1 Chapter 10: Mendel’s Laws of Heredity What is Heredity? Heredity The passing on of characteristics from parents to offspring through genes Genes A section on DNA that carries the information on what type of protein to make; they influence the types of traits an organism inherits Traits Characteristics that are inherited Genetics The branch of biology that studies heredity History of Genetics Gregor Mendel: an Austrian monk that first developed the study of genetics Experimented with pea plants to discover the general laws of genetics A pea plant has gametes and both male and female reproductive organs o Gametes: male and female sex cells o Pollination: transfer of pollen (male gametes) from a male reproductive organ to a female reproductive organ in a plant Mendel allowed pollination to occur within the same flower or between different flowers for his experiments Fertilization: the male gamete unites with the female gamete to form a zygote (a fertilized cell) o In the case of pea plants, the zygote becomes a seed Conducted crosses between pea plants to compare traits o Monohybrid crosses: when only one trait is compared at a time (like eye color) o Dihybrid cross: when two traits are compared at a time (like eye & hair color) P1 = Parental generation (parents) F1 = First filial generation (children) F2 = Second filial generation (grandchildren) Mendel’s Conclusions 1. The rule of unit factors * Each organism has two factors, or genes, that control each trait o One gene comes from mom, one gene comes from dad A single gene can exist in different forms called alleles o Example: Blue, brown, and green are alleles for the eye color gene 2 2. The rule of dominance * Offspring inherit an allele from each parent, but only one trait is observed Dominant trait: “stronger” trait that shows up when the dominant allele is present o Represented by a capital letter; B is for brown eyes Recessive trait: “weaker” trait that shows up only when the dominant allele is not present o Represented by a lowercase letter; b is for blue eyes The Law of Segregation What is means: Every organism has 2 alleles of each gene When gametes are made, each gamete receives only one of these alleles During fertilization, the offspring will receive one allele for each gene from each parent Ex. If the trait for height is represented by the allele “T” = tall and “t” = short, Parents: Tt x Tt Punnett Squares Shorthand way of determining the probability of having a certain type of offspring if you know the parents’ genotypes Phenotypes & Genotypes Phenotype: the physical appearance of an organism o Ex. Brown eyes Genotype: genetic makeup of an organism o Ex. Alleles for eye color are Bb or BB (= brown eyes) Homozygous: 2 alleles for a trait are the same o BB is homozygous dominant for brown eyes o bb is homozygous recessive for blue eyes o Homozygous offspring are called purebred because their alleles are the same Heterozygous: 2 alleles for a trait are not the same o Bb is heterozygous o Heterozygous offspring are called hybrids because their alleles are mixed Mendel’s law of independent assortment Genes for different traits are inherited independently of each other 3 Example: You have brown hair (Bb) and freckles (Ff) o You can pass on to your children one of the following combinations: B + F, b + F, b+f B + f,