Fundamentals of Genetics Bio preAP/GT

Patterns of Inheritance The History of Genetics Genetics - scientific study of heredity Trait - characteristic that can be passed from parents to offspring Bio preAP/GT

Once accepted hypothesis Blending of Traits Once accepted hypothesis did not explain appearance of unexpected traits in offspring Oops…blond baby boy. Where did that come from? Bio preAP/GT

Gregor Mendel - 1860’s self-fertilization - cross of the same plant; offspring receives genetic information from one parent only cross-fertilization - cross of 2 different plants; offspring receives different forms of genetic trait from each parent Studied pea plants Bio preAP/GT

Hybrid - organism receives different forms of a genetic trait Purebred - organism receives the same genetic traits from both of its parents Hybrid - organism receives different forms of a genetic trait Bio preAP/GT

Mendel’s Observations Crossed two different purebreds (P generation = parent generation) resulting offspring is F1 (1st filial) -offspring Bio preAP/GT

crossed these, resulting in F2 (2nd filial) generation Found that there were always two types of traits - Dominant and Recessive Bio preAP/GT

Mendel’s Conclusions: Disproved blending hypothesis offspring receives one of two “factors” from each parent - “factors” are genes genes - sections of a chromosome that code for a trait Bio preAP/GT

Allele - distinct form of a gene Bio preAP/GT

dominant allele - expressed when two different alleles are present; represented with a capital letter: A recessive allele - form of a gene that is not expressed when paired with a dominant allele; represented with a lower case letter: a Bio preAP/GT

Mendel is the Father of Modern Genetics Gregor Mendel Bio preAP/GT

Cellular Basis of Inheritance Chromosome Theory of Heredity states that the material of inheritance is carried by the genes in the chromosomes Bio preAP/GT

Genes represent traits Genotype - genes that make up an organism includes both genes in a homologous pair Phenotype - outward expression of the trait Bio preAP/GT

homozygous - two alleles are identical (AA or aa) also known as purebred organism heterozygous - two alleles are different (Aa) also known as a hybrid organism Bio preAP/GT

Mendel’s Laws Law of Segregation - gene pairs separate when gametes form one gamete carries one gene and the other carries the other gene Bio preAP/GT

Law of Independent Assortment - gene pairs segregate into gametes randomly and independently of each other Bio preAP/GT

Law of Dominance - dominant allele is expressed, recessive allele will be hidden unless in homozygous form Bio preAP/GT

Genetics and Prediction Bio preAP/GT

Predictions for One Trait Probability - predict likelihood of an event or outcome “tails” “heads” “Heads” is one possible outcome out of a total of 2 possible outcomes. Bio preAP/GT

Punnett square - grid for organizing genetic information can be used to make predictions about a cross between two organisms monohybrid cross - cross between two parents involving one trait P p Bio preAP/GT

AA x aa (A = normal, a = albino) Bio preAP/GT

Genotypic ratio = AA 0/4 or 0% Aa 4/4 or 100% aa 0/4 or 0% Phenotypic ratio = Normal 4/4 or 100% Albino 0/4 or 0% Bio preAP/GT

Predictions for Two Traits Two trait cross – cross between two parents and two traits Dihybrid cross - cross between two heterozygous parents use a 4 X 4 punnett square sixteen possible outcomes Bio preAP/GT

HhTt x hhtt (H = long hair, h = short hair; T = tail, t = no tail) FOIL! Ht hT ht HT ht HhTt Hhtt hhTt hhtt Hhtt hhTt hhtt ht HhTt ht HhTt Hhtt hhTt hhtt ht HhTt Hhtt hhTt hhtt Bio preAP/GT

Genotypic ratio = HHTT 0/16 or 0% HHTt 0/16 or 0% HHtt 0/16 or 0% HhTt 4/16 or ¼ or 25% Hhtt 4/16 or ¼ or 25% hhTT 0/16 or 0% hhTt 4/16 or ¼ or 25% hhtt 4/16 or ¼ or 25% Bio preAP/GT

Phenotypic ratio: 25% Long hair, tail 25% Long hair, no tail 25% short hair, tail 25% short hair, no tail JK! Bio preAP/GT

Test Cross G? GG or Gg Test cross - breed an organism whose genotype is questionable with a homozygous recessive organism results determine genotype of questionable organism then it’s Gg If all offspring gg X G? then it’s probably GG If any offspring Bio preAP/GT

Incomplete Dominance color in snapdragons, hypercholestolemia, instead of white or red – color is pink heterozygous offspring show a phenotype that is in-between the phenotypes of the two homozygous parents blending of traits X Bio preAP/GT

r w r rr rw w rw ww Bio preAP/GT

Codominance HA = normal HS = sickle Both alleles are expressed equally both are dominant and equally expressed – both normal red blood cells and sickle-shaped blood cells present in heterozygote Both alleles are expressed equally Ex. Sickle Cell Disease Bio preAP/GT

Polygenic Trait (Epistasis) Trait controlled by more than one gene ex. Eye color Bio preAP/GT

Multiple Alleles Three or more alleles for a trait in a human population ex. Blood types: IA, IB, i (type O) Karl Landsteiner discovered antigens which are responsible for different blood types Bio preAP/GT

Multiple Alleles - Blood Types IA - contains antigen A IB - contains antigen B IAIB - contains antigens for both A & B i - contains neither A nor B Bio preAP/GT

Blood Groups Bio preAP/GT

Universal recipient: AB Dominant Trait in Blood Groups Universal donor: O Universal recipient: AB Dominant Trait in Blood Groups Rh antigen = named after Rhesus Monkey people who have the Rh antigen = Rh+ (positive) people who do not have it = Rh- (negative) Rh-, Rh+ person = positive Bio preAP/GT

Pleiotropy Single gene affects more than one trait ex. Sickle cell anemia - effects include blood cell shape, anemia, weakness, brain damage, spleen damage, & heart damage Bio preAP/GT

Environmental Effects Phenotype is a combination of genetic and environmental influences, epigenetics Ex. Identical twins share the same DNA but may look and act differently ex. Himalayan rabbit - fur color depends on body temperature – dark where cooler, white where warmer Yes, they are identical! Bio preAP/GT

Issues in Biology Up to a 3 inch height difference observed in studies where twins were raised in two different countries/environments “Nature vs. Nurture” Issue studies have been done on identical twins that have been separated at birth VS Twins raised in different adoptive homes showed similar interests and careers when they reconnected as adults Bio preAP/GT