Evolution and Genetics

Understanding Cells

• Robert Hooke (1665): Observed "small rooms" in cork and termed them cellula.
• Cells: The smallest living biological structures and the basic units of life.
• Prokaryotes/prokaryotic:
  • Single-celled organisms (e.g., bacteria, blue-green algae).
  • Originated 3.7 billion to 4+ billion years ago.
• Eukaryotes/eukaryotic:
  • Single- or multi-celled organisms (e.g., plants, birds, mammals, reptiles).
  • Originated 1.2 billion years ago; more complex forms 600-800 million years ago.

Eukaryotic Cells: A Closer Look

• Organelles: Structures within eukaryotic cells.
  • Nucleus: Control center of the cell; contains DNA and RNA.
  • Mitochondria: Power plant of the cell; contains mtDNA.
  • Ribosomes: Create protein within the cell.

Types of Cells

• Somatic cells:
  • Tissue cells (hair, skin, muscle, cilia, etc.).
  • Structural.
• Gametes:
  • Sperm + egg cell = zygote.
  • Transmit genetic information.

DNA: The Universal Code

• Deoxyribonucleic acid: Contains genetic material that directs cell development and function.
• Organisms differ in arrangement and regulation of their DNA.
• Main function: to direct protein production (protein synthesis).
• Information in DNA is stored as a code made up of 4 chemical bases:
  • Adenine (A), Thymine (T), Cytosine (C), Guanine (G).
  • Organization of bases dictates development and function; they bond in a complementary way (A-T, C-G).
• Nucleotide chain = base + sugar + phosphate.
• Double helix: spiral of nucleotide chains.

DNA Replication

• Growth, development, and repair require cells to replicate.
• Enzymes sever bonds between base pairs → bases attract unattached DNA nucleotides within the cell nucleus.
• The result is two double-stranded DNA molecules.

Proteins

• Types of proteins: structural, binders, hormones, enzymes, regulatory.
• Examples: collagen, hemoglobin, lactase, insulin.

Amino Acids

• Amino acids: building blocks of protein.
• DNA specifies the type of amino acid by arranging chemical bases (A, T, C, and G) into groups of 3 (triplet/codon).

Protein Synthesis: Transcription

• Genetic information is transcribed/copied onto mRNA in the nucleus (messenger RNA).
• RNA polymerase binds to DNA.
• RNA polymerase separates strands of DNA to expose bases, reads bases to make mRNA strand.
• Bases on mRNA strand (template) organize into groups of 3 (triplet/codon) that code for a specific amino acid.
• mRNA template leaves the nucleus → ribosomes.
• DNA vs. RNA:
  • DNA: Bigger in size, double-stranded, contains thymine (T).
  • RNA: Smaller in size, single-stranded, contains uracil (U).

Protein Synthesis: Translation

• mRNA travels to ribosomes.
• mRNA binds to tRNA (transfer RNA).
• tRNA forms chains of amino acids by binding/folding to form proteins.

Genes

• Unit of heredity.
• Sequences of DNA bases that specify or identify the order of amino acids for a protein, part of a protein, or another functional product.
• Genome: genetic makeup of an organism.
  • Contains information to build and maintain cells.
  • Controls expression, inheritance, and evolution of biological traits.

Chromosomes

• Strands of DNA found within the nucleus.
• Carry information on cell function and heredity.
• Number depends on species (humans have 46 chromosomes, arranged in 23 pairs).
  • Autosomes: carry genetic information for physical characteristics. Humans have 22 pairs of autosomes + 1 pair of sex chromosomes, inheriting one of each pair from each parent.
  • Sex chromosomes.
• Locus: place/position of a gene on a chromosome.
• Allele: alternative form of a gene.

Cell Division

• Mitosis: Occurs during growth, aging, and injury in somatic cells; produces new cells.
• Meiosis: Produces new individuals.

Heredity and the Contributions of Gregor Mendel (1822 – 1884)

• Charles Darwin: blended inheritance.
• Mendel’s experiments on pea plants:
  • Offspring are not blended.
  • Offspring follow a predictable pattern in the expression of traits (“factors”).
  • Dominant/recessive.
  • Homozygous/heterozygous.
• Alleles.
• Dominant alleles.

Punnett Squares

• Used to predict the genotypes and phenotypes of offspring.
• Example: Pea pod color, where green is dominant and yellow is recessive.
• Genotype: Genetic makeup (e.g., CC, Cc, cc).
• Phenotype: Observable characteristics (e.g., green or yellow pea pods).

Mendelian Inheritance

• Discrete traits: controlled by alleles at a single locus.
  • Dominant trait conditions: e.g., achondroplasia (dwarfism), Marfan syndrome, Huntington disease.
  • Recessive trait conditions: e.g., cystic fibrosis, Tay-Sachs disease, sickle-cell anemia.
  • ABO blood group system: A and B are codominant; 0 is recessive.
• Examples: albinism, cleft chin, hypodontia of lateral incisors.

Mendelian vs. Non-Mendelian Traits

• Mendelian Traits:
  • Influenced by a single genetic locus.
  • Traits are discrete and less complex.
  • Less environmental influence on gene expression.
  • Few phenotypes are possible.
• Polygenic Traits:
  • Influenced by +2 genetic loci.
  • Continuous traits are more complex.
  • Environmental influence on gene expression is possible.
  • Many phenotypes are possible.

Evolutionary Processes

• Mutation:
  • Change, variation in DNA from original sequence.
  • Can occur in response to environmental conditions or replication error.
  • Source of new variation in a population.
  • Must occur in a gamete to be evolutionarily significant.
• Selection:
  • Natural selection: Organisms that are better adapted to their environment are more likely to survive and contribute genetic material to subsequent generations.
  • Artificial selection: Humans selectively breed for desirable traits; some are beneficial, others are not.
  • Sexual selection: Selection for features/behaviors associated with mating (e.g., female choice).
• Gene flow:
  • Interchange of genes between populations.
  • Individuals mate in a new population but don’t necessarily stay there.
• Genetic drift:
  • Random, occurs in small populations.
  • Alleles become more/less prevalent.
    • Founder Effect:
      • Occurs when a small group establishes a new population in a new area/colonization.
      • Restricted representation of alleles in the founding group due to genetic bottleneck = reduced genetic variation.
      • Rare alleles can become more common.
      • The population can become genetically distinct over time.

Modern Evolutionary Theory, Micro/Macroevolution

• Evolution:
  • A change in allele frequency from one generation to the next.
  • A two-step process:
    • Production and distribution of variation.
    • Natural selection acting on this variation.
• Microevolution: change at the microscopic level.
• Macroevolution: results in the formation of new species.