Table of contents

1. Introduction to Genetics51m
2. Mendel's Laws of Inheritance3h 37m
3. Extensions to Mendelian Inheritance2h 41m
4. Genetic Mapping and Linkage2h 28m
5. Genetics of Bacteria and Viruses1h 21m
6. Chromosomal Variation1h 48m
7. DNA and Chromosome Structure56m
8. DNA Replication1h 10m
9. Mitosis and Meiosis1h 34m
10. Transcription1h 0m
11. Translation58m
12. Gene Regulation in Prokaryotes1h 19m
13. Gene Regulation in Eukaryotes44m
14. Genetic Control of Development44m
15. Genomes and Genomics1h 50m
16. Transposable Elements47m
17. Mutation, Repair, and Recombination1h 6m
18. Molecular Genetic Tools19m
- Genetic Cloning
  9m
- Methods for Analyzing DNA
  9m
19. Cancer Genetics29m
- Overview of Cancer
  21m
- Cancer Mutations
  7m
20. Quantitative Genetics1h 26m
21. Population Genetics50m
- Hardy Weinberg
  19m
- Allelic Frequency Changes
  31m
22. Evolutionary Genetics29m

2. Mendel's Laws of Inheritance

Pedigrees

Genetics

2. Mendel's Laws of Inheritance

Pedigrees

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1:49 minutes

Problem A.3

Textbook Question

A couple comes into your genetic counseling practice with a question about the chance a future child of theirs might have a genetic disease. Three or four men in the woman's family, including her father, had a condition that might be genetic. Although her father is still alive, she has had little contact with him for much of her life and cannot describe or name the condition. Her partner is a healthy man whose family has no history indicating the presence of a genetic condition. To provide more information about this possible genetic condition for the couple, what is the first step you recommend?

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Begin by gathering detailed information about the genetic condition in the woman's family. This includes identifying affected individuals, their relationship to the woman, and any medical records or diagnoses available for her father or other family members.

Determine the inheritance pattern of the condition. Based on the information provided, assess whether the condition might follow an autosomal dominant, autosomal recessive, X-linked, or mitochondrial inheritance pattern. This can be inferred from the number of affected males and the family structure.

Recommend genetic testing for the woman's father, as he is a living affected individual. Testing can help identify the specific genetic mutation or condition, which is crucial for understanding the risk to future offspring.

If the genetic condition is identified in the father, consider testing the woman to determine whether she is a carrier or affected by the same genetic mutation. This step is essential for assessing her risk of passing the condition to her children.

Once the genetic information is obtained, calculate the probability of the couple's future child inheriting the condition based on the inheritance pattern and the woman's carrier or affected status. Provide counseling to the couple about their reproductive options, including prenatal testing or assisted reproductive technologies if necessary.

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Key Concepts

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

Family History Assessment

Understanding the family history is crucial in genetic counseling, as it helps identify potential hereditary conditions. By gathering detailed information about the health of relatives, particularly those with known genetic disorders, counselors can assess the risk of passing on genetic diseases to future children. This step often involves constructing a pedigree to visualize inheritance patterns.

Autosomal Dominant and Recessive Inheritance

Genetic conditions can be inherited in various patterns, with autosomal dominant and recessive being the most common. In autosomal dominant inheritance, only one copy of the mutated gene from an affected parent can cause the condition, while in autosomal recessive inheritance, two copies (one from each parent) are necessary. Understanding these patterns helps predict the likelihood of a child inheriting a genetic condition.

Genetic Testing Options

Genetic testing can provide valuable information about the risk of inherited conditions. In this scenario, testing the woman for known mutations associated with her family's condition, if identified, can clarify her risk of being a carrier. Additionally, carrier screening for her partner may also be recommended to assess the combined risk for their future children.

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Albinism in humans is inherited as a simple recessive trait. For the following families, determine the genotypes of the parents and offspring. (When two alternative genotypes are possible, list both.)

Construct a pedigree of the families in (b) and (c). Assume that one of the normal children in (b) and one of the albino children in (c) become the parents of eight children. Add these children to the pedigree, predicting their phenotypes (normal or albino).

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Textbook Question

A normal male and an albino female have six children, three normal and three albino.

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A normal male and an albino female have six children, all normal.

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Two normal parents have five children: four normal and one albino.

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Textbook Question

In mice, black coat color is dominant to white coat color. In the pedigree shown here, mice with a black coat are represented by darkened symbols, and those with white coats are shown as open symbols. Using allele symbols B and b, determine the genotypes for each mouse.

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Textbook Question

Nail–patella syndrome is an autosomal disorder affecting the shape of nails on fingers and toes as well as the structure of kneecaps. The pedigree below shows the transmission of nail–patella syndrome in a family along with ABO blood type.

Explain why III-11 has nail–patella syndrome and III-12 does not. Give genotypes for these two individuals.

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Textbook Question

Does this family give evidence of genetic linkage between nail–patella syndrome and ABO blood group? Why or why not?

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Textbook Question

Is nail–patella syndrome a dominant or a recessive condition? Explain your reasoning.

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