Sexual Sources Of Genetic Variation

Independent Assortment of Chromosomes

  1. Occurs during Metaphase I
  2. There is a 50-50 chance that a chromosome will pair with another paternal/maternal chromosome.



  1. Sometimes the linkage seemed to break, but only between homologous pairs of chromosomes.
  2. This genetic recombination is called crossover.
  3. The farther apart genes are the greater the chance of crossover.
  4. By examining frequency of crossover, the relative distance of genes was mapped.


Random Fertilization

  1. The that sperm actually fertilizes an ovum is a random selection.
  2. A human ovum can have one of 8 million chromosome combinations.
  3. An individual human sperm can have of 8 million different chromosome combinations.
  4. This yields 64 trillion possible combinations minimum.