Gregor Mendel Experimented with pea plants and discovered some patterns of inheritance Genetic Inheritance = passing genetic information from one generation to the next Mendel (1822-1884)

Traits, Genes and Alleles Trait = an inherited characteristic of a living thing Examples: height and color Gene = a piece of DNA that codes for a protein Example: Gene for purple color in flower petals Allele = different version of a gene (different DNA sequence) Example: Allele for purple protein and white protein

Mendel’s Crosses

Mendel’s Crosses Mendel created plants that were pure-bred Pure-bred plants are plants that have the same traits generation after generation He mated, or crossed, 2 different pure-bred plants to produce hybrids A hybrid is an organism that has two different types of DNA, usually 2 diff. alleles

Mendel’s Crosses What do you expect in the next generation?

Mendel’s Principle of Dominance For some genes, alleles can be dominant or recessive Dominant alleles prevent recessive alleles from being seen (Symbol = Capital Letter) Recessive alleles are only seen when they are the only copies of the gene (Symbol = Lowercase Letter)

Mendel’s Question: Why did the white flower trait disappear in the F1 generation and re-appear in the F2 generation? What do you expect in the next generation?

Mendel’s Explanation Each organism has two versions of every gene (2 alleles) 1 allele is received from each parent

Mendel’s Explanation Gametes are reproductive cells like sperm and eggs

Mendel’s Explanation When a parent creates gametes, the two alleles segregate, or separate, and enter different gametes Mendel named this idea the Law of Segregation

Mendel’s Explanation When two hybrids are crossed, ¼ of the offspring will inherit two copies of the recessive allele

Questions How does the prediction of 3:1 compare to Mendel’s experimental data? Why might there be some differences?