Mendelian Genetics

How Genetics Began Gregor Mendel Father of genetics Austrian monk & plant breeder In 1866, published findings on the method of inherence in garden pea plants. Genetics: The science of heredity. Heredity: The passing of traits of the next generation.

Mendel studied pea plants Pea plants consistently produce off-spring with only one form a trait. Pea plants reproduce by self-fertilization. Mendel noticed that some pea plants always produced green seeds, while others always produced yellow seeds.

Mendel performed cross-pollination by transferring male gametes from the flower of a green-seed plant to the female organ of a flower from a yellow- seed plant. He called the green-seed plant & the yellow seed plant the parent generation, also known as the P generation.

The Results The resulting offspring had yellow seeds. The offspring from this first cross are called the first filial generation (F1). Mendel wanted to know: is the green-seed trait gone, or is it just hidden? Allowed the plants to grow & self-fertilize. This generation of seeds is called the second filial generation. (F2)

Results 3:1 Ratio of yellow to green seeds.

Mendel’s Conclusions 2 forms of the seed trait in the pea plants (yellow-seed & green-seed). Each form is controlled by a factor called an allele. Allele: An alternative form of a single gene passed from generation to generation. The gene for yellow seeds & the gene for green seeds are different forms of a single gene.

Vocabulary Dominant: Form of the trait that appeared. (Yellow-seeds in the F1 generation). Represented by a capital letter. (A) Recessive: Form of the trait that was masked. (Green-seeds in the F1 generation). Represented by a lower case letter. (a)

Vocabulary An organism that has 2 of the same alleles for a particular trait is homozygous for that trait. (AA or aa) An organism that has 2 different alleles for a particular trait is heterozygous for that trait.(Aa). The dominant allele is observed.

Vocabulary Genotype: The organism’s pair of alleles. (AA, Aa, aa) Phenotype: The observable characteristics of an allele pair. AA = Yellow-seed Aa= Yellow- seed aa = Green-seed