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Ch. 2 - Transmission Genetics
All textbooksSanders 3rd EditionCh. 2 - Transmission GeneticsProblem 5
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Chapter 2, Problem 5

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 leaf.

The cross of a purple, hairy, cut plant heterozygous at each gene to a green, hairless, potato plant produces the following progeny:

        Phenotype             Frequency %   _
  Purple, hairy, cut                21
  Purple, hairy, potato           21
  Green, hairless, cut            21
  Green, hairless, potato       21
  Purple, hairless, cut            4
  Purple, hairless, potato.      4
  Green, hairy, cut                  4
  Green, hairy, potato.            4  _
                                             100
Give the genotypes of parental and progeny plants in this experiment.

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1
Identify the genotypes of the parental plants. The purple, hairy, cut plant is heterozygous at each gene, so its genotype is AaHhCc. The green, hairless, potato plant is homozygous recessive at each gene, so its genotype is aahhcc.
Determine the possible gametes produced by the heterozygous parent (AaHhCc). Since the genes for leaf color and leaf texture are linked and separated by 16 m.u., consider the recombination frequency to determine the gametes: AH, Ah, aH, ah.
List the possible genotypes of the progeny based on the combination of gametes from both parents. The progeny genotypes will be combinations of the gametes from AaHhCc and aahhcc.
Match the phenotypes of the progeny with their genotypes. Use the dominant and recessive allele information to determine the phenotype for each genotype.
Analyze the frequency of each phenotype to confirm the genotypes. The higher frequency phenotypes (21%) are likely non-recombinant, while the lower frequency phenotypes (4%) are likely recombinant.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Mendelian Genetics

Mendelian genetics is the study of how traits are inherited through generations based on the principles established by Gregor Mendel. It involves understanding dominant and recessive alleles, where dominant alleles mask the expression of recessive ones. This concept is crucial for predicting the genotypes and phenotypes of offspring based on parental genotypes, as seen in the cross of the tomato plants.
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Descriptive Genetics

Gene Linkage and Recombination

Gene linkage refers to the tendency of genes located close to each other on a chromosome to be inherited together during meiosis. The distance between genes, measured in map units (m.u.), indicates the likelihood of recombination occurring between them. In this question, the genes for leaf color and texture are separated by 16 m.u., which affects the expected ratios of phenotypes in the progeny.
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Chi Square and Linkage

Phenotypic Ratios

Phenotypic ratios represent the relative frequencies of different phenotypes observed in the offspring of a genetic cross. These ratios can be predicted based on the genotypes of the parents and the inheritance patterns of the alleles involved. In the given cross, the observed phenotypic frequencies provide insights into the underlying genotypes of both the parental plants and their progeny.
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Textbook Question
In a type of parakeet known as a 'budgie,' feather color is controlled by two genes. A yellow pigment is synthesized under the control of a dominant allele Y. Budgies that are homozygous for the recessive y allele do not synthesize yellow pigment. At an independently assorting gene, the dominant allele B directs synthesis of a blue pigment. Recessive homozygotes with the bb genotype do not produce blue pigment. Budgies that produce both yellow and blue pigments have green feathers; those that produce only yellow pigment or only blue pigment have yellow or blue feathers, respectively; and budgies that produce neither pigment are white (albino). A cross is made between a pure-breeding green budgie and a pure-breeding albino budgie. What are the genotypes of the parent birds?
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Textbook Question
In a type of parakeet known as a 'budgie,' feather color is controlled by two genes. A yellow pigment is synthesized under the control of a dominant allele Y. Budgies that are homozygous for the recessive y allele do not synthesize yellow pigment. At an independently assorting gene, the dominant allele B directs synthesis of a blue pigment. Recessive homozygotes with the bb genotype do not produce blue pigment. Budgies that produce both yellow and blue pigments have green feathers; those that produce only yellow pigment or only blue pigment have yellow or blue feathers, respectively; and budgies that produce neither pigment are white (albino). If F₁ males and females are mated, what phenotypes are expected in the F₂, and in what proportions?
381
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Textbook Question
In a type of parakeet known as a 'budgie,' feather color is controlled by two genes. A yellow pigment is synthesized under the control of a dominant allele Y. Budgies that are homozygous for the recessive y allele do not synthesize yellow pigment. At an independently assorting gene, the dominant allele B directs synthesis of a blue pigment. Recessive homozygotes with the bb genotype do not produce blue pigment. Budgies that produce both yellow and blue pigments have green feathers; those that produce only yellow pigment or only blue pigment have yellow or blue feathers, respectively; and budgies that produce neither pigment are white (albino). The cross of a green budgie and a yellow budgie produces offspring that are 12 green, 4 blue, 13 yellow, and 3 albino. What are the genotypes of the parents?
247
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Textbook Question

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 leaf.

Fully explain the number and frequency of each phenotype class.

310
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Textbook Question
In a type of parakeet known as a 'budgie,' feather color is controlled by two genes. A yellow pigment is synthesized under the control of a dominant allele Y. Budgies that are homozygous for the recessive y allele do not synthesize yellow pigment. At an independently assorting gene, the dominant allele B directs synthesis of a blue pigment. Recessive homozygotes with the bb genotype do not produce blue pigment. Budgies that produce both yellow and blue pigments have green feathers; those that produce only yellow pigment or only blue pigment have yellow or blue feathers, respectively; and budgies that produce neither pigment are white (albino). What are the genotype(s) and phenotype(s) of the F₁ progeny of the cross described in part (b)?
198
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Textbook Question

Consider the cross AaBbCC×AABbCc.

How many different gamete genotypes can each organism produce?

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