Introduction to Heredity and Mendelian Genetics

Introduction to Heredity

• Heredity is the passing of traits from parents to offspring.
• Traits can be physical characteristics (like eye color) or behaviors (like temperament).
• The fundamental unit of heredity is the gene.
• Genes are segments of DNA that code for specific proteins.
• These proteins determine various traits.

Principles of Mendelian Genetics

• Gregor Mendel's experiments with pea plants established fundamental principles of inheritance.
• Mendel's work demonstrated that traits are passed from parents to offspring in predictable patterns.
• Law of Segregation: During gamete formation, the two alleles for each trait separate, and each gamete receives only one allele.
• Law of Independent Assortment: Alleles of different genes segregate independently of one another during gamete formation. This means the inheritance of one trait doesn't influence the inheritance of another.

Types of Inheritance Patterns

• Dominant-Recessive: One allele (dominant) masks the expression of another allele (recessive).
• Incomplete Dominance: The heterozygous phenotype is an intermediate blend of the two homozygous phenotypes.
• Codominance: Both alleles are expressed in the heterozygous phenotype.
• Multiple Alleles: A gene can have more than two alleles. Blood type is an example.

Chromosomes and Inheritance

• Chromosomes carry the genetic information (DNA).
• Humans have 23 pairs of chromosomes.
• One set of chromosomes comes from each parent.
• Sex chromosomes (X and Y) determine the sex of an individual.
• Autosomes are non-sex chromosomes.

Sex-Linked Inheritance

• Sex-linked traits are determined by genes located on the sex chromosomes (usually the X chromosome).
• Examples of sex-linked traits include color blindness and hemophilia.
• Males are more likely to express sex-linked recessive traits because they have only one X chromosome.

Non-Mendelian Inheritance

• Epistasis: One gene affects the expression of another gene.
• Polygenic Inheritance: Several genes contribute to a single trait, like height or skin color.
• Pleiotropy: A single gene can affect multiple traits.
• Environmental Influence: Environmental factors can affect the expression of genes (e.g., nutrition, stress, temperature). The environment interacts with genetics to determine the phenotype.

Modern Genetic Concepts

• The Human Genome Project mapped the entire human genome, determining the sequences of bases in DNA.
• Genetic engineering and biotechnology utilize new techniques to manipulate genes.
• Molecular genetics examines the structure and function of genes at a molecular level.
• Genetic technologies like CRISPR are used for gene editing.

Genetic Disorders

• Genetic disorders arise from mutations in genes and can result from various sources (e.g., errors in DNA replication, exposure to mutagens).
• Examples of genetic disorders include cystic fibrosis, sickle cell anemia, and Huntington's disease.
• Genetic counseling provides information and support for individuals concerned about genetic risks for themselves or their families.
• Genetic testing can identify potential genetic diseases and risks.

Heredity and Evolution

• Heredity is fundamental to the process of evolution.
• Mutations provide the raw material for natural selection and adaptation.
• Changes in gene frequencies within populations over time lead to evolutionary changes.