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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 47a
Chapter 2, Problem 47a

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.
Pedigree chart showing a family with one child (II-1) affected by an autosomal recessive condition.
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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1
Step 1: Understand the inheritance pattern. The problem states that the condition is autosomal recessive, meaning that an individual must inherit two copies of the recessive allele (a) to express the condition. Individuals with one dominant allele (A) and one recessive allele (a) are carriers but do not express the condition.
Step 2: Analyze the pedigree. II-1 is affected by the autosomal recessive condition, so their genotype must be homozygous recessive (aa). This is because they inherited one recessive allele from each parent.
Step 3: Determine the genotypes of I-1 and I-2 (the parents of II-1). Since II-1 is affected, both parents must have at least one recessive allele (a) to pass it on. Therefore, I-1 and I-2 must be carriers, meaning their genotypes are heterozygous (Aa).
Step 4: Confirm the reasoning. For II-1 to inherit the condition, both parents (I-1 and I-2) must contribute a recessive allele (a). This aligns with the autosomal recessive inheritance pattern.
Step 5: Summarize the genotypes. Based on the analysis, the genotypes are: I-1 = Aa, I-2 = Aa, and II-1 = aa.

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Key Concepts

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

Autosomal Recessive Inheritance

Autosomal recessive inheritance occurs when a trait or condition is expressed only when an individual has two copies of the recessive allele (aa). If an individual has one dominant allele (A), they will not express the condition and are considered a carrier (Aa). This pattern of inheritance is crucial for understanding how traits are passed through generations, especially in pedigree analysis.
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Genotype vs. Phenotype

The genotype refers to the genetic makeup of an individual, specifically the alleles they carry (e.g., AA, Aa, or aa), while the phenotype is the observable expression of that genotype (e.g., having a certain condition or trait). In the context of the question, determining the genotypes of the individuals in the pedigree is essential to understand the inheritance pattern of the autosomal recessive condition.
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Pedigree Analysis

Pedigree analysis is a method used to trace the inheritance of traits through generations in a family. It involves constructing a diagram that represents family relationships and the presence or absence of specific traits. By analyzing the pedigree, one can infer the genotypes of individuals based on the phenotypes of affected and unaffected family members, which is critical for solving the given question.
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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


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?

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

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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?

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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 is the probability that all three of the children in generation II who have the dominant phenotype are Aa?

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