Genetics

Over 12,000 years ago… 12,000 years ago people learned they could change animals by controlling how they reproduced.

The same happened with plants like wheat, rice, potatoes, corn, apples The same happened with plants like wheat, rice, potatoes, corn, apples . . . . Most plants that give us food today have been bred to be more useful.

But no one knew why or how it happened!

Finally, in the 1800’s an Austrian Monk discovered the secret!

Mendel worked in a monastery garden Mendel worked in a monastery garden. He wondered why pea plants had different traits…

Mendel experimented with thousands of pea plants Mendel experimented with thousands of pea plants. He crossed tall plants with tall plants, short with short, and tall with short traits. For example, Tall Pea Plants (TT) with Short Pea Plants (tt).

SO…Mendel’s cross between tall pea plants yielded all tall pea plants SO…Mendel’s cross between tall pea plants yielded all tall pea plants. His cross between small pea plants yielded all small pea plants. X = X = Mendel’s cross between tall pea plants and small pea plants yielded all tall pea plants. x =

Mendel then crossed these second generation tall pea plants and ended up with 1 out 4 being small. x =

Mendel’s Big Discovery Traits (such as plant height) are determined by individual, separate sets of information inherited from two parents, not by single sets of information. The two separate sets of information do not mix!

The information is carried on chromosomes.

Gene: Section of DNA on a chromosome, information that controls a characteristic. Allele: Different forms of a gene, determines a trait. Characteristics Traits Genes Alleles

3 Kinds of Alleles Dominant: An allele whose trait always shows up when the allele is present. Recessive: An allele that is hidden when a dominant allele is present. Co-dominance: Neither of two alleles is dominant or recessive, they both show up.

Combinations of Alleles Pure-bred: Two of the same alleles for a trait. Hybrid: Two different alleles for a trait.

Combinations of Alleles Homozygous: Having two identical alleles for a trait ** Pure-breds are homozygous Heterozygous: Having two different alleles for a trait ** Hybrids are heterozygous

Genotype and Phenotype Phenotype: An organism’s physical appearance, TRAITS YOU SEE. Ex. Brown Hair Genotype: An organism’s allele combinations, the GENETIC MAKE UP. Ex. BB Alleles are represented by letters. Uppercase letters are used for dominant Lowercase letters are used for recessive

Brown Hair [B]: dominant to all others Blond Hair [b]: dominant to red Red Hair [r]: recessive to all others Genotype BB Bb bb br rr Phenotype Brown Blond Red