Skip to main content
Pearson+ LogoPearson+ Logo
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
Chapter 2, Problem 37a

Galactosemia is an autosomal recessive disorder caused by the inability to metabolize galactose, a component of the lactose found in mammalian milk. Galactosemia can be partially managed by eliminating dietary intake of lactose and galactose. Amanda is healthy, as are her parents, but her brother Alonzo has galactosemia. Brice has a similar family history. He and his parents are healthy, but his sister Brianna has galactosemia. Amanda and Brice are planning a family and seek genetic counseling. Based on the information provided, complete the following activities and answer the questions.
Draw a pedigree that includes Amanda, Brice, and their siblings and parents. Identify the genotype of each person, using G and g to represent the dominant and recessive alleles, respectively.

Verified step by step guidance
1
Step 1: Understand the inheritance pattern of galactosemia. Since it is an autosomal recessive disorder, individuals with the genotype 'gg' will have the disorder, while those with 'GG' or 'Gg' will be healthy. Carriers (heterozygous 'Gg') do not show symptoms but can pass the recessive allele to their offspring.
Step 2: Analyze the family history provided. Amanda and Brice are healthy, but each has a sibling with galactosemia. This indicates that Amanda and Brice are likely carriers (Gg), as their parents must also be carriers (Gg) to produce offspring with the 'gg' genotype.
Step 3: Draw the pedigree. Start with Amanda and Brice's grandparents (assume unknown genotypes unless specified). Then include their parents, siblings, and themselves. Use standard pedigree symbols: squares for males, circles for females, shading for affected individuals, and unshaded for unaffected individuals. Connect family members with lines to represent relationships.
Step 4: Assign genotypes to each individual in the pedigree. For Amanda and Brice's siblings with galactosemia, assign 'gg'. For Amanda, Brice, and their parents, assign 'Gg' (carriers). If grandparents are not specified, leave their genotypes unknown or infer based on the parents' genotypes.
Step 5: Use the completed pedigree to predict the likelihood of Amanda and Brice passing galactosemia to their children. Since both are carriers (Gg), use a Punnett square to calculate the probabilities of their offspring being 'GG', 'Gg', or 'gg'.

Verified video answer for a similar problem:

This video solution was recommended by our tutors as helpful for the problem above.
Video duration:
3m
Was this helpful?

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 disorder is expressed only when an individual has two copies of the recessive allele. In the case of galactosemia, both parents must carry at least one recessive allele (g) for their child to be affected. This means that healthy parents can still be carriers (genotype Gg) and pass the recessive allele to their offspring.
Recommended video:
Guided course
09:08
Autosomal Pedigrees

Pedigree Analysis

A pedigree is a diagram that represents the genetic relationships within a family over generations. It is used to track the inheritance of traits, such as galactosemia, and can help identify carriers and affected individuals. Symbols in a pedigree denote males, females, affected individuals, and carriers, allowing for visual representation of genetic information.
Recommended video:
Guided course
01:59
Pedigree Flowchart

Genotype Notation

Genotype notation uses letters to represent the alleles an individual possesses for a particular gene. In this context, 'G' represents the dominant allele (normal function) and 'g' represents the recessive allele (defective function). Understanding genotype notation is crucial for determining the genetic makeup of individuals in the pedigree and predicting the likelihood of offspring inheriting galactosemia.
Recommended video:
Guided course
07:52
Gamete Genotypes
Related Practice
Textbook Question

A man and a woman are each heterozygous carriers of an autosomal recessive mutation of a disorder that is fatal in infancy. They both want to have multiple children, but they are concerned about the risk of the disorder appearing in one or more of their children. In separate calculations, determine the probabilities of the couple having five children with 0, 1, 2, 3, 4, and all 5 children being affected by the disorder.

601
views
Textbook Question

For a single dice roll, there is a 1/6 chance that any particular number will appear. For a pair of dice, each specific combination of numbers has a probability of 1/36 occurring. Most total values of two dice can occur more than one way. As a test of random probability theory, a student decides to roll a pair of six-sided dice 300 times and tabulate the results. She tabulates the number of times each different total value of the two dice occurs. Her results are the following:

Total Value of Two Dice      Number of Times Rolled
               2                                          7
               3                                         11
               4                                         23
               5                                         36
               6                                         42
               7                                         53
               8                                         40
               9                                         38
              10                                        30
              11                                        12
              12                                         8
           TOTAL                                   300

The student tells you that her results fail to prove that random chance is the explanation for the outcome of this experiment. Is she correct or incorrect? Support your answer.

515
views
Textbook Question

You have four guinea pigs for a genetic study. One male and one female are from a strain that is pure-breeding for short brown fur. A second male and female are from a strain that is pure-breeding for long white fur. You are asked to perform two different experiments to test the proposal that short fur is dominant to long fur and that brown is dominant to white. You may use any of the four original pure-breeding guinea pigs or any of their offspring in experimental matings. Design two different experiments (crossing different animals and using different combinations of phenotypes) to test the dominance relationships of alleles for fur length and color, and make predictions for each cross based on the proposed relationships. Anticipate that the litter size will be 12 for each mating and that female guinea pigs can produce three litters in their lifetime.

431
views
Textbook Question

Galactosemia is an autosomal recessive disorder caused by the inability to metabolize galactose, a component of the lactose found in mammalian milk. Galactosemia can be partially managed by eliminating dietary intake of lactose and galactose. Amanda is healthy, as are her parents, but her brother Alonzo has galactosemia. Brice has a similar family history. He and his parents are healthy, but his sister Brianna has galactosemia. Amanda and Brice are planning a family and seek genetic counseling. Based on the information provided, complete the following activities and answer the questions.


What is the probability that Amanda is a carrier of the allele for galactosemia? What is the probability that Brice is a carrier? Explain your reasoning for each answer.

433
views
Textbook Question

Galactosemia is an autosomal recessive disorder caused by the inability to metabolize galactose, a component of the lactose found in mammalian milk. Galactosemia can be partially managed by eliminating dietary intake of lactose and galactose. Amanda is healthy, as are her parents, but her brother Alonzo has galactosemia. Brice has a similar family history. He and his parents are healthy, but his sister Brianna has galactosemia. Amanda and Brice are planning a family and seek genetic counseling. Based on the information provided, complete the following activities and answer the questions.


What is the probability that the first child of Amanda and Brice will have galactosemia? Show your work.

688
views
Textbook Question

Galactosemia is an autosomal recessive disorder caused by the inability to metabolize galactose, a component of the lactose found in mammalian milk. Galactosemia can be partially managed by eliminating dietary intake of lactose and galactose. Amanda is healthy, as are her parents, but her brother Alonzo has galactosemia. Brice has a similar family history. He and his parents are healthy, but his sister Brianna has galactosemia. Amanda and Brice are planning a family and seek genetic counseling. Based on the information provided, complete the following activities and answer the questions.


If the first child has galactosemia, what is the probability that the second child will have galactosemia? Explain the reasoning for your answer.

446
views