Introduction to Heredity and Mendelian Genetics

Introduction to Heredity

• Heredity is the passing of traits from parents to offspring.
• These traits are determined by genes, which are segments of DNA.
• Genes carry the instructions for building and maintaining an organism.
• The process of passing genetic information from one generation to the next is central to all life forms.

Mendelian Genetics

• Gregor Mendel, through his experiments with pea plants, established the basic principles of heredity.
• Mendel's Laws describe how traits are inherited.
• The Law of Segregation states that each parent contributes one allele for a trait to their offspring.
• The Law of Independent Assortment states that different traits are inherited independently of each other.
• Alleles are different forms of a gene.
• Dominant alleles mask the expression of recessive alleles when both are present.
• Genotype refers to the genetic makeup of an organism.
• Phenotype refers to the observable physical traits of an organism.

Types of Inheritance

• Monohybrid cross: A cross between parents that differ in only one trait.
• Dihybrid cross: A cross between parents that differ in two traits.
• Incomplete dominance: neither allele is completely dominant over the other, with the heterozygote expressing an intermediate phenotype (e.g., red and white flowers producing pink flowers).
• Codominance: both alleles are expressed equally in the heterozygote (e.g., AB blood type).
• Multiple alleles: A gene can have more than two alleles (e.g., human blood type).
• Polygenic inheritance: several genes influence a single trait (e.g., human height).
• Sex-linked inheritance: genes located on the sex chromosomes (e.g., color blindness).
• Sex-limited traits are traits that are present in both sexes but are expressed only in one (e.g., milk production in mammals).
• Sex-influenced traits are traits whose expression differs in males and females.

Chromosomes and Genes

• Chromosomes are thread-like structures found in the nucleus of cells.
• Humans have 23 pairs of chromosomes.
• Chromosomes are made up of DNA.
• Genes are located on specific positions (loci) on chromosomes.

Gene Mutations

• Mutations are changes in the DNA sequence of a gene.
• Mutations can be caused by errors during DNA replication or by environmental factors (mutagens).
• Mutations can be beneficial, neutral, or harmful, depending on their effect on the organism.

Genetic Disorders

• Genetic disorders are caused by mutations in genes.
• Some common genetic disorders include cystic fibrosis, sickle cell anemia, and Huntington's disease.
• These disorders can affect various aspects of health, from physical function to development.
• Genetic counseling can help families understand, assess, and cope with the risk of genetic disorders.

DNA Structure & Function

• DNA is a double helix shaped molecule.
• The backbone of DNA is composed of sugar and phosphate molecules.
• The rungs of the DNA ladder are composed of nitrogenous bases paired together (A with T and G with C).
• DNA carries the genetic instructions for building proteins, and all cells and biological processes.
• RNA is a single-stranded nucleic acid that plays a crucial role in protein synthesis.