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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1:41 minutes

Problem 22b

Textbook Question

Draw all possible conclusions concerning the mode of inheritance of the trait portrayed in the following limited pedigree.

Verified step by step guidance

Step 1: Analyze the pedigree chart to identify the affected individuals. In this chart, affected individuals are represented by shaded squares (males) or circles (females). Note that no individuals are shaded, indicating no affected individuals in this pedigree.

Step 2: Determine whether the trait could be autosomal dominant. For an autosomal dominant trait, affected individuals would appear in every generation, and at least one parent of an affected individual would also be affected. Since no individuals are shaded, this trait is unlikely to be autosomal dominant.

Step 3: Consider whether the trait could be autosomal recessive. For an autosomal recessive trait, affected individuals may appear sporadically, often skipping generations, and both parents of an affected individual must be carriers. Since no individuals are shaded, this trait is unlikely to be autosomal recessive.

Step 4: Evaluate whether the trait could be X-linked dominant. For X-linked dominant traits, affected males pass the trait to all daughters but no sons, and affected females can pass the trait to both sons and daughters. Again, no individuals are shaded, so this trait is unlikely to be X-linked dominant.

Step 5: Assess whether the trait could be X-linked recessive. For X-linked recessive traits, affected males are more common, and females are typically carriers unless both X chromosomes carry the mutation. Since no individuals are shaded, this trait is unlikely to be X-linked recessive. The absence of affected individuals suggests the trait may not be expressed in this pedigree or may require additional information to determine its mode of inheritance.

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Key Concepts

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

Pedigree Analysis

Pedigree analysis is a genetic tool used to trace the inheritance patterns of traits through generations in a family. It involves constructing a family tree that illustrates the relationships between individuals and the presence or absence of specific traits. By analyzing the pedigree, geneticists can infer whether a trait is dominant, recessive, autosomal, or sex-linked based on how it is passed down through generations.

Modes of Inheritance

Modes of inheritance refer to the patterns by which genetic traits are transmitted from parents to offspring. The primary modes include autosomal dominant, autosomal recessive, X-linked dominant, and X-linked recessive. Understanding these modes helps in predicting the likelihood of offspring inheriting certain traits based on the genotypes of the parents and the observed phenotypes in the pedigree.

Genotype vs. Phenotype

Genotype refers to the genetic makeup of an individual, while phenotype is the observable expression of that genotype, influenced by environmental factors. In pedigree analysis, distinguishing between genotype and phenotype is crucial for determining inheritance patterns. For example, a dominant phenotype may arise from either homozygous dominant or heterozygous genotypes, complicating the interpretation of the pedigree.

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Textbook Question

The accompanying pedigree shows the transmission of a phenotypic character. Using B to represent a dominant allele and b to represent a recessive allele,

Give the genotype(s) possible for each member of the family, assuming the trait is autosomal recessive.

The accompanying pedigree shows the transmission of a phenotypic character. Using B to represent a dominant allele and b to represent a recessive allele,

Give the genotype(s) possible for each member of the family, assuming the trait is autosomal dominant.

639

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Textbook Question

Draw all possible conclusions concerning the mode of inheritance of the trait portrayed in the following limited pedigree.

732

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Textbook Question

Draw all possible conclusions concerning the mode of inheritance of the trait portrayed in the following limited pedigree.

496

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Textbook Question

Draw all possible conclusions concerning the mode of inheritance of the trait portrayed in the following limited pedigree.

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Textbook Question

For decades scientists have been perplexed by different circumstances surrounding families with rare, early-onset auditory neuropathy (deafness). In some families, parents and grandparents of the proband have normal hearing, while in other families, a number of affected (deaf) family members are scattered throughout the pedigree, appearing in every generation. Assuming a genetic cause for each case, offer a reasonable explanation for the genetic origin of such deafness in the two types of families.

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Textbook Question

A 'wrongful birth' case was recently brought before a court in which a child with Smith–Lemli–Opitz syndrome was born to apparently healthy parents. This syndrome is characterized by a cluster of birth defects including cleft palate, and an array of problems with the reproductive and urinary organs. Originally considered by their physician as having a nongenetic basis, the parents decided to have another child, who was also born with Smith–Lemli–Opitz syndrome. In the role of a genetic counselor, instruct the court about what occurred, including the probability of the parents having two affected offspring, knowing that the disorder is inherited as a recessive trait.

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