http://www.whitehouse.gov/omb/budget/fy2005/images/hud-2.jpg

The study of how traits are passed from parents to offspring.

http://history.nih.gov/exhibits/nirenberg/images/photos/01_mendel_pu.jpg

•Before anyone knew anything about DNA, Gregor Mendel began to study patterns of inheritance in plants.•His discoveries became the foundation for the field of genetics.•So what did he do? 1822-1884

http://fig.cox.miami.edu/~cmallery/150/mendel/c14x1sweetpeas.jpg

Let’s give one example…He crossed purple and white-flowered pea plants (P1 generation)

What do you suppose the offspring were like?

http://fig.cox.miami.edu/~cmallery/150/mendel/cross.htm

100% purple flowers

(F1)Then, he crossed

these purple offspring

What do you suppose the second generation of offspring (F2) were like?

75% purple 25% white

WHY?

To understand the results, we should review some vocabulary…

Gene: a part of a chromosome (DNA) that codes for one trait or protein.

http://www.gsi.de/forschung/bio/fig3.JPG

•Humans have 20-25,000 genes and 46 chromosomes•For each trait, we receive one gene from Mom and one from Dad

Genotype: a description of the genes using letters.

Dominant: a gene that always shows up in the phenotype. (capital letter)Recessive: a gene that is hidden by a dominant gene; shows up only when the dominant gene is not available. (lower case letter)

http://discover.edventures.com/images/termlib/g/genotype/support.gif

What are the genotypes and phenotypes for these flowers?

Phenotype: a physical description of the observed traits

Homozygous: two of the same letters in the genotype.

Heterozygous: two different letters in the genotype.