Remember yesterday…??Unifying Ideas in Science:1) Cell theory – all organisms are made of cells and that all cells come from preexisting cells2) Evolution: species are related to one another and can changethrough time…it occurs by natural selection3) Evidence for change through time: A) fossil records, B) extinctions, C) transitional Forms, D) environmental/geological changea) planet changes, environment changes, species changeb) evidence of change: vestigal traits; contemporary examples (antibiotic resistance)E) species RelatednessHomologies (similarities) are inherited from a common ancestorDarwin’s postulates:1. Traits in a population vary among individuals2. Some traits are passed on to offspring (i.e. traits have a genetic basis and are heritable)3. Some individuals produce more offspring than others4. The subset of individuals that produce the most offspring is not a random sample of the population. Individuals with certain traits are more likely to produce the greatest number of offspring in a given environment. The individuals with these traits are “naturally selected”So. . . the population’s characteristics change as a result of natural selection acting on individualsTerminologyPopulation: group of the same species living in the same area at the same time Fitness: ability of an individual to survive and reproduce• Measured in units of # of offspring• High fitness = many offspringAdaptation: is a heritable trait that increases the fitness of an individual in a particular environment relative to individuals lacking the trait.Darwin at the Olympics• Work with your group to modify the 100-meter dash such that it would become an example of natural selection.Darwin’s postulates (hypotheses)1. Traits in a population vary among individualsThat is where Darwin got stuck . . . • But, where did that variation comefrom?• How is it propagated from onegeneration to the next?• He could demonstrate that traits areheritable, but not how.Mendel to the Rescue!The mechanism that explains the processGregor Mendel• 1822-1884• Monk; St. Thomas Abbey;pea plants• Involved in AgriculturalSociety*– Animal & Plant breeders knewthat traits could be inherited– Mendel sought to describethese patterns ofinheritanceMendel’s wise choice• Model organism(peas)• Statistical analysis oflarge sample size• Experiments spannedmultiple generations• Test crossesMendel’s advantages• Easy and inexpensive to keep and propagate• Short generation time• Prolific• Small (lots in small space)• Tolerant of inbreeding• Interesting and simple phenotypic variation• Small genome• Matings (experiments) were COMPLETELY within his controlEasy to pollinate• Self• Cross• Generate truebreedinglines(individuals that produce offspring identical to themselves when self pollinated or crossed with individuals in same population)Simple, informative traitsWhat did Mendel DO?• Created truebreeding lines* for various traits– homozygous• Crossed those pure wrinkles with pure rounds– Genotype*– Phenotype*(Gametes are produced via meiosis)All round? Hey, what is going on?• The wrinkled phenotype “receded”– Recessive (r)• round phenotype “dominated”– Dominant (R) Possible explanations?Gender dominance???Reciprocal cross“Mendel then planted the F1 seeds and allowed the individuals to self-pollinate when they matured.”(work with the person next to you)Draw a Punnett square of the cross.What kind of cross is this?What did the F2 generation look like (phenotype)?Why?Hey, what is with that 3:1 ratio?Mendel reasoned that each person has two versions of the same gene: alleleThe alleles that are found in a particular individual are called its genotypeTo explain the 3:1 ratio of phenotypes in F2 individuals, he reasoned that the two alleles of each gene must segregate(separate into different gamete cells during the formation of the egg and sperm in the parents)Principle of Segregation!Mendel then crossed the F1 offspring.(work with the person next to you)Draw a Punnett square of the cross .What kind of cross is this?What did the F2 offspring look like (phenotypes)?Why?Hypothesis:The 2 traits are independent• Dihybrid cross• These were Mendel’s results!• 9:3:3:1Law of independent assortmentWhat about that probability stuff?(work with the person next to you to translate this)a) If the mother and father are heterozygous for pea shape, what is the probability that you will get a homozygous dominant offspring?b) What is the probability of getting a heterozygote?Terminology• Phenotype, genotype• Diploid, haploid, gamete• Homologs/homologous• gene• Locus/loci• Allele• Homozygous, heterozygous• True-breeding, Hybrid, monohybrid cross• P, F1, F2 generation• Reciprocal cross• Dominant/recessive Partial (incomplete) dominance• Particulate inheritance (not blending)• Segregation of alleles• Independent assortment of