Notes Chapter 14 Mendel and the Gene Idea AP Biology 2 Notes Chapter 14 Mendel and the Gene Idea

Gregor Mendel Who was Mendel? Pure breeds 3 Generations 4 Hypotheses Mendel – Austrian Monk in 1850s Studied pea plant genetics working with flower color Pure Breeds always produce same trait when self pollinated ex:purple flowers 3 generations P(true breed parents) F1 and F2 4 hypothesis Mendel formed concerning genetics and passing of traits

Mendel’s 4 Hypothesis Alleles account for variation in inherited characteristics If the 2 alleles differ, dominant is expressed, recessive is hidden Ex: purple/white flower or round eyes/almond eyes 2 alleles segregate during meiosis For each character, you inherit 2 alleles Law of Segregation One from each parent Always 50/50 chance for a trait with different alleles

Law of Segregation

Useful Vocabulary Homozygous / Heterozygous Genotype / Phenotype

Punnett Squares Monohybrid crosses Dihybrid crosses Test Cross Pedigrees Test Cross used to determine genotype of organism w/ dominant phenotype cross with recessive organism and observe results Dihybrid Crosses BbEe x bbee Prove law of independent assortment: each allele is passed seperately in gametes (brown hair is not always associated with brown eyes) Pedigrees - family tree that can trace a particular trait or disease

Rules of Probability Genes are like coins Rules of Multiplication Bio 2 choices & not related to any other gene/coin Chance is always ½ Rules of Multiplication p both coins being heads? Bio chances of getting white flower from Pp self fertilization?

Rules of Probability

Exceptions to the 2 Allele Rule Incomplete Dominance Codominance Pleiotropy Epistasis Polygenic Inhertiance Incomplete - hybrids will have appearance inbetween Codominance -both alleles are expressed (blood types) dominant traits are not always the more populated. Ie. polydactyly – more than 5 fingers or toes 1/400 born with extra Pleiotrophy - gene has multiple effects on organism (sickle cell) Epistasis - 1 gene alters phenotypic expression of another gene mice coat color 1 trait = black/brown 2nd traint is color/no color (pigment deposted in hair) Polygenetic Inheritance traits controlled by more than 1 gene. Involve shades of variation (hair color, skin color, height) Norms 0f Reaction – range of phenotypes possible for a specific genotype, based on environmental factors skin color  suntain, weight  diet

Genetic Disorders Dominant genetic disorders Many not lethal as would not be able to passed on Huntington’s – late in life deteriorates nervous system (should you find out?) Recessive genetic disorders Cystic Fibrosis – must have aa to have it (no code for protein) (27 years) Tay Sachs – failure to break down brain lipid (3-5 years) Sickle Cell – Aa have fairly normal function Multifactorial Diseases Determined by more than 1 gene and environment Heart disease, cancer, diabetes, alcoholism

Genetic Tools and Counseling Genetic counseling Fetal testing Amniocentesis (Mid pregnancy)(14-16wks) Chorionic Villi Sampling (Earliest)(8-10wks) Ultrasound (Anytime) Fetoscopy Newborn screening (PKU)