Genetics Heredity

• Genetics - the scientific study of heredity.
• Heredity - the passing of physical characteristics from parents to offspring.
• DNA - contains your genes; found in the nucleus.
• Genes - the factor that controls a trait; found on chromosomes.
• Traits - the different forms of a characteristic (ex. dimples: present or absent).
• Alleles - the letters that represent the different forms of a gene (dimples: D = present; d = absent).
• Dominant - the traits that overshadows and is expressed (capital letter).
• Recessive - the trait that hides in the background (lowercase letter).
• Genotype - combination of alleles (such as DD, Dd, dd).
• Phenotype - the physical appearance of a trait (ex. dimples or no dimples).
• Homozygous - two alleles/letters for one trait that are the same (ex:  DD or dd).
• Heterozygous - two alleles/letters for one trait that are different (ex. Dd).
• Gregor Johann Mendel:

  • Austrian monk and math & science teacher.
  • He discovered the principles of heredity while studying garden pea plants.
  • Mendel’s experiments with peas led him to being named the “FATHER OF GENETICS.”
• Mendel chose to study peas because they can self-pollinate or cross pollinate. 
• This means a pea plant can produce offspring by itself to create a purebred (or true-breeding plant) with identical traits or a pea can cross with another pea plant to produce offspring with mixed traits from both parent plants.
• Mendel studied 7 traits of pea plants, but only studied ONE trait at a time.
• For example, to see how height was passed from parent to offspring, Mendel took pollen from a true-breeding tall pea plant and cross-pollinated it with a true-breeding short pea plant.
• This formed a hybrid: offspring of parents that have different forms of a trait.
• Mendel crossed plants with different traits and found that some traits showed up more often – dominant traits, while other traits didn’t show up again until later generations –recessive traits.
• For each of the 7 traits that Mendel studied in peas, there is a dominant allele and a recessive allele.
• If a plant inherits both a dominant allele and a recessive allele (hybrid), the dominant allele masks the recessive allele.
• Two Mendel's Laws of Heredity:

  1. Law of Segregation
  2. Law of Independent Assortment
• Law of Segregation - every organism has two alleles of each gene and when gametes (sex cells) are produced, the alleles separate.  
• Law of Independent Assortment - genes for different traits are inherited separately from each other.
• 7 Traits of the Pea Plant:

  1. Flower Color
  2. Flower Position
  3. Seed Color
  4. Seed Shape
  5. Pod Shape
  6. Pod Color
  7. Stem Length
• Punnett Squares - created by Reginald Punnett to predict the probability and possible genotypes in offspring. 
• Probability:

  • the likelihood that a particular event will occur.
  • determines what is likely to occur, not what does occur.