Skip to main content
Pearson+ LogoPearson+ Logo
Ch. 4 - Extensions of Mendelian Genetics
Klug - Concepts of Genetics 12th Edition
Klug12th EditionConcepts of Genetics ISBN: 9780135564776Not the one you use?Change textbook
All textbooksKlug 12th EditionCh. 4 - Extensions of Mendelian GeneticsProblem 14a
Chapter 4, Problem 14a

Horses can be cremello (a light cream color), chestnut (a brownish color), or palomino (a golden color with white in the horse's tail and mane). Of these phenotypes, only palominos never breed true.
Breeding outcomes showing ratios of cremello, palomino, and chestnut horse phenotypes from different parental crosses.
From the results given above, determine the mode of inheritance by assigning gene symbols and indicating which genotypes yield which phenotypes.

Verified step by step guidance
1
Step 1: Define gene symbols for the alleles involved. Since the problem involves coat color with three phenotypes (cremello, palomino, chestnut), assign a gene symbol such as 'C' for the cream allele and 'c' for the non-cream allele. The cream allele is known to be incompletely dominant, so heterozygotes show the palomino phenotype.
Step 2: Assign genotypes to each phenotype based on the inheritance pattern. For example, 'CC' could represent cremello (homozygous cream), 'Cc' palomino (heterozygous cream), and 'cc' chestnut (no cream allele). This fits the description that palominos never breed true, as they are heterozygotes.
Step 3: Use the given breeding outcomes to confirm the genotypes. For instance, crossing cremello (CC) with palomino (Cc) yields 1/2 cremello (CC) and 1/2 palomino (Cc), matching the data. Similarly, chestnut (cc) crossed with palomino (Cc) yields 1/2 chestnut (cc) and 1/2 palomino (Cc).
Step 4: Analyze the palomino × palomino cross, which produces 1/2 palomino (Cc), 1/4 cremello (CC), and 1/4 chestnut (cc). This confirms the incomplete dominance pattern where heterozygotes show the intermediate phenotype (palomino).
Step 5: Summarize the mode of inheritance as incomplete dominance with the cream allele 'C' incompletely dominant over the non-cream allele 'c', resulting in three phenotypes: CC = cremello, Cc = palomino, and cc = chestnut.

Verified video answer for a similar problem:

This video solution was recommended by our tutors as helpful for the problem above.
Video duration:
1m
Was this helpful?

Key Concepts

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

Incomplete Dominance

Incomplete dominance occurs when heterozygous individuals display a phenotype that is intermediate between the two homozygous phenotypes. In this case, palomino horses represent the heterozygous phenotype, showing a blend of chestnut and cremello traits rather than one being completely dominant.
Recommended video:
Guided course
04:37
Variations on Dominance

Genotype-Phenotype Relationship

Understanding how specific genotypes correspond to observable phenotypes is crucial. Here, assigning gene symbols (e.g., C for cream allele and c for chestnut allele) helps explain the phenotypes: cremello (CC), chestnut (cc), and palomino (Cc), with palomino being heterozygous and showing an intermediate color.
Recommended video:
Guided course
07:52
Gamete Genotypes

Breeding Ratios and Predicting Offspring

Analyzing breeding outcomes and offspring ratios allows determination of inheritance patterns. The given crosses and resulting phenotypic ratios (e.g., 1/2 cremello and 1/2 palomino from cremello × palomino) support the incomplete dominance model and help predict genotypes and phenotypes of future generations.
Recommended video:
Guided course
08:06
Mendel's Experiments
Related Practice
Textbook Question

In rabbits, a series of multiple alleles controls coat color in the following way: C is dominant to all other alleles and causes full color. The chinchilla phenotype is due to the cch allele, which is dominant to all alleles other than C. The ch allele, dominant only to (albino), results in the Himalayan coat color. Thus, the order of dominance is C > cch > ch > ca. For each of the following three cases, the phenotypes of the P1 generations of two crosses are shown, as well as the phenotype of one member of the F1 generation.

For each case, determine the genotypes of the P1 generation and the F1 offspring, and predict the results of making each indicated cross between F1 individuals.

5024
views
Textbook Question

Three gene pairs located on separate autosomes determine flower color and shape as well as plant height. The first pair exhibits incomplete dominance, where the color can be red, pink (the heterozygote), or white. The second pair leads to personate (dominant) or peloric (recessive) flower shape, while the third gene pair produces either the dominant tall trait or the recessive dwarf trait. Homozygous plants that are red, personate, and tall are crossed to those that are white, peloric, and dwarf. Determine the F₁ genotype(s) and phenotype(s). If the F₁ plants are interbred, what proportion of the offspring will exhibit the same phenotype as the F₁ plants?

827
views
Textbook Question

Flower color may be red, white, or pink, and flower shape may be personate or peloric. For the following crosses, determine the P₁ and F₁ genotypes:

549
views
Textbook Question

Horses can be cremello (a light cream color), chestnut (a brownish color), or palomino (a golden color with white in the horse's tail and mane). Of these phenotypes, only palominos never breed true.

Predict the F1 and F2 results of many initial matings between cremello and chestnut horses.

546
views
Textbook Question

With reference to the eye color phenotypes produced by the recessive, autosomal, unlinked brown and scarlet loci in Drosophila, predict the F₁ and F₂ results of the following P₁ crosses. (Recall that when both the brown and scarlet alleles are homozygous, no pigment is produced, and the eyes are white.)

Wild type x White

562
views
Textbook Question

With reference to the eye color phenotypes produced by the recessive, autosomal, unlinked brown and scarlet loci in Drosophila, predict the F₁ and F₂ results of the following P₁ crosses. (Recall that when both the brown and scarlet alleles are homozygous, no pigment is produced, and the eyes are white.)

Wild type x Scarlet

649
views