Inheritance, Variation, and Evolution

Sexual Reproduction

• Gametes or sex cells are produced via meiosis.
  • Example: In testes to produce sperm.
  • Chromosomes in a diploid cell (23 pairs for humans) are copied.
  • Similar chromosomes pair up and swap genes.
  • Cell divides to form two diploid cells, then divides again to form four haploid cells.
  • Haploid cells are ready to fuse with another gamete (e.g., an egg).
• Variation occurs in offspring due to gene shuffling.
• After fertilization, the diploid cell divides by mitosis to grow.

Asexual Reproduction

• Involves no gametes; results in genetically identical offspring (clones).
• Advantages:
  • Only one parent needed.
  • Useful for species survival in isolated conditions.
• Examples: Certain plants, parasites like malaria, and some fungi.

DNA and Genetics

• Genome: Total genetic material in an organism.
• DNA Structure: Double helix polymer; genes code for proteins.
• Human Genome Project: Mapped all human genes by 2003.
• Genotype vs. Phenotype:
  • Genotype: Genetic code.
  • Phenotype: Expression of genotype in characteristics.
• Nucleotides: Composed of sugar, phosphate, and base (A, T, C, G).
  • A pairs with T, C pairs with G.
• Protein Synthesis:
  • mRNA transcribes DNA sequence and moves to ribosome.
  • Amino acids are assembled into proteins.
• Mutations: Can alter genes, potentially leading to non-functional proteins.
• Epigenetics: Study of how DNA can be influenced by environmental factors.

Genetic Inheritance

• Alleles: Different forms of a gene (e.g., color blindness).
• Dominant vs. Recessive Alleles:
  • Dominant alleles express the trait even with another allele present.
  • Recessive traits express only with two recessive alleles.
• Homozygous vs. Heterozygous Alleles:
  • Homozygous: Two identical alleles (BB or bb).
  • Heterozygous: Two different alleles (Bb).
• Punnett Squares: Used to predict genotype and phenotype probabilities.

Sex Determination

• 23 pairs of chromosomes in humans; 1 pair determines sex.
• XX = Female, XY = Male.

Evolution

• Darwin's Theory: Random variation leads to better adaptation to environments.
• Epigenetic Influence: DNA can activate or deactivate genes based on environmental needs.
• Example: Blind, translucent fish gaining eyes when exposed to light.

Bacterial Resistance and Selective Breeding

• Antibiotic Resistance: Result of mutation and natural selection in bacteria.
• Selective Breeding: Used to enhance desired traits in organisms.
• Genetic Modification:
  • Bacteria produce insulin.
  • Crops modified for better yield or nutritional value.

Cloning and Fossils

• Cloning:
  • Easy in plants (cuttings or tissue culture).
  • Complex in animals (nuclear transfer).
• Fossils: Preserved remains/traces of ancient organisms.
  • Formed through mineral replacement or lack of decay conditions.

Classification

• Hierarchy: Kingdom, Phylum, Class, Order, Family, Genus, Species.
• Domains: Archaea, Bacteria, Eukarya.
• Eukaryotic Cells: Possess DNA within a nucleus.
• Extremophiles: Archaea living in extreme environments.