrid cross is \$4^n$. Here, the denominator 64 suggests \(4^n = 64\), so solve for $n$ by setting \(4^n = 64\).
Step 4: Calculate \(n\) by taking logarithms: \(n = \log_4 64\). Since \(4^3 = 64\), this means \(n=3\). Therefore, three gene pairs are involved in the inheritance of both traits combined.
Step 5: Support this conclusion by explaining that the observed phenotypic ratios correspond to a trihybrid cross (three gene pairs), where each gene pair contributes to the traits of eye color and croaking sound, and the F₂ ratios reflect the independent assortment and combination of these gene pairs.

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이 영상 해법은 위 문제에 도움이 된다고 튜터들이 추천한 것입니다.
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주요 개념

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Dihybrid and Multihybrid Crosses

Dihybrid and multihybrid crosses involve tracking inheritance of two or more gene pairs simultaneously. The phenotypic ratios in offspring reflect the number of gene pairs and their independent assortment. For example, a typical dihybrid cross yields a 9:3:3:1 ratio, while more gene pairs produce more complex ratios based on 4^n total phenotypic classes.
추천 영상:

Mendelian Ratios and Probability

Mendelian genetics predicts offspring ratios based on dominant and recessive alleles segregating independently. The total number of phenotypic classes is 4^n for n gene pairs with two alleles each. Observed ratios can be compared to expected ratios to deduce the number of gene pairs controlling traits.
추천 영상:

Phenotypic Classification and Gene Interaction

Phenotypes result from combinations of alleles at different loci. Each gene pair can influence distinct traits, and their combinations produce unique phenotypes. Understanding how to classify phenotypes by traits and their ratios helps infer the number of gene pairs involved in inheritance.
추천 영상:
가이드 코스
07:56
Interacting Genes Overview
관련 실천
교과서 질문

A geneticist from an alien planet that prohibits genetic research brought with him to Earth two pure-breeding lines of frogs. One line croaks by uttering 'rib-it rib-it' and has purple eyes. The other line croaks more softly by muttering 'knee-deep knee-deep' and has green eyes. With a newfound freedom of inquiry, the geneticist mated the two types of frogs, producing F₁ frogs that were all utterers and had blue eyes. A large F₂ generation then yielded the following ratios:

27/64 blue-eyed, 'rib-it' utterer

12/64 green-eyed, 'rib-it' utterer

9/64 blue-eyed, 'knee-deep' mutterer

9/64 purple-eyed, 'rib-it' utterer

4/64 green-eyed, 'knee-deep' mutterer

3/64 purple-eyed, 'knee-deep' mutterer

Indicate the genotypes of the six F₂ phenotypes.

460
views
교과서 질문

While vermilion is X-linked in Drosophila and causes the eye color to be bright red, brown is an autosomal recessive mutation that causes the eye to be brown. Flies carrying both mutations lose all pigmentation and are white-eyed. Predict the F₁ and F₂ results of the following crosses:

white females x wild-type males

1886
views
교과서 질문

A geneticist from an alien planet that prohibits genetic research brought with him to Earth two pure-breeding lines of frogs. One line croaks by uttering 'rib-it rib-it' and has purple eyes. The other line croaks more softly by muttering 'knee-deep knee-deep' and has green eyes. With a newfound freedom of inquiry, the geneticist mated the two types of frogs, producing F₁ frogs that were all utterers and had blue eyes. A large F₂ generation then yielded the following ratios:

27/64 blue-eyed, 'rib-it' utterer

12/64 green-eyed, 'rib-it' utterer

9/64 blue-eyed, 'knee-deep' mutterer

9/64 purple-eyed, 'rib-it' utterer

4/64 green-eyed, 'knee-deep' mutterer

3/64 purple-eyed, 'knee-deep' mutterer

Of these, how many are controlling eye color? How can you tell? How many are controlling croaking?

578
views
교과서 질문

While vermilion is X-linked in Drosophila and causes the eye color to be bright red, brown is an autosomal recessive mutation that causes the eye to be brown. Flies carrying both mutations lose all pigmentation and are white-eyed. Predict the F₁ and F₂ results of the following crosses:

brown females x vermilion males

1640
views
교과서 질문

A geneticist from an alien planet that prohibits genetic research brought with him to Earth two pure-breeding lines of frogs. One line croaks by uttering 'rib-it rib-it' and has purple eyes. The other line croaks more softly by muttering 'knee-deep knee-deep' and has green eyes. With a newfound freedom of inquiry, the geneticist mated the two types of frogs, producing F₁ frogs that were all utterers and had blue eyes. A large F₂ generation then yielded the following ratios:

27/64 blue-eyed, 'rib-it' utterer

12/64 green-eyed, 'rib-it' utterer

9/64 blue-eyed, 'knee-deep' mutterer

9/64 purple-eyed, 'rib-it' utterer

4/64 green-eyed, 'knee-deep' mutterer

3/64 purple-eyed, 'knee-deep' mutterer

Assign gene symbols for all phenotypes and indicate the genotypes of the P₁ and F₁ frogs.

508
views