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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: 9780135564172Not the one you use?Change textbook
Chapter 5, Problem 3a

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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1
Determine the genotypes of the pure-breeding parents. A pure-breeding tall plant producing oval fruit can be represented as TTFF (where T = tall, t = short, F = oval, f = round). A pure-breeding short plant producing round fruit can be represented as ttff.
Perform the first cross between the pure-breeding parents (TTFF x ttff). Use a Punnett square to determine the genotypes of the F₁ generation. All F₁ offspring will be heterozygous for both traits (TtFf), as they inherit one allele from each parent.
Cross the F₁ plants (TtFf) with short plants producing oval fruit (ttFf). This is a test cross, and you will need to consider the independent assortment of the two traits. Set up a Punnett square for the cross TtFf x ttFf, considering all possible combinations of alleles.
Determine the phenotypes of the progeny based on the genotypes from the Punnett square. Recall that T (tall) is dominant over t (short), and F (oval) is dominant over f (round). For each genotype, assign the corresponding phenotype.
Calculate the expected proportions of each phenotype by counting the occurrences of each phenotype in the Punnett square and dividing by the total number of progeny. This will give you the expected phenotypic ratios.

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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 traits mask the expression of recessive ones. This framework helps predict the phenotypic ratios of offspring from specific parental crosses.
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Descriptive Genetics

Phenotype and Genotype

The phenotype refers to the observable characteristics of an organism, such as height or fruit shape, while the genotype is the genetic makeup that determines these traits. In this context, understanding the relationship between genotype and phenotype is crucial for predicting the traits of the progeny resulting from the crosses described in the question.
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Gamete Genotypes

Punnett Square

A Punnett square is a diagram used to predict the genetic outcomes of a cross between two organisms. It allows for the visualization of how alleles from each parent combine to form the genotypes of the offspring. By filling out a Punnett square based on the parental genotypes, one can easily determine the expected proportions of different phenotypes in the progeny.
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Related Practice
Textbook Question

Give the information requested.


Progeny of the cross Rt/rT×rt/rt

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Textbook Question

In a diploid species of plant, the genes for plant height and fruit shape are syntenic and separated by 18 m.u. Allele D produces tall plants and is dominant to d for short plants, and allele R produces round fruit and is dominant to r for oval fruit.


A plant with the genotype DR/dr produces gametes. Identify gamete genotypes, label parental and recombinant gametes, and give the frequency of each gamete genotype.

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Textbook Question

In a diploid species of plant, the genes for plant height and fruit shape are syntenic and separated by 18 m.u. Allele D produces tall plants and is dominant to d for short plants, and allele R produces round fruit and is dominant to r for oval fruit.


Give the same information for a plant with the genotype Dr/dR.

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Textbook Question

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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Textbook Question

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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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 leaves.

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

 

Give the genotypes of parental and progeny plants in this experiment.

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