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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 46b
Chapter 2, Problem 46b

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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1
Step 1: Identify the genotypes of the parental generation (P generation). The small basset hound is homozygous recessive for the IGF-1 gene (small size), homozygous dominant for the FGF4 gene (short legs), and homozygous dominant for the MSTN gene (normal musculature). The bully whippet is homozygous dominant for the IGF-1 gene (large size), homozygous recessive for the FGF4 gene (normal legs), and homozygous recessive for the MSTN gene (double-muscled).
Step 2: Determine the genotypes of the F₁ generation. Since the P generation consists of pure-breeding individuals, the F₁ offspring will be heterozygous for all three genes: heterozygous for IGF-1 (large size), heterozygous for FGF4 (normal legs), and heterozygous for MSTN (fast runners, due to heterozygous advantage).
Step 3: Set up a Punnett square for the F₂ generation. When the F₁ individuals are interbred, each gene will segregate independently according to Mendel's laws. For each gene, the genotypic ratio in the F₂ generation will be 1:2:1 (homozygous dominant : heterozygous : homozygous recessive).
Step 4: Identify the phenotypes associated with each genotype. For the MSTN gene, homozygous dominant (normal musculature) and homozygous recessive (double-muscled) result in normal-speed runners, while heterozygous individuals are fast runners. Use the 1:2:1 ratio to calculate the proportion of fast runners (heterozygous) and normal-speed runners (homozygous dominant + homozygous recessive).
Step 5: Combine the phenotypic ratios for the MSTN gene with the other genes (IGF-1 and FGF4) if needed, but focus on the MSTN gene for the specific question about fast and normal-speed runners. The proportion of fast runners will be 2/4 (heterozygous), and the proportion of normal-speed runners will be 2/4 (homozygous dominant + homozygous recessive).

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Key Concepts

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

Alleles and Inheritance

Alleles are different forms of a gene that can exist at a specific locus on a chromosome. Inheritance patterns, such as dominant and recessive traits, determine how these alleles are expressed in offspring. For example, a dominant allele can mask the presence of a recessive allele, influencing the phenotype of the organism. Understanding these principles is crucial for predicting the traits of the F₂ generation in genetic crosses.
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New Alleles and Migration

Phenotypic Ratios

Phenotypic ratios describe the expected distribution of observable traits in the offspring resulting from a genetic cross. By applying Mendelian genetics, one can calculate the proportions of different phenotypes in the F₂ generation based on the genotypes of the F₁ generation. This concept is essential for determining how many offspring will exhibit traits such as speed in the context of the given dog breeds.
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Mutations and Phenotypes

Gene Interactions

Gene interactions occur when the effects of one gene are influenced by one or more other genes. In this scenario, the interaction between the MSTN gene and the alleles from the IGF-1 gene affects muscle development and running speed in dogs. Understanding these interactions is vital for predicting the performance of the F₂ generation, as the presence of dominant or recessive alleles can lead to varying phenotypic outcomes.
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Related Practice
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?

508
views
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


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

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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?

656
views
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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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 the same alleles, give the possible genotypes for II-2, II-3, and II-4.

775
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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.

What are the probabilities for each of the possible genotypes for II-2, II-3, and II-4?

515
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