Reproduction is a property associated with life. The fact that organisms reproduce their own kind is a consequence of heredity.

Heredity - Continuity of biological traits from one generation to the next.
  • Results from the transmission of hereditary units, or genes, from parents to offspring
  • Because they share similar genes, offspring more closely resemble their parents or close relatives than unrelated individuals of the same species.
Variation - Inherited differences among individuals of the same species.
  • Though offspring resemble their parents and siblings, they also diverge somewhat as a consequence of inherited differences among them.
  • The development of genetics in this century has increased our understanding about the mechanisms of variation and heredity.
Genetics - the scientific study of heredity and variation.

Offspring acquire genes from parents by inheriting chromosomes.
DNA - Type of nucleic acid that is a polymer of four different kinds of nucleotides.

Genes - Units of hereditary information that are made of DNA and are located on chromosomes.
  • Have specific sequences of nucleotides, the monomers of DNA
  • Most genes program cells to synthesize specific proteins; the action of these proteins produce an organism's inherited traits.

Inheritance is possible because:
  • DNA is precisely replicated producing copies of genes that can be passed along from parents to offspring.
  • Sperm and ova carrying each parent's genes are combined in the nucleus of the fertilized egg.
The actual transmission of genes from parents to offspring depends on the behavior of chromosomes.

Chromosomes - Threadlike structures in eukaryotic muclei that are made of DNA and proteins
  • Consist of a single long DNA molecule that is highly folded and coiled along with proteins
  • Contain genetic information arranged in a linear sequence
  • Contain hundreds of thousands of genes, each of which is a specific region of the DNA molecule; or locus.
  • Each species has a characteristic chromosome number; humans have 46.

Like begets like, more or less: a comparison of asexual versus sexual reproduction
asexual_sexual_reproduction.png
What generates this genetic variation during sexual reproduction? The answer lies in the process of Meiosis.