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Ch. 14 - Mendel and the Gene
Freeman - Biological Science 8th Edition
Freeman8th EditionBiological ScienceISBN: 9780138276263Not the one you use?Change textbook
All textbooksFreeman 8th EditionCh. 14 - Mendel and the GeneProblem 6
Chapter 14, Problem 6

In peas, purple flowers are dominant to white. If a purple-flowered, heterozygous plant were crossed with a white-flowered plant, what is the expected ratio of genotypes and phenotypes among the F1 offspring? If two of the purple-flowered F1 offspring were randomly selected and crossed, what is the expected ratio of genotypes and phenotypes among the F2 offspring?

Verified step by step guidance
1
Identify the genotypes of the parent plants. The purple-flowered parent is heterozygous (Pp) and the white-flowered parent is homozygous recessive (pp).
Set up a Punnett square for the F1 generation cross between Pp and pp. The possible gametes from the purple-flowered parent are P and p, and from the white-flowered parent are p and p.
Fill in the Punnett square to find the genotypes of the F1 offspring. The resulting genotypes are Pp and pp. Since purple (P) is dominant over white (p), the phenotypic ratio is 1 purple : 1 white.
For the F2 generation, cross two purple-flowered F1 offspring (Pp x Pp). Set up a Punnett square with gametes P and p from each parent.
Fill in the Punnett square for the F2 generation. The genotypes are PP, Pp, Pp, and pp. The phenotypic ratio is 3 purple : 1 white, and the genotypic ratio is 1 PP : 2 Pp : 1 pp.

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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. In this case, the purple flower trait is dominant over the white flower trait in peas.
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Punnett Square

A Punnett square is a diagram used to predict the genotypes and phenotypes of offspring from a genetic cross. It organizes the possible combinations of alleles from the parents, allowing for easy visualization of the expected ratios. For the cross between a heterozygous purple-flowered plant and a white-flowered plant, the Punnett square helps determine the expected ratios of the F1 generation.
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Genotype and Phenotype Ratios

Genotype refers to the genetic makeup of an organism, while phenotype refers to the observable traits. In the context of the F1 and F2 generations, the expected genotype and phenotype ratios can be calculated based on the alleles inherited. For example, the F1 generation from the initial cross will show a specific ratio of purple to white flowers, while the F2 generation will exhibit a different ratio due to the combination of alleles from the F1 offspring.
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Related Practice
Textbook Question

The alleles found in haploid organisms cannot be dominant or recessive. Why?

a. Dominance and recessiveness describe which of two possible phenotypes are exhibited when two different alleles occur in the same individual.

b. Because only one allele is present, alleles in haploid organisms are always dominant.

c. Alleles in haploid individuals are transmitted like mitochondrial DNA or chloroplast DNA.

d. Most haploid individuals are bacteria, and bacterial genetics is completely different from eukaryotic genetics.

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Textbook Question

Two black female mice are crossed with a brown male. In several litters, female I produced 9 black offspring and 7 brown; female II produced 57 black offspring. What deductions can you make about the inheritance of black and brown coat color in mice? What are the genotypes of the parents?

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Textbook Question

A plant with orange, spotted flowers was grown in the greenhouse from a seed collected in the wild. The plant was self-pollinated and gave rise to the following progeny: 88 orange with spots, 34 yellow with spots, 32 orange with no spots, and 8 yellow with no spots. What can you conclude about the dominance relationships of the alleles responsible for the spotted and unspotted phenotypes? What can you conclude about the genotype of the original plant that had orange, spotted flowers?

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Textbook Question

In flies, small wings are recessive to normal wings. If a cross between two flies produces 8 small-wing offspring and 28 normal-wing offspring, what are the most likely genotypes of the parents? (Use S to represent the normal-wing allele and s to represent the short-wing allele.)

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Textbook Question

In garden peas, yellow seeds (Y) are dominant to green seeds (y), and inflated pods (I) are dominant to constricted pods (i). Suppose you have crossed YYII parents with yyii parents. Draw the F1 Punnett square and predict the expected F1 phenotype(s).

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Textbook Question

In garden peas, yellow seeds (Y) are dominant to green seeds (y), and inflated pods (I) are dominant to constricted pods (i). Suppose you have crossed YYII parents with yyii parents. List the genotype(s) of gametes produced by F1 individuals.

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