Mendel and the Gene Idea

Vocabulary for 14.1  Character- A heritable feature that varies among individuals.  Trait- Each variant for a character  Hybridization- The mating or crossing of two true breeding varieties.  P generation- The parent individuals from which offspring are derived in studies of inheritance.  F1 generation- First filial or hybrid offspring in a series of genetic crosses.  F2 generation- Offspring resulting from interbreeding of the hybrid F1 generation.

Drawing from the Deck of Genes  The explanation of heredity most widely in favor during the 1800s was the blending hypothesis.  The hypothesis is the idea that genetic material contributed by the two parent mixes in a manner analogous.  Everyday observations and results of breeding experiments contradict that prediction also fails to explain other phenomena of inheritance such as traits reappearing after skipping a generation.  The Gene Idea: Parents pass on discrete heritable units- genes that retain their separate identities in offspring.

Mendel's Experimental Quantitative Approach  Around 1857 Mendel began breeding garden peas.  Mendel could strictly control mating between plants.  In nature flowers normally self fertilize.  Pollen grains from the stamens (pollen producing organs.) land on the carpel (egg bearing organ) of the same flower, and sperm released from the pollen grains fertilize eggs present in the carpel.  To achieve cross-pollination Mendel removed the immature stamens of a plant before pollen was produced and brushed them with pollen from another plant.

Mendel's Experimental Quantitative Approach Continued.  Mendel chose to track only those characters that varied between two distinct alternatives.  This meant that his plants had white or purple flowers.  Mendel also made sure that he started his experiments with varieties that over many generations of self-pollution had produced only the same variety as the parent plant.  This means if a plant with purple flowers is true breeding if the seeds produced will give rise to purple flowers.  Mendel usually followed traits for at least the P, F1, and F2 generations.  If he stopped at the F1 generations the basic patterns of inheritance would have escaped him.

Law of Segregation  Mendel's Law of Segregation applies to two (or more) alleles (alternative versions of a gene). The law says that alleles segregate (separate from each other) at some point before the formation of gametes, and are combined randomly at fertilization.

 This is figure 14.2 this  how Mendel did his  experiment by using  cross pollination.