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Unformatted text preview: BILD 3 Fall 2008 Section: Mon 9-9:50 AM HANDOUT 2 I. Workshop 3 parts: Mendelian genetics, Hardy-Weinberg, mitosis/meiosis o Mendelian genetics Definitions Gene DNA sequence that encodes for protein Alleles different versions/forms of a gene Locus location of gene on chromosome Gregor Mendel Worked with pea plants whose gene had only 2 alleles, one dominant and one recessive Experiment 1: monohybrid cross (one trait) Ratio of F2: ________ _ Experiment 2: dihybrid cross (two traits) Ratio of F2: ___________ Page 1 Homozygotes (PP, pp) / heterozygote (Pp) P ( dominant ) = purple, p ( recessive ) = white Each parent produces gametes that receives only one allele in parental generation, every gamete has same allele because parents are homozygous for each allele In F1 generation, half of gametes produced will have P allele and other half will have p allele During fertilization, each maternal gamete has same probability of combining with paternal gametes and therefore, Punnett square is used to visualize all possible genetic combinations/genotypes of offspring PRACTICE EXERCISE : As a refresher, draw a dihybrid cross of the color (yellow v. green) and shape (round v. wrinkled) traits through parental, F1, and F2 generations. Let A = yellow, a = green, B = round, b = wrinkled Write the ratio of the resulting F2 generation on the line inside the box. BILD 3 Fall 2008 Section: Mon 9-9:50 AM Mendels laws Law of segregation two alleles of a gene segregate (separate) during gamete formation Law of independent assortment each pair of alleles assorts independently of the other pair during gamete formation (seen in dihybrid crosses) Exceptions to Mendelian genetics Co-dominance of alleles: results in blending-like phenotypes in heterozygotes o Example: RR = red flower, Rr = pink flower, rr = white flower o Ratio of F2 generation no longer 3:1, it is ____________ Linkage between close genes: since genes are located on chromosomes, the closer they are, the higher the probability that they will be passed on together in one gamete (violates law of independent assortment) o Application to population : more closely-linked two genes are, more likely that when selection pulls one gene in one direction, it will indirectly pull the other in the same direction because these genes are linked o Hardy-Weinberg Law 2 parts Allelic frequencies will remain unchanged in absence of 4 factors o Mutation introduction of new allele Page 2 Draw example of gamete formation of heterozygote following law of independent assortment. BILD 3 Fall 2008...
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