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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: 9780135564172당신이 사용하는 게 아니라요?교과서 변경
5장, 문제 5a

In tomato plants, purple leaf color is controlled by a dominant allele A, and green leaf by a recessive allele a. At another locus, hairy leaf H is dominant to hairless leaf h. The genes for leaf color and leaf texture are separated by 16 m.u. on chromosome 5. On chromosome 4, a gene controlling leaf shape has two alleles: a dominant allele C that produces cut-leaf shape and a recessive allele c that produces potato-shaped leaves.
The cross of a purple, hairy, cut plant heterozygous at each gene to a green, hairless potato plant produces the following progeny:
 Table displaying phenotypes of tomato plant progeny and their frequency percentages.
Give the genotypes of parental and progeny plants in this experiment.

검증된 단계별 안내
1
Step 1: Identify the parental genotypes. The problem states that the purple, hairy, cut plant is heterozygous at each gene, so its genotype is AaHhCc. The green, hairless, potato plant is homozygous recessive for all traits, so its genotype is aahhcc.
Step 2: Determine the possible gametes for each parent. The heterozygous parent (AaHhCc) can produce 8 types of gametes (AHC, AHc, AhC, Ahc, aHC, aHc, ahC, ahc) due to independent assortment. The homozygous recessive parent (aahhcc) can only produce one type of gamete (ahc).
Step 3: Analyze the progeny phenotypes and frequencies. The progeny phenotypes and their frequencies suggest that the genes A and H are linked, as the parental phenotypes (purple, hairy, cut and green, hairless, potato) are more frequent (21% each) than the recombinant phenotypes (e.g., purple, hairless, cut at 4%).
Step 4: Use the recombination frequency to confirm linkage. The recombination frequency between A and H is given as 16 m.u. (map units), which corresponds to 16% recombination. This matches the sum of the recombinant phenotypes (4% + 4% + 4% + 4% = 16%).
Step 5: Assign genotypes to the progeny. For each phenotype, deduce the genotype based on the traits: (1) Purple, hairy, cut = AaHhCc, (2) Purple, hairy, potato = AaHhcc, (3) Green, hairless, cut = aahhCc, (4) Green, hairless, potato = aahhcc, (5) Purple, hairless, cut = AaHhCc (recombinant), (6) Purple, hairless, potato = AaHhcc (recombinant), (7) Green, hairy, cut = aahhCc (recombinant), (8) Green, hairy, potato = aahhcc (recombinant).

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주요 개념

질문에 올바르게 답하기 위해 반드시 이해해야 하는 핵심 개념들은 다음과 같습니다.

Dominant and Recessive Alleles

In genetics, alleles are different forms of a gene that can exist at a specific locus on a chromosome. Dominant alleles, represented by uppercase letters (e.g., A, H, C), mask the expression of recessive alleles, represented by lowercase letters (e.g., a, h, c). In this question, the purple leaf color (A) is dominant over green (a), and hairy leaves (H) are dominant over hairless (h). Understanding this concept is crucial for predicting phenotypic ratios in offspring.
추천 영상:
가이드 코스
04:37
Variations on Dominance

Genotype and Phenotype

The genotype refers to the genetic makeup of an organism, specifically the alleles present at a given locus, while the phenotype is the observable physical or biochemical characteristics resulting from the genotype. For example, a plant with the genotype AaHhCc can exhibit a purple, hairy, cut phenotype. Analyzing the genotypes of the parental plants and their progeny helps in understanding inheritance patterns and predicting the traits of future generations.
추천 영상:
가이드 코스
07:52
Gamete Genotypes

Linkage and Recombination

Linkage refers to the tendency of genes located close to each other on the same chromosome to be inherited together, while recombination is the process that can separate linked genes during meiosis. In this scenario, the genes for leaf color and texture are separated by 16 map units (m.u.), indicating a degree of linkage. Understanding the effects of linkage and recombination is essential for predicting the expected ratios of phenotypes in the progeny from the cross described.
추천 영상:
가이드 코스
07:33
Chi Square and Linkage
관련 실천
교과서 질문

A pure-breeding tall plant producing oval fruit as described in Problem 2 is crossed to a pure-breeding short plant producing round fruit.


If the F₁ identified in part (a) are crossed to one another, what proportion of the F₂ are expected to be short and produce round fruit? What proportion are expected to be tall and produce round fruit?

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교과서 질문

In tomato plants, purple leaf color is controlled by a dominant allele A, and green leaf by a recessive allele a. At another locus, hairy leaf H is dominant to hairless leaf h. The genes for leaf color and leaf texture are separated by 16 m.u. on chromosome 5. On chromosome 4, a gene controlling leaf shape has two alleles: a dominant allele C that produces cut-leaf shape and a recessive allele c that produces potato-shaped leaves.

Fully explain the number and frequency of each phenotype class.

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교과서 질문

In Drosophila, the map positions of genes are given in map units numbering from one end of a chromosome to the other. The X chromosome of Drosophila is 66 m.u. long. The X-linked gene for body color—with two alleles, y⁺ for gray body and y for yellow body—resides at one end of the chromosome at map position 0.0. A nearby locus for eye color, with alleles w⁺ for red eye and w for white eye, is located at map position 1.5. A third X-linked gene, controlling bristle form, with f⁺ for normal bristles and f for forked bristles, is located at map position 56.7. At each locus the wild-type allele is dominant over the mutant allele.


In a cross involving these three X-linked genes, do you expect any gene pair(s) to show genetic linkage? Explain your reasoning.

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교과서 질문

A pure-breeding tall plant producing oval fruit as described in Problem 2 is crossed to a pure-breeding short plant producing round fruit.


The F₁ are crossed to short plants producing oval fruit. What are the expected proportions of progeny phenotypes?

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교과서 질문

Genes E and H are syntenic in an experimental organism with the genotype EH/eh. Assume that during each meiosis, one crossover occurs between these genes. No homologous chromosomes escape crossover, and none undergo double crossover. Are genes E and H genetically linked? Why or why not? What is the proportion of parental gametes produced by meiosis?

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교과서 질문

In Drosophila, the map positions of genes are given in map units numbering from one end of a chromosome to the other. The X chromosome of Drosophila is 66 m.u. long. The X-linked gene for body color—with two alleles, y⁺ for gray body and y for yellow body—resides at one end of the chromosome at map position 0.0. A nearby locus for eye color, with alleles w⁺ for red eye and w for white eye, is located at map position 1.5. A third X-linked gene, controlling bristle form, with f⁺ for normal bristles and f for forked bristles, is located at map position 56.7. At each locus the wild-type allele is dominant over the mutant allele.


Do you expect any of these gene pair(s) to assort independently? Explain your reasoning.

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