Patterns of Inheritance - Chapter 7

• Key Terms

  • Genotype: The genetic makeup of an organism; the combination of alleles.

  • Phenotype: The observable physical or biochemical characteristics of an organism; expressed traits resulting from the genotype.

• Mendel's Contributions

  • Gregor Mendel: Conducted experiments with pea plants in the mid-1800s, laying the foundation for genetics.

  • Mendel’s Laws:

  • Law of Segregation: Two alleles for a trait segregate during gamete formation (meiosis) and reunite during fertilization.

  • Law of Independent Assortment: Different traits assort independently of each other during gamete formation.

• Punnett Squares

  • A grid used to predict the genotypes and phenotypes of offspring from genetic crosses.

  • Example: A cross between two heterozygous black-coated dogs (Bb) yields:

  • Genotypic Ratio: 1 BB : 2 Bb : 1 bb

  • Phenotypic Ratio: 3 Black : 1 Brown

• Types of Genetic Traits

  • Mendelian Traits: Traits governed by a single gene (e.g., fur color) and unaffected by environmental factors.

  • Complex Traits: Traits influenced by multiple genes and environmental factors (e.g., height, skin color).

  • Pleiotropy: A single gene affects multiple traits (e.g., a single gene influencing both coat color and head shape in dogs).

  • Polygenic Traits: Traits controlled by multiple genes (e.g., human skin color).

  • Codominance: Both alleles are expressed equally in the phenotype (e.g., AB blood type).

  • Incomplete Dominance: The phenotype is a blend of the two traits (e.g., red and white flowers produce pink offspring).

• Epistasis: One gene's allele affects the expression of another gene (e.g., Labrador retriever coat color).

• Environmental Influence

  • External and internal environments can affect genetic expression leading to variations in phenotype such as temperature sensitivity in Siamese cats' fur coloration.

• Genetic Disorders

  • Cystic Fibrosis: A Mendelian disorder with genotypes LL (normal) vs. ll (affected). The probability of offspring with cystic fibrosis when two heterozygous individuals mate is 25%.

• Application of Genetics in Disease

  • Understanding genetic contributions to human diseases (e.g., heart disease, diabetes) can lead to personalized medicine and preventive measures via genetic testing and intervention strategies.

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