Genetics

• What is genetics?

  • Genetics is the scientific study of heredity
• The CRISPR-Cas9 system is a genome editing tool that uses a protein called Cas9 to cut DNA at a specific location

  
• The Cas9 protein is guided to the target DNA by a short piece of RNA called a guide RNA, designed to match the DNA sequence at the target site
• When the Cas9 protein binds to the guide RNA, it unwinds the DNA and cuts it at the target site, creating a double-stranded break that can be repaired by the cell's natural DNA repair mechanisms
• Components of the CRISPR-Cas9 system include the Cas9 protein, guide RNA, and a PAM sequence necessary for Cas9 binding

  
• Therapeutic outcomes following DNA cleavage by Cas9 can be repaired by non-homologous end joining (NHEJ) or homology-directed repair (HDR)
• Lamarck's theory of evolution proposed the inheritance of acquired characteristics, later disproven by Darwin's theory of evolution by natural selection
• Mendel, the father of Genetics, conducted experiments with pea plants, discovering principles like particulate inheritance and the Law of Segregation
• Mendel's experiments showed that physical traits are inherited as "particles," which we now know as chromosomes and DNA
• Mendel concluded that biological inheritance is determined by factors passed from generation to generation, known as genes with alternative forms called alleles
• Mendel's Law of Dominance states that some alleles are dominant, and others are recessive
• Mendel's Law of Segregation explains how alleles for traits are separated during the formation of sex cells
• Mendel's Theory of Segregation states that for each inherited characteristic, an organism has two genes, one from each parent
• Genotype refers to the gene combination for a trait, with homozygous genotypes involving 2 dominant or 2 recessive genes, and heterozygous genotypes involving one dominant and one recessive allele
• A Punnett square is a diagram showing the probability of a trait being passed from one generation to another
• Probability principles can be used to explain genetic crosses, with alleles segregating randomly like a coin flip
• A test cross is a method to figure out the genotype of an organism by crossing it with a known homozygous recessive individual
• Monohybrid genetic crosses involve traits controlled by a single gene, while dihybrid genetic crosses involve traits controlled by two genes
• The Law of Independent Assortment states that during gamete formation, segregating pairs of unit factors assort independently of each other
• Endocrine glands include the pituitary gland, thyroid gland, parathyroid glands, adrenal glands (including the adrenal medulla), pancreas, ovaries/testes, and pineal gland.
• Exceptions to Mendel’s principles


  • Some alleles are neither dominant nor recessive
  • Many traits are controlled by more than one gene (polygenic traits)
  • Prevalent alleles in a population are termed wild-type alleles
  • Alleles that have been altered by mutation are termed mutant alleles
  • Loss of Function
  • Gain of Function
  • Neutral Mutation
• Independent Assortment

  Alleles separate independently during the formation of gametes
• Roan Cattle Inheritance (Codominance)

  • Color of hair coat in cattle
• Dominance Relations


  • Various ways in which a pair of alleles can affect the phenotype
  • Alleles can show different degrees of dominance and recessiveness in relation to each other
  • Incomplete Dominance
  • Co-dominance
• Mendelian Laws


  Principles of inheritance discovered by Gregor Mendel
• Red flower crossed with white flower

  All offspring are pink
• Multiple allele inheritance occurs when two or more alleles are present
• Dihybrid cross


  Breeding experiment tracking the inheritance of two traits
• Extension of Mendelian Genetics

  Further exploration of genetic inheritance based on Mendel's principles
• Mendel’s “Law of Independent Assortment”


  Each pair of alleles segregates independently during gamete formation
• Japanese four-o-clock flowers

  • Red flower plant genotype = RR
  • White flower plant genotype = WW
  • Pink flower plant genotype = RW
• Asian flower Camellia

  • Exhibits codominance in the form of white spots
• F1 cross to produce the F2 generation


  Offspring would all be hybrid for both traits (RrYy)
• Incomplete Dominance


  Neither allele is dominant, resulting in a blend of each allele in the phenotype
• Codominance


  When two alleles both appear in the phenotype, usually signified using superscripts
• Red snapdragon crossed with white snapdragon

  Resulting offspring will all be pink
• Two-factor cross


  • Shape and Color of peas
• Human Blood Type A

  • Allele - IA
  • Blood cells have small antigens on the surface
• Human Blood Types


  • A
  • B
  • AB
  • O
• Multiple Allele Inheritance


  • When two or more alleles contribute to the phenotype