Biology 2050 Lect Mendel and Genetics Monohybrid Crosses and part of Dihybrid Crosses Mendel was an Augustinian Monk in which experimented with pea plants of various traits and is credited with becoming the founder of modern science of genetics Character a heritable feature in which varies among individuals in a species Example Flower Color and Height in pea plants Trait a variant for a specific trait found within the individuals Example purple vs white flowers tall vs short plants True breeding the term used to describe a specific individual within Mendel s studies it was considered true breeding if the individual s offspring were identical to itself in the instance of self pollination Hybridization the breeding or crossing of two true breeding parents The different generations within the study were The P Generation Parental Generation true breeding parents The F1 Generation the hybrid offspring of the true breeding parents The F2 Generation the offspring produced after the F1 generation self pollinate or pollinate with others of their generation Mendel s Model consists of four related concepts which are Alternative versions of genes account for variations in inherited characteristics Alleles the alternating forms or versions of a gene For each character an organism inherits two copies of a gene on from each parent When two parents are crossed the offspring have traits from both individuals Example Pea plant 1 is true breeding in purple another is bred with it Parent 1 that is true bred for white Parent 2 p p P Pp Pp P Pp Pp PP Purple plant pp white plant As it is seen the offspring get both alleles though the offspring are Purple If the two alleles at a locus differ then one the dominant allele determines the organism s appearance The other recessive allele has no noticeable effect on the organism s appearance Example In Mendel s experiment the purple trait was the most promenade trait and was dominate over the white flowers Dominate Allele the trait that is visibly seen in the individual Recessive Allele the trait that is not as promenade as dominate however can be seen within individuals within a population in which contain two of these traits As seen in the trait chart above Law of segregation Independent Assortment the two alleles for a heritable character segregate during gamete formation meiosis and separate Punnett Square the chart seen above in which can show possible offspring trait combinations Homozygous an organism that has a pair of identical alleles Heterozygous an organism that has two different alleles present for a gene Test Cross a cross with two dominate individuals one dominate dominate and the other dominate recessive Example Fur Color in rabbits Brown B white b B B b Bb Bb b Bb Bb The individuals within this example are a brown individual BB and a white individual bb As seen in the Punnett square the offspring have both traits but brown is the visible one Depending on what the individual s gametes are will determine the traits of the offspring Phenotype the trait that is observable Example Purple vs White Genotype the genetic makeup of the organism Example Pp PP pp Monohybrid heterozygous for one particular trait When these individuals cross with only trait Dihybrid a cross between two hybrids with two traits Monohybrid has been the cross that has been used thus far An example of a dihybrid cross is as follows A tall purple flower PpTT is crossed with a short white flower pptt PT PT pT pT pt pt pt pt PpTt PpTt ppTt ppTt PpTt PpTt ppTt ppTt PpTt PpTt ppTt ppTt PpTt PpTt ppTt ppTt Independent assortment example Tall T Purple P Short t White p Chromosomes Meiosis 1 T T As it can be seen the multiple traits are a bit confusing but together they many form a tall purple individual or tall white one P P Need to Memorize Meiosis 2 The Most often used phenotypic ratios monohybrid 3 1 dihybrid 9 3 3 1 Most often used genotypic ratios monohybrid 1 2 1 dihybrid 1 2 2 4 1 2 1 2 1