BIOB 375 1st Edition Lecture 18 Outline of Last Lecture I. Variations from Chromosome Reassortment IIa. Predicting variationsOutline of Current Lecture II. Variations that arise from chromosome recombinationa. Cross-overb. Coupling vs. RepulsionCurrent LectureVariations arise from chromosome recombinationConcept of linkage and recombination- Linkage refers to the genes located on the same DNA molecule or the same chromosome- Liked genes do not assort independently Recombination- Cross-over between two non-sister chromatids of the homologous chrmosomes- Cross-over can happen anywhere between two non-sister chromatidsCrossing-over is always happening during meiosis, but may not always happen between A and B lociWithout crossing over, only parental genotype (nonrecombinant) gametes are produced. With crossing over, two addition recombinant gametes are produced. Total the parental ones are more than the non-parental ones.Concepts of coupling and repulsion- When two gene loci are linked, the configuration of both dominant alleles of the two locion the same dnA strand, or both recessive alleles on the same strand is referred as coupling- When two gene loci are linked, the configuration of one dominant and one recessive allele of the two loci on the same DNA strand is referred to as repulsionWhy recombination increase variation?Practice on two types of Problems:Type 11. From given genotypes to predict genotypes of gametes formed2. From parent’s genotypes to predict offspring’s genotypesType 21. From given phenotypes and segregation ratios of the offspring to deduce the genotypes of the plantsNote: Most plants can use the pollens from an anther to pollinate a stigma of the same plant, this is called self-pollination or self. Self = P1 and P2 have the same genotypeWhen the A allele is completely dominant, the phenotypes conferred by AA and Aa are the same, and it’s often referred to as A_.- Phenotypes and ratios would be represented as ¾ A_, ¼ aaType
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