Heredity : the passing of traits from parent to offspring Traits are controlled by genes Genetics: The study of how traits are inherited.

GREGOR MENDEL First known geneticist and “father of genetics” Did most of his genetic studies on pea plants performed cross-pollination, where he controlled which plants mixed.

WHAT ARE ALLELES? One form of a gene (there can be more than one form) Sex cells have one form of a gene on their chromosomes Body cells have two forms or alleles for a single gene (you got one from Mom and one from Dad) One may be dominant over another. If this happens, the dominant gene is the one expressed. If not, the recessive trait is expressed.

DOMINANT AND RECESSIVE A dominant trait will always be expressed and will hide a recessive trait A recessive trait can only be expressed if there are no dominant alleles present. Example: Brown eye color is dominant and blue is recessive. A person can have a brown allele and a blue allele but still have brown eyes because the brown allele is dominant and hides the blue allele.

Example: R= dominant r = recessive Generally, dominant alleles are represented with a capital letter, and recessive alleles are represented with a lower case letter. Each organism is represented by a PAIR of letters, one for each allele. Example: R= dominant r = recessive

Purebred species have two alleles of the same trait Represented by two of the same letters. This is called homozygous. For instance: BB or bb. Species with two different alleles or two different forms of the gene would be a hybrid Represented by two different letters and is called heterozygous. For instance: Bb

The PHYSICAL trait that shows, regardless of genotype is called a PHENOTYPE. For instance, Blue or Brown Eyes. The alleles present in the organism are referred to as its genotype. For instance, BB, Bb, or bb.

Steps for using the Punnett square: One parent’s alleles (genotype) go along the top The other parent’s alleles go down the side. You fill in the squares like doing the communicative property of multiplication. B b BB Bb B Bb bb b