Week 5 Terms 1600 s o Eukaryotic cell has a nucleus o Chromosomes are long strands of DNA and associated Proteins o A gene is a portion of DNA that codes for protein o Each gene can have several alleles or alternative forms o a pre made human was contained in every sperm cell many thought that an offspring s traits were blended from each parent o mother purple flowers o father white flowers o offspring light purple flowers Law of Inheritance o Mendel used the garden pea plant to study how traits were inherited Easy to grow Quick reproduction Cross pollinated by hand of the plant Had easily observable traits This allows the scientist control over the crossing mating o First Mendel examined traits that have two expressions like short and tall o Short and short always produced short offspring o When tall plants were crossed the results were variable Sometimes tall plants Sometimes short plants Sometimes short plants disappeared but then reappeared in future generations o The tall trait seemed to obscure the short trait o The tall trait was dominant to the short trait The allele for tall was dominant The allele for short was recessive Gene is plant height allele is short or tall o Dominant allele represented by capital letter o Recessive allele represented by lowercase letter T t o Some genes can have hundreds of alleles Law of Segregation look at 5 15 o During meiosis only one copy of each gene is placed in each gamete o A diploid cell can only have two alleles gene o If those 2 alleles are the same the individual is homozygous TT or tt o If those 2 alleles are different the individual is heterozygous Tt Laws of Inheritance o Genotypes express the genetic makeup of an individual Homozygous dominant TT Homozygous recessive tt Heterozygous Tt o Phenotypes are the outward expression of the individual The outward expression of the gene Tall or short o Mendel developed a system to keep track of all his crosses matings Parental generation P generation P s offspring F1 generation F1 s offspring F2 generation And so on Law of Inheritance o Started with a P generation that was TT or tt o Crossed TT with tt F1 generation was all tall o Next he took plants from the F1 generation and set up a monohybrid cross gene Mating between 2 individuals that are heterozygous for one trait F2 for every 3 tall plants there was 1 short plant Phenotypic ratio 3 tall 1 short o Punnett square uses the genotypes of the parents to reveal which alleles the offspring might inherit All three possible genotypes are possible in the F2 generation Genotypic ratio 1 TT 2 Tt 1 tt o In a monohybrid cross both parents are heterozygous Tt for height Exceptions to Mendel s Laws Mendel s prediction o There are some situations in which phenotypic ratios do not conform to o Example Incomplete Dominance occurs when a heterozygote has an intermediate phenotype between the 2 homozygotes o Homozygous red flower crossed with a homozygous white flower results in all pink flowers Incomplete Dominance o 2 pink flowers crossed results in 1 white 1 red and 2 pink o Red and white flowers return in the F2 generation o The single copy of the R allele in the heterzygote codes for less pigment production than 2 copies of the R allele do Polygenic Traits o Polygenic traits depend on more than one gene Most inherited traits are polygenic The phenotype reflects the activity Ex eye color is encoded by multiple genes Sex linked Traits o Males are XY o Females are XX o Sex linked traits are carried on the X chromosome o To be color blind a male must inherit it from his mom parent but a woman needs to inherit from both parents Patterns of inheritance differ for men and women o Male must inherit normal color vision from his mother but a female can inherit from either parent Environmental Effects o Skin color is a polygenic trait that is influenced by the environment Week 6 Viewpoint before Darwin o The earth was young 6 000 years old o Each species was created at the same time and doesn t change or die out o The number of species never changes o Advances in science led to awareness of change in lines of descent of o 18th and 19th century naturalists tried to reconcile traditional beliefs with species evidence of change Evolution o The genetic change in a population over time Genetic change is a change in allele frequency Population group of individuals of the same species that are interacting same place same time o Darwin s observations on a voyage around the world in 1831 led to new ideas about species Resemblance of extinct and living species Modern armadillo vs extinct glyptdont Variations in traits influence an individual s ability to secure resources o Influence survival and reproduction Darwin Wallace and Natural Selection o 1858 Wallace sent Darwin his ideas on evolution by natural selection o Both presented at a conference o Darwin published On the Origin of Species in 1859 sold out on the first day Theory of Natural Selection o Natural selection Different survival and reproduction among individuals of a population whose traits vary Mechanism of evolution Heritable traits that allow for greater reproductive success become more common in a population over time Fitness is a measure of relative reproductive success 3 Conditions for Natural Selection o 1 Variation for a trait o 2 Variation must be heritable Able to be passed down coded for in your genes o 3 Differential Reproductive Success More offspring are produced than can survive Creates competition for resources Some are better competitors and they are able to survive and reproduce Survival of the Fittest is not of physical strength Evolution by Natural Selection o The result of natural selection is a population that is well adapted to its current local environment o Not a perfect organism o In each generation the alleles that code for traits with better fitness tend to increase in frequency o If the environment changes which alleles are favored may also change o Galapagos Finches In dry years the finches had to eat large hard seeds and bigger beaks were selected for In wet years finches could eat small soft seeds and smaller beaks were selected for o When the environment changes Traits that were once helpful may be harmful Other traits which have little value may become adaptations Three Modes of Natural Selection o Natural selection may favor the Intermediate phenotype Stabilizing selection One extreme phenotype Directional selection Both extremes in phenotype o Stabilizing selection