General ---------Biology----------------------------------------------------- ------------------Online------------------------------------------------------------ Ch. 14 Mendel and the Gene Idea

In Chapter 12 (mitosis) we saw how chromosomes duplicated in the S Phase of interphase, and how they coiled up, separate and reformed in the nuclei of the new daughter cells.  This was mitosis, the mechanism of asexual reproduction.  Asexual reproduction produces clones; individuals genetically identical to the parent.

In Ch. 13 (meiosis) we saw how cells in germ tissue (ovaries and testes) duplicate and divide their chromosomes to form gametes and how fertilization produces offspring with vastly different genetic combinations that their parents. 

This Ch. 14 we will see how the individual genes on chromosomes are sorted into gametes and combined in fertilization to produce their traits in individuals.  To do this we will observe how traits move from one generation to the next.  For example, we will look at hemophilia in several generations of european royalty.  To be able to predict if the children of descendants of these royal families will have the disease, we need to understand how chromosomes behave when they form gametes, how fertilization brings the chromosomes of two individuals together, and how the genes in this new genetically unique individual express themselves.

Ch. 14 begins with a discussion of Gregor Mendel, a monk who lived in the middle 1800's.  Mendel got the idea that inheritance was carried in individual packets; he coined the word "genes."  At this time, scientists had only primitive microscopes and no knowledge of the internal structure of cells, much less the existence of chromosomes.  Mendel made his discovery by looking at several generations of garden peas and reasoning that parental genes must be passed to offspring as discrete units, or genes.  He also reasoned that each individual must contain two copies of each gene, and that these copies could separate from each other and sort themselves into different gametes.