The Nature of Heredity

• Chromosomes are found in the nucleus of all eukaryotic cells
• Chromosomes vary widely between organisms of different species in their number, shape, and size
• Most chromosomes are found in sets (diploid), for example, humans have 2 sets of 23 chromosomes in body cells
• Haploid cells have half the normal number of chromosomes
• Polyploids contain three or more sets of chromosomes, and many plants are polyploids
• Asexual reproduction:

  • New individual is produced from a single parent cell by cell division, genetically identical to the parent
• Advantages of asexual reproduction:

  • Parent does not have to seek out a mate
  • Does not perform specialized mating behaviors
  • Lacks specialized anatomy
• Disadvantages of asexual reproduction:

  • Lacks diversity, leading to decreased genetic variability
• Sexual reproduction:

  • Individuals are produced by the fusion of two sex cells, genetically different from either parent
• Advantages of sexual reproduction:

  • Increased genetic variability
• Disadvantages of sexual reproduction:

  • Energy and resources required for generation/protection of sex cells
  • Difficulties surrounding fertilization, such as special characteristics or behaviors (antlers, showy flowers, mating behaviors) that may increase the chances of predation
• Summary:

  • Genetic information is stored in DNA molecules within the chromosomes of cells
  • Genes, which carry heritable information, are found at distinct locations on a chromosome
  • Chromosome number, shape, and size vary from species to species
  • Asexual reproduction results in offspring that are genetically identical to their single parent
  • Sexual reproduction results in offspring that are genetically variable, inheriting half of their genetic information from each of two parents