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Outcomes - Mendelian Inheritance1.characterisitics of Mendel's work that set him apart as a genetic researcherMendel’s methods illustrate how rigorous scientific work is conducted: through observation, making hypotheses, and testing the hypotheses with experiments.Most important innovation was his quantitative approach to science, specifically his rigour and statistical analysis.Knew nothing about mutation, meiosis, cells/nucleiCame up with fundamental model of inheritanceCareful experimentation with controlled crosses and quantitative analyses2.components of Mendel's explanatory modelVariation in traits due to different alleles/variation in genotypeFirst hypothesis was that the adult plants carry a pair of factors that govern the inheritance of each characterSecond hypothesis stated that if an- individual’s pair of genes consists of different alleles, one allele is dominant over the other, recessive, alleleThird hypothesis Principle of Segregation: Mendel’s principle that the pairs of alleles that control a character segregate as gametes are formed, with half the gametes carryingone allele and the other half carrying the other allele.
1.The genes that govern genetic characters are present in two copies in individuals.2.If different alleles are present in an individual’s pair of genes, one allele is dominant over the other.3.The two alleles of a gene segregate and enter gametes singly.Alleles separate randomly into gametesEach organism inherits 2 allelesPhenotype of heterozygote determined by dominant allele3.distribution of progeny, given parental genotypes in monohybrid and sex-linked crossesMonohybrid cross: cross that involves a single characterPunnet squarePP x pp: 100% Pp (genotype)•Phenotype: 100% dominant phenotypePp x Pp: 25% PP + 50% Pp +25% pp (genotype)•Phenotype: 75% dominant phenotype + 25% recessive phenotypeCan calculate number of offspring with each phenotype/genotype
Dihybrid cross:involving two characters9:3:3:1 Ratio
Sex Linked Genes (Reciprocal cross):inherited differently in males and females.In Mendel’s pea-plants it didn’t matter which parent had which trait, it matters in sex linked traitsSex linked traits are not carried on the Y chromosomes
4.parental genotypes, given distribution of progeny in monohybrid and sex-linked crossesFor a cross of Rr x Yy x Rr x Yy , when the gametes fuse randomly, the progeny will show a phenotypic ratio of 9:3:3:1. 5.location of various alleles on homologuesAlleles are located at the same spots on the homologous chromosomes, but they are DIFFERENTA locus, the site occupied by a gene on a pair of homologous chromosomes
Two alleles, A and a, of the gene are present at this locus in the homologous pair. These alleles have differences in the DNA sequence of the geneDifferent alleles located at same locus/spot on homologous chromosomes