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
All textbooksSanders 3rd EditionCh. 2 - Transmission GeneticsProblem 37b
Chapter 2, Problem 37b

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.

Verified step by step guidance
1
Understand the inheritance pattern: Galactosemia is an autosomal recessive disorder, meaning that an individual must inherit two copies of the recessive allele (one from each parent) to express the disorder. Carriers have one recessive allele and one dominant allele, and they do not show symptoms of the disorder.
Analyze Amanda's family history: Amanda is healthy, but her brother Alonzo has galactosemia. Since Alonzo has the disorder, both of their parents must be carriers (heterozygous) because they passed on the recessive allele to Alonzo. Amanda, being healthy, could either be a carrier (heterozygous) or homozygous dominant. Use a Punnett square to determine the probability of Amanda being a carrier.
Set up the Punnett square for Amanda's parents: Each parent is heterozygous (Aa). The possible offspring genotypes are: AA (homozygous dominant, not a carrier), Aa (heterozygous, carrier), and aa (homozygous recessive, affected). The probabilities are 1/4 for AA, 1/2 for Aa, and 1/4 for aa. Since Amanda is healthy, she cannot be aa, so the probability of her being a carrier (Aa) is the proportion of carriers among the healthy offspring.
Analyze Brice's family history: Brice is healthy, but his sister Brianna has galactosemia. Similar to Amanda's case, both of Brice's parents must be carriers (heterozygous) because they passed on the recessive allele to Brianna. Brice, being healthy, could either be a carrier (heterozygous) or homozygous dominant. Use a Punnett square to determine the probability of Brice being a carrier.
Set up the Punnett square for Brice's parents: Each parent is heterozygous (Aa). The possible offspring genotypes are the same as Amanda's case: AA (homozygous dominant, not a carrier), Aa (heterozygous, carrier), and aa (homozygous recessive, affected). Since Brice is healthy, he cannot be aa, so the probability of him being a carrier (Aa) is the proportion of carriers among the healthy offspring.

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.

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, one inherited from each parent. In the case of galactosemia, both parents must be carriers of the recessive allele for their child to be affected. If both parents are healthy but have an affected child, they are likely carriers, which is crucial for determining the carrier status of siblings.
Recommended video:
Guided course
09:08
Autosomal Pedigrees

Carrier Probability

The probability of being a carrier for a recessive genetic disorder can be calculated using family history and Punnett squares. In this scenario, since Amanda and Brice have healthy parents but affected siblings, there is a 2/3 chance that they are carriers. This is derived from the fact that if both parents are carriers, there is a 25% chance for an affected child, leaving a 66.67% chance for the siblings to be carriers.
Recommended video:
Guided course
07:41
Probability

Punnett Square Analysis

A Punnett square is a tool used in genetics to predict the genotypes of offspring from parental alleles. By setting up a Punnett square for the potential genotypes of Amanda and Brice's parents, one can visualize the inheritance patterns and calculate the likelihood of being a carrier. This method helps clarify the genetic probabilities based on the known genotypes of the family members.
Recommended video:
Guided course
02:48
Chi Square Analysis
Related Practice
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.

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.

1097
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
Textbook Question

Sweet yellow tomatoes with a pear shape bring a high price per basket to growers. Pear shape, yellow color, and terminal flower position are recessive traits produced by alleles f, r, and t, respectively. The dominant phenotypes for each trait—full shape, red color, and axial flower position—are the product of dominant alleles F, R, and T. A farmer has two pure-breeding tomato lines. One is full, yellow, terminal and the other is pear, red, axial. Design a breeding experiment that will produce a line of tomato that is pure-breeding for pear shape, yellow color, and axial flower position.

634
views