Heredity and Punnett Squares

Gregor Mendel “Father of genetics” Genetics = study of patterns of inheritance Monk who described patterns of inheritance.

Mendel’s Peas

Genes, Traits Gene = segment of DNA that codes for a specific trait. Traits = characteristics that are inherited Ex: eye color, leaf shape

Dominant vs. Recessive Dominant = Form of a gene that is always expressed, represented by an uppercase letter (T). Recessive = form of a gene that is hidden when the dominant gene is present. Represented by a lowercase letter (t). Ex: TT or Tt will show dominant trait. Only tt will show recessive trait.

Allele Different form of a gene. Ex: hair color (black, brown, blonde, red, etc.) Homozygous (purebred) = two alleles that are the same. (ex: TT or tt) Heterozygous (hybrid) = two different alleles (ex: Tt)

Genotype and Phenotype Genotype: the genetic makeup of an organism (ex: BB, Bb, or bb). Phenotype: the physical expression of a trait (ex: eye color).

Segregation: chromosomes separate Law of Segregation Genes separate during gamete formation. Segregation: chromosomes separate

Law of independent assortment chromosomes separate independently of each other during meiosis

Generations Cross = mating of two organisms P = parental generation F1 = First filial generation (offspring) F2 = second filial generation (offspring from cross of F1) Filia = Latin for daughter

Probability Likelihood that something will happen. Predicts an average number of occurrences, not an exact number of occurrences. Probability = # of ways an event can occur # of total possible outcomes

Punnett Squares Used to predict the possible outcomes of a cross Expressed as ratios, fractions, or percentages. Axes represent the gametes of each parent. Boxes show the possible genotypes of the offspring.

Monohybrid cross involves one trait.