Principles of Inheritance and Variation

• Mendelian Laws:

  • Law of Segregation: Each parent contributes one copy of each gene to their offspring. Visualized using Punnet Squares.
  • Law of Independent Assortment: Genes on different chromosomes assort independently of one another.

• Incomplete Dominance:

• Codominance: Both alleles of a gene are expressed in the heterozygous condition, resulting in a distinct phenotype. Example: Red and white flower colors in snapdragons giving rise to pink flowers.

• Multiple Alleles: Multiple forms of a gene can exist within a population, leading to variations in traits.

  • ABO Blood Group System: Example of multiple alleles with A, B, and O alleles determining blood types.

• Sex Determination:

  • Sex Chromosomes: X and Y chromosomes determine the sex of an individual.
  • Sex-linked Inheritance: Genes located on sex chromosomes exhibit unique inheritance patterns.

• Linkage and Recombination:

  • Linkage Groups: Genes that are located close together on the same chromosome tend to be inherited together.
  • Recombination Frequency: Measure of how often linked genes are separated during crossing over, providing a tool to map gene locations on chromosomes.
  • Crossing Over: Process during meiosis where chromosomes exchange genetic material, leading to genetic diversity.

• Variations:

  • Genetic Variation: Differences in genes within individuals or populations.
  • Sources of Variation: Mutations, genetic recombination, and random mating contribute to genetic variation.

• Mutation:

  • Types of Mutations: Mutations can involve gene alterations, chromosome aberrations, or changes in chromosome number.
  • Causes of Mutations: Environmental factors like radiation and chemicals, errors during DNA replication, and viral infections can lead to mutations.

• DNA Replication:

  • Semi-Conservative Replication: Each DNA strand serves as a template to synthesize a new complementary strand, resulting in two identical copies of the original DNA.
  • Enzymes involved in Replication: Enzymes such as DNA polymerase, helicase, and ligase play crucial roles in DNA replication.

• Transcription:

  • Transcription Unit: Region of DNA that contains the instructions for making an RNA molecule.
  • RNA Polymerase: Enzyme that synthesizes RNA molecules using DNA as a template.
  • Types of RNA: Includes messenger RNA (mRNA), ribosomal RNA (rRNA), and transfer RNA (tRNA).

• Translation:

  • Genetic Code: Specific sequences of nucleotides on mRNA that code for particular amino acids.
  • Ribosomes: Cellular structures responsible for protein synthesis, composed of rRNA and proteins.
  • Protein Synthesis: Process by which mRNA is translated into a sequence of amino acids, forming proteins.

• Gene Expression:

• Regulation of Gene Expression: Various mechanisms, such as transcription factors, control when and where genes are expressed.

• Evolution:

  • Origin of Life: Theories explore how simple molecules gave rise to complex living organisms.
  • Natural Selection: Process by which individuals better adapted to their environment have a higher chance of survival and reproduction, leading to changes in species over time.
  • Adaptive Radiation: Divergence of species from a common ancestor into diverse forms adapted to different environments.
  • Convergent Evolution: Independent evolution of similar traits in different species due to similar environmental pressures.
  • Divergent Evolution: Gradual accumulation of differences between populations over time, leading to the formation of new species.