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Ch. 2 - Transmission Genetics
Sanders - Genetic Analysis: An Integrated Approach 3rd Edition
Sanders3rd EditionGenetic Analysis: An Integrated ApproachISBN: 9780135564172Not the one you use?Change textbook
All textbooksSanders 3rd EditionCh. 2 - Transmission GeneticsProblem 45b
Chapter 2, Problem 45b

Domestic dogs evolved from ancestral gray wolves. Wolves have coats of short, straight hair and lack 'furnishings,' a growth pattern marked by eyebrows and a mustache found in some domestic dogs. In domestic dogs, coat variation is controlled by allelic variation in three genes. Recessive mutant alleles in the FGF5 gene result in long hair, while dogs carrying the dominant ancestral allele have short hair. Likewise, recessive mutant alleles in the KRT71 gene result in curly hair, whereas dogs with an ancestral dominant allele have straight hair. Dominant mutant alleles in the RSPO2 gene cause the presence of furnishings, while dogs homozygous for the ancestral recessive allele have no furnishings. A pure-breeding curly- and long-haired poodle with furnishings was crossed to a pure-breeding short- and straight-haired border collie lacking furnishings


If dogs of the F₁ generation are interbred, what proportions of genotypes and phenotypes are expected in the F₂?

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Step 1: Identify the genotypes of the parental generation (P generation). The poodle is pure-breeding for curly hair (KRT71 recessive, kk), long hair (FGF5 recessive, ff), and furnishings (RSPO2 dominant, FF). The border collie is pure-breeding for straight hair (KRT71 dominant, KK), short hair (FGF5 dominant, FF), and no furnishings (RSPO2 recessive, ff).
Step 2: Determine the genotypes of the F₁ generation. Since the P generation is pure-breeding, all F₁ offspring will be heterozygous for all three genes: Kk (curly/straight hair), Ff (long/short hair), and Ff (furnishings/no furnishings).
Step 3: Set up a Punnett square for the F₂ generation. Since the F₁ generation is heterozygous for all three genes, interbreeding them will result in a 3-gene dihybrid cross. Each gene will segregate independently according to Mendel's law of independent assortment. The Punnett square will have 64 cells (4x4x4) to account for all possible combinations of alleles.
Step 4: Calculate the genotypic ratios for each gene. For each gene, the expected genotypic ratio in the F₂ generation is 1:2:1 (homozygous dominant : heterozygous : homozygous recessive). Combine these ratios for the three genes to determine the overall genotypic proportions.
Step 5: Determine the phenotypic ratios. Use the dominance relationships for each gene to predict the phenotypes. For example, dominant alleles for KRT71 (straight hair), FGF5 (short hair), and RSPO2 (furnishings) will determine the phenotypes. Combine the phenotypic effects of all three genes to calculate the proportions of each phenotype in the F₂ generation.

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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, genotype versus phenotype, and how these factors influence the inheritance patterns of traits. In this context, the inheritance of coat characteristics in dogs follows Mendelian principles, where specific alleles determine the observable traits.
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Allelic Variation

Allelic variation refers to the different forms of a gene (alleles) that can exist at a specific locus on a chromosome. In the case of domestic dogs, variations in the FGF5, KRT71, and RSPO2 genes lead to different coat types and features. Understanding how these alleles interact—whether they are dominant or recessive—is crucial for predicting the phenotypic outcomes in the offspring of the cross described in the question.
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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 allows for the visualization of how alleles from each parent combine in the F1 generation and how they segregate in the F2 generation. By setting up a Punnett square for the cross between the curly- and long-haired poodle and the short- and straight-haired border collie, one can determine the expected proportions of genotypes and phenotypes in the resulting offspring.
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Related Practice
Textbook Question

Situs inversus is a congenital condition in which the major visceral organs are reversed from their normal positions. Investigations into the genetics of this abnormality revealed that individuals with at least one dominant allele (SI) of an autosomal gene are normal but, surprisingly, of individuals that are homozygous for a recessive allele (si), 1/2 are situs inversus and 1/2 are normal.


What genotypes and phenotypes are expected in progeny from a cross of two si si individuals?

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Textbook Question

Situs inversus is a congenital condition in which the major visceral organs are reversed from their normal positions. Investigations into the genetics of this abnormality revealed that individuals with at least one dominant allele (SI) of an autosomal gene are normal but, surprisingly, of individuals that are homozygous for a recessive allele (si), 1/2 are situs inversus and 1/2 are normal.


What genotypes and phenotypes are expected in progeny from a cross of two SI si individuals?

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Textbook Question

Domestic dogs evolved from ancestral gray wolves. Wolves have coats of short, straight hair and lack 'furnishings,' a growth pattern marked by eyebrows and a mustache found in some domestic dogs. In domestic dogs, coat variation is controlled by allelic variation in three genes. Recessive mutant alleles in the FGF5 gene result in long hair, while dogs carrying the dominant ancestral allele have short hair. Likewise, recessive mutant alleles in the KRT71 gene result in curly hair, whereas dogs with an ancestral dominant allele have straight hair. Dominant mutant alleles in the RSPO2 gene cause the presence of furnishings, while dogs homozygous for the ancestral recessive allele have no furnishings. A pure-breeding curly- and long-haired poodle with furnishings was crossed to a pure-breeding short- and straight-haired border collie lacking furnishings


What are the genotypes and phenotypes of the puppies?

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Textbook Question

Alleles of the IGF-1 gene in dogs, encoding insulin-like growth factor, largely determine whether a domestic dog will be large or small. Dogs with an ancestral dominant allele are large, whereas dogs homozygous for the mutant recessive allele are small. Chondrodysplasia, a short-legged phenotype (as in dachshunds and basset hounds), is caused by a dominant gain-of-function allele of the FGF4 gene. The MSTN gene encodes myostatin, a regulator of muscle development. Dogs with a dominant ancestral allele of the MTSN gene have normal muscle development, while dogs homozygous for recessive mutants in the MTSN gene are 'double muscled' and have trouble running quickly. However, dogs heterozygous for the mutant allele run faster than either of the homozygotes.

You breed a pure-breeding small basset hound of normal musculature with a pure-breeding 'bully' whippet, a double-muscled large dog with normal legs.

What are the genotypes and phenotypes of the F₁ puppies?

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Textbook Question

Alleles of the IGF-1 gene in dogs, encoding insulin-like growth factor, largely determine whether a domestic dog will be large or small. Dogs with an ancestral dominant allele are large, whereas dogs homozygous for the mutant recessive allele are small. Chondrodysplasia, a short-legged phenotype (as in dachshunds and basset hounds), is caused by a dominant gain-of-function allele of the FGF4 gene. The MSTN gene encodes myostatin, a regulator of muscle development. Dogs with a dominant ancestral allele of the MTSN gene have normal muscle development, while dogs homozygous for recessive mutants in the MTSN gene are 'double muscled' and have trouble running quickly. However, dogs heterozygous for the mutant allele run faster than either of the homozygotes.

You breed a pure-breeding small basset hound of normal musculature with a pure-breeding 'bully' whippet, a double-muscled large dog with normal legs.

If the F₁ of this cross is interbred, what proportion of the F₂ are expected to be fast runners and what proportion normal-speed runners?

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Textbook Question

The accompanying pedigree shows a family in which one child (II-1) has an autosomal recessive condition. On the basis of this fact alone, provide the following information.

Using A for the dominant allele and a for the recessive allele, give the genotypes for I-1, I-2, and II-1.

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