Mendelian Genetics and Extensions — Laws of Inheritance, Probability, and Genetic Disorders Explained | Chapter 14 of Campbell Biology

Mendelian Genetics and Extensions — Laws of Inheritance, Probability, and Genetic Disorders Explained | Chapter 14 of Campbell Biology

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Welcome to Last Minute Lecture! This post explores Mendelian genetics and its modern extensions, as presented in Chapter 14 of Campbell Biology. Discover how Gregor Mendel’s experiments laid the foundation for understanding how genes are inherited, how probability laws predict genetic outcomes, and how more complex inheritance patterns go beyond simple dominance and recessiveness. Watch the full video summary below and subscribe for clear, chapter-by-chapter genetics lessons!

Introduction: Mendel’s Legacy in Genetics

Gregor Mendel’s work with pea plants established the laws of segregation and independent assortment—principles that remain at the core of modern genetics. This chapter shows how Mendel’s discoveries explain both simple and complex inheritance in all living things, including humans.

Mendel’s Laws of Inheritance

  • Law of Segregation: Each organism carries two alleles for each gene, which segregate during gamete formation so offspring inherit one allele from each parent.
  • Law of Independent Assortment: Genes located on different chromosomes are inherited independently, producing diverse combinations of traits.

Probability and Inheritance

  • Multiplication Rule: The probability of two independent events both occurring is the product of their probabilities.
  • Addition Rule: The probability of an event occurring in multiple ways is the sum of the individual probabilities.
  • Punnett Squares: Used to predict genetic outcomes of crosses, including monohybrid (one trait) and dihybrid (two traits) crosses.

Beyond Mendelian Genetics: Extensions and Exceptions

  • Incomplete Dominance: Heterozygotes display an intermediate phenotype (e.g., pink flowers from red and white parents).
  • Codominance: Both alleles are fully expressed (e.g., AB blood type).
  • Pleiotropy: One gene influences multiple traits (e.g., sickle-cell disease).
  • Epistasis: One gene affects the expression of another (e.g., coat color in Labradors).
  • Polygenic Inheritance: Multiple genes collectively influence a single trait (e.g., skin color, height).

Human Genetics, Pedigrees, and Genetic Disorders

  • Pedigree Analysis: Diagrams showing inheritance patterns across generations help identify genetic disorders and carrier status.
  • Recessive Disorders: Only expressed when two recessive alleles are present (e.g., cystic fibrosis, Tay-Sachs disease).
  • Dominant Disorders: Expressed with just one dominant allele (e.g., Huntington’s disease).
  • Genetic Testing: Includes carrier screening, prenatal diagnostics (amniocentesis, chorionic villus sampling), and newborn screening for early detection of genetic conditions.

Key Terms and Glossary

  • Allele: Variant form of a gene.
  • Codominance: Both alleles expressed equally in a heterozygote.
  • Dihybrid Cross: Cross that tracks inheritance of two traits.
  • Epistasis: One gene alters or masks the effect of another gene.
  • Genotype: An organism’s genetic makeup.
  • Homozygous: Having two identical alleles for a gene.
  • Incomplete Dominance: Phenotype is a blend of parental traits.
  • Pleiotropy: One gene affects multiple traits.
  • Polygenic Inheritance: Trait controlled by several genes.
  • Punnett Square: Diagram used to predict inheritance outcomes.

Conclusion: Mendelian Genetics in Modern Biology

Chapter 14 of Campbell Biology demonstrates how Mendel’s principles, extended by discoveries in molecular genetics, explain both simple and complex traits. Understanding these inheritance patterns and their exceptions is crucial for fields ranging from medicine to evolutionary biology. For a detailed breakdown, watch our full video summary and keep learning with Last Minute Lecture.

If this summary clarified Mendelian genetics and modern inheritance, watch the video above and subscribe to our channel for more expert science guides and textbook breakdowns.

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