Genetics: Punnett Squares and Pedigrees

Punnett Squares and Pedigrees

• Punnett squares are used to predict the possible genotypes and phenotypes of offspring from parents with known genotypes.
• Pedigrees are diagrams that trace the inheritance of a trait through generations of a family. They show affected individuals, carriers, and unaffected individuals.

Gregor Mendel's Laws of Inheritance

• Mendel's work with pea plants revealed fundamental laws of inheritance.
• Dominant traits appear more frequently than recessive traits.
• Recessive traits require both alleles to be present for expression.
• Sex-linked traits are controlled by genes on sex chromosomes (X or Y).
• Codominance occurs when both alleles are fully expressed together.
• Incomplete dominance occurs when both alleles are partially expressed.
• Multiple alleles means a single gene has more than one allele.
• Polygenic inheritance occurs when multiple genes influence a phenotype.
• Phenotype refers to observable characteristics, while genotype refers to the genetic makeup.
• Heterozygous genotypes have two different alleles, while homozygous genotypes have two identical alleles.

Chromosomes and Meiosis

• The law of segregation states that alleles separate during gamete formation.
• The law of independent assortment states that genes for different traits assort independently.
• Law of dominance - one of the pairs of inherited traits will be dominant and the others recessive unless both factors are recessive
• Duplication - a section of the chromosome is copied and inserted into the genome.
• Deletion - a section of the chromosome is lost or deleted.
• Inversion - a section of the chromosome breaks off, flips around, and reattaches in the reverse order.
• Translocation - section of one chromosome breaks off and reattaches to another chromosome
• Nondisjunction- homologous chromosomes don't separate so both chromosomes of the pair pass to the daughter cell.
• Examples of nondisjunction syndromes: Down syndrome (trisomy 21), Klinefelter syndrome (XXY), Turner syndrome (monosomy X).

DNA

• DNA structure:
  • DNA is a double-helix polymer.
  • Two strands wound around each other.
  • Bases pair A-T and C-G
• Chargoff's rules:
  • The amounts of thymine and adenine are identical in any DNA molecule.
  • The amounts of thymine and guanine differ in DNA in different species.
• DNA functions:
  • Stores genetic information.

Gene Expression

• Gene expression:
  • Starts in nucleus: DNA copied to mRNA.
  • mRNA travels to ribosomes
  • Ribosomes translate mRNA into proteins.
  • Types of mutations: base pair substitutions (missense, nonsense, silent, and neutral).
  • Insertion and deletion (frameshifts).
• DNA proofreading and repair mechanisms correct errors during DNA replication.

Biotechnology

• Genetic engineering: Alters the genes of an organism.
• Gene therapy: Modifies genes to treat diseases.
• Cloning: Creates genetically identical copies.
• 3 bioprinting - uses cells and biomaterials to create tissue-like structures, medical research.
• GMOs - genetically modified organisms, creates food crops with desirable traits, including yield and nutrition.
• Biofuels: Alternative energy sources (algae-based).

Recombinant DNA

• Recombinant DNA technology combines DNA from different organisms to produce benefits.

Ethics

• The human genome project aimed to map and understand all human genes.

Meiosis

• Meiosis is a type of cell division that produces gametes (sex cells).
• Meiosis I and II each consist of four phases (prophase, metaphase, anaphase, and telophase), resulting in four non-identical haploid daughter cells from one original diploid cell.
• The processes reduce chromosome number for sexual reproduction and increase genetic variability.