Non-Mendelian Genetics Overview

Non-Mendelian Genetics

  • Complex Inheritance Patterns
    • Non-Mendelian genetics refers to inheritance patterns that do not follow Mendelian laws.

Learning Objectives

  • Understand non-Mendelian genetics and its various patterns of inheritance.
  • Expand knowledge of alleles and their functions.

Review of Mendel's Laws

  • Law of Dominance
    • Dominant alleles are expressed over recessive alleles.
  • Law of Segregation
    • Organisms inherit two copies of each gene (alleles) from their parents.
  • Law of Independent Assortment
    • Genes for different traits are sorted independently during gamete formation.

Exceptions to Mendel's Laws

  • Some alleles are neither dominant nor recessive.
  • Many traits are controlled by multiple alleles or genes.
  • Examples of traits not following Mendel’s laws can be diverse based on individual genetics.

Incomplete Dominance

  • Definition
    • No allele is dominant or recessive. Both alleles are expressed simultaneously, leading to a heterozygous phenotype that is a mix of both traits.
  • Example
    • Red flower (R) crossed with White flower (W) = Pink flower (RW).

Practice Problem on Incomplete Dominance

  • Cross
    • Red flower (RR) x Yellow flower (YY).
  • Genotypic and Phenotypic Ratios - To be calculated by student.

Codominance

  • Definition
    • Both traits are fully expressed. Both alleles contribute equally to the phenotype.
  • Examples
    • Red + White flower = Red and White flower.
    • Blood types exhibit codominance (A, B, AB types).

Practice Problem on Codominance

  • Horses Example
    • Cross between a white horse (WW) and an appaloosa horse (BB) = determine genotypic and phenotypic probabilities.

Multiple Alleles

  • Definition
    • More than one allele exists for a given gene.
  • Example
    • Blood types A, B, O (shown as i).
    • Hair color in rabbits can have multiple alleles leading to varied phenotypes.

Practice Problem on Multiple Alleles

  • Cross
    • Dark grey rabbit (Ccch) x Himalayan rabbit (chc).
  • Phenotypes
    • Dark grey (C), Chinchilla (cch), Himalayan (ch), White (c).

Linked Genes

  • Definition
    • Genes physically located on the same chromosome that tend to be inherited together.
  • Inheritance Note
    • Linked genes do not assort independently.

Chromosome Types

  • Autosomal Chromosomes
    • 22 pairs are similar for males and females, containing genes affecting traits.
  • Sex Chromosomes
    • Pair 23 determines sex (XX = female, XY = male).
    • X chromosome carries many genes while Y carries fewer.
  • Sex-Linked Traits
    • Traits associated with genes on sex chromosomes; carriers may carry recessive traits without expressing them.

Practice Problem on Sex-Linked Traits

  • Colorblindness Example
    • Colorblindness is an X-linked recessive trait (XB normal vision, Xb colorblind).
    • Cross a carrier female (XBXb) with a normal male (XY).
  • Genotypic and Phenotypic Probabilities - To be calculated by student.