Mendel and the Gene Exam 3 Bio 1107 Genetics is the branch of biology that focuses on inheritance Heredity is the transmission of traits from parents to their offspring A trait is any characteristic of an individual Hypotheses that tried to explain why offspring resemble parents and how transmission of traits occurred o Blending inheritance Parental traits blend such that their offspring have intermediate traits o Inheritance of acquired characteristics Parental traits are modified and passed on to their offspring Garden Peas First Model Organism in Genetics o Model organism is a species used because it is practical and can draw conclusion from them that can be applied to other species o Easy to grow short reproductive cycle large number of seeds matings are easy to control traits are easily recognized o Peas usually self fertilize pollinate themselves Prevented self pollination by removing male reproductive organs containing pollen o Mendel worked with pure lines individual that produce offspring is identical to self Used theses plants to create hybrids whose offspring is from mating two pure lines that differed in one or more traits Mendel s Experiment w Single Trait o The adults in the cross were the parental generation Progeny offspring are the F1 generation First filial o Round is dominant and F1 was all round Contradicted blending o F1 then self pollinated Wrinkled seed trait reappeared in F2 o Monohybrid cross is mating between parents with two different genetic determinant for a trait o Did gender influence inheritance He performed a reciprocal cross a cross in which the phenotypes of the male and female are reversed compared with a prior cross Showed same results genetic determinant location does not matter o Mendel proposed a hypothesis called particulate inheritance which suggests that hereditary determinants maintain their integrity from generation to generation Contradicts blending and inheritance of acquired characteristics hypothesis o A gene is a hereditary determinant Each individual has two version of each gene called alleles Alleles found called genotype o Principle of Segregation Two members of each gene pair must segregate into different gamete cells eggs and sperm o Mendel s genetic model Is a set of hypotheses that explain how a particular trait is inherited and explains results of theses crosses o A Punnett Square is used to predict genotype and phenotype Mendel s Experiment with Two Traits o Mendel used a dihybrid cross Cross between two pure lines that differ in two observed traits Principle of segregation o Principle of Independent Assortment one another o Using a testcross to confirm predictions Alleles of different genes are transmitted independently of A testcross is a parent with homozygous recessive for a particular trait is mated with parents that has the dominant phenotype but unknown genotype Independent assortment Chromosome Theory of inheritance o States that chromosomes are composed of Mendel s hereditary determinants and physically separate the alleles during anaphase of meiosis I responsible for Mendel s principle of segregation o Genes for different traits assort independently of one another at meiosis I because they are located on different nonhomologous chromosomes and assort independently Testing Chromosome Theory o Fruit flies used wild type most common type of phenotype for each trait red eye Mutations are phenotype different with wild type resulting from a change in genes o Mated wild type female with mutant male All had red eye o Did reciprocal cross relationship between sex of progeny and eye color Discovery of Sex Chromosomes o Females have 20 large male have 19 large y small o Sex linked inheritance Chromosome theory of inheritance was correct Extending Mendel s Rules o Rediscovered because researched began to analyze traits an alleles who inheritance was more complicated o Linkage is the tendency of particular alleles of different genes to be found on same chromosome Predicted to always be transmitted together during gamete formation and should violate principle of independent assortment To see if linked genes behave as predicted Morgan performed experiment using drosophilia Both heterozygous for two sex linked traits o Flies refereed to as recombinant Gametes with new recombinant genotypes were generated when crossing over occurred during prophase of meiosis I in females Linked genes are inherited together unless crossing over o Genetic Map is the diagram showing relative position of a gene on occurs chromosome Frequency of crossing over it used to create genetic map Percentage of recombinant offspring can be used to estimate location of gene relative to one another on the same chromosome o More likely to cross over when genes are far apart Multiple alleles and Polymorphic traits o Multiple allelism is when genes have more than two alleles o When more than two distinct phenotypes are present in a population due to multiple allelism the trait is polymorphic o I gene controls production of polysaccharide attached to glycoprotein Incomplete Dominance and Codominance o Incomplete dominance occurs when the heterozygotes have an intermediate phenotype 4 o clocks o A heterozygous organism that displays the phenotype of both alleles of a single gene is said to display codominance Blood Pleiotropy o Some genes can influence many traits said to be pleiotropic Marfan Syndrome Increased height limb length potentially severe heart problems Physical environment also affects phenotype o Phenotype often as much a product of environment as genotype o Phenylketonuria PKU Phenylalanine accumulates in body and results in profound Interactions with other genes Affect Phenotype mental retardation o Expression of many genes depends on the presence or absence of other genes Quantitative Traits o Mendel worked with discrete traits traits that are clearly different from one another Seed color is yellow or green No intermediate o Traits that are not discrete but fall into a continuum are called quantitative traits Height Many genes each contribute a small amount to the value of Population frequency is bell shaped curve showing normal a quantitative traits distribution o Transmission of quantitative traits results from polygenic inheritance where each gene adds a small amount to the vale of the phenotype Wheat color Applying Mendel s rules to humans o Pedigree Genetic relationships among individuals sex phenotype Dominant or recessive and sex or