©1999 Timothy G. Standish Who was Gregor Mendel? Father of classical genetics In 1856, Mendel started growing and studying peas. He demonstrated how the traits of the pea plant behaved in a precise mathematical way (probability).

©1999 Timothy G. Standish Why did Mendel use peas? True-breeds were available. They are easy to grow. They have many easy to observe traits including: –Seed color - Green or yellow –Seed shape - Round or wrinkled –Pod color - Green or yellow –Pod shape - Smooth or constricted –Flower color - White or purple –Flower position - Axial or terminal –Plant size - Tall or dwarf

©1999 Timothy G. Standish What were Mendel’s experiments? Go to

©1999 Timothy G. Standish How did Mendel interpret his results? CC Cc cc In the F 1 generation, the white allele was hidden by the purple “dominant” allele In the F 2 generation, 1/4 of the offspring wound up with two copies of the white allele thus they were white Cc C c F 2 Generation Cc CC c c F 1 Generation Gametes from the P generation Heterozygous parents make gametes either one or the other allele The F1 Generation is all heterozygous Homozygous parents can only make gametes with one type of allele

©1999 Timothy G. Standish What is the Principle of Independent Assortment? When Mendel crossed peas and looked at two different traits, he discovered that the traits assorted independently In other words, if he was looking at the height of the plants and the color of the flowers, all four possible combinations of height and flower color were produced: Tall Purple Tall white dwarf Purple dwarf white

©1999 Timothy G. Standish TcTc tCtC tctc TCTCt ct ct Ct CT cT cT CT C Independent Assortment TtCcTtCcTtCCTTCcTTCC TtccTtCcTtCcTTccTTCc ttCcttCCTtCcTtCcTtCC ttccttCcTtccTtCcTtCc As long as genes are on different chromosomes, they will assort independently

©1999 Timothy G. Standish What is the Principle of Segregation? The two alleles for a parent separate during the formation of gametes (sex cells) so that each gamete carries only one allele for each trait. This occurs during Meiosis.