MENDELIAN GENETICS

• Outcome 3-Explain the Genetic Basis of Heredity and apply Patterns of Mendelian Inheritance
• Aims and Objectives: Apply Mendel's laws to solve genetic problems including monohybrid crosses and dihybrid crosses
• Law of Segregation


  Individuals possess two alleles for a trait and a parent passes only one allele to his/her offspring
• Law of Independent Assortment

  The alleles of two (or more) different genes get sorted into gametes independently of one another
• Law of Dominance


  In a heterozygote, one trait will conceal the presence of another trait for the same characteristic. The dominant allele will be expressed exclusively.
• Gregor Mendel was an Austrian Monk that lived in the 1800s. He carried out studies with pea plants to see how traits were passed from one generation to the next. He became known as the father of genetics for identifying the basic rules of inheritance.
• Monohybrid Cross


  A cross between two individuals who have different alleles for a trait

  
• Monohybrid Cross


  • Tongue rolling ability occurs due to the influence of a dominant allele. A person who has either one or two copies of the dominant allele (T) will be able to twist their tongue.
• Monohybrid Cross


  1. Assume one parent is homozygous dominant for tongue twisting and one is homozygous recessive

  2. Complete the punnett square

  3. Determine the genotype/s of the children

  4. Determine the phenotype/s of the children

  
• Monohybrid Cross


  1. Assume two heterozygous tongue twisters are crossed

  2. Complete the punnett square

  3. Determine the possible genotype/s of the children

  4. Determine the phenotype/s of the children

  
• Dihybrid Cross


  A cross between two individuals with two observed traits that are controlled by two distinct genes

  
• Dihybrid Cross


  • In sheep, the allele for black wool (B) is dominant over the allele for white wool (b)
  • The allele for horns (H) is dominant over the allele for being hornless (h)
• Dihybrid Cross


  1. Cross pure breeding horned sheep with black wool and pure breeding hornless sheep with white wool

  2. Determine the genotype and phenotype of the F1 individuals

  3. Cross two of the F1 offspring (BbHh x BbHh)

  4. Calculate the expected ratio and percent of phenotypes in the F2 generation
• To summarise, we can ascertain the inheritance of a trait controlled by a single gene using a monohybrid cross, and the inheritance of two traits controlled by independent genes using a dihybrid cross.