genetics 5 - Genetics 5 Life 10.4 Chapter 5: Chromosome...

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Genetics 5 Life 10.4 Chapter 5: Chromosome Mapping in Eukaryotes -interlocus distance: degree of crossing over between any two loci on a single chromosome is proportional to the distance between them. Thus, depending on which loci are being considered, the percentage of recombinant gametes varies. -chromosome maps: correlation of loci and recombinant gametes creates this, indicating the relative locations of genes on the chromosomes I. Genes linked on the same chromosome segregate together -independent assortment: two genes on two different homologous pairs of chromosomes assort independently. No exchange -linkage without crossing over: two genes on a single pair of homologs. No exchange -linkage with crossover: two genes on a single pair of homologs. Exchange occurs between two nonsister chromatids. -complete linkage: no crossover so gametes are same as parents. Gametes produced in equal proportions -recombinant or crossover gametes: exchange generating two new allele combinations, involving only two nonsister chromatids of the four chromatids present. Other two chromatids are noncrossover -frequency of crossing over occurring between two linked genes is proportional to the distance separating the respective loci along the chromosome. As the distance between two genes increases, the proportion of recombinant gametes increases and that of parental gametes decreases. The limit of recombinant gametes approaches 50%. A. The linkage ratio -linkage ratio: created from when complete linkage exists between two genes because of their close proximity and organisms heterozygous at both loci are mated, creating a unique F2 phenotypic ratio. -represent linked genes by placing gene on one homolog above line and the other below line. P1: (bw hv+)/(bw hv+) X (Bw+ hv)/(bw+ hv). Since P1 is homozygous, F1 are all heterozygous and when F1 interbred, it only produces parental gametes. F2 generation have a 1:2:1 phenotypic and genotypic ratio. So 1 brown: 2 wild: 1 heavy. This is complete linkage between progeny is small. -linkage group: since genes located on same chromosome show linkage to one another, get this, which number of these correspond to the haploid number of chromosomes. II. Crossing over serves as the basis of determining the distance between genes during Chromosome mapping Crosses involving two genes demonstrating complete linkage will almost always produce a percentage of offspring resulting from recombinant gametes A. Morgan and Crossing Over -chiasmata: synapsed homologous chromosomes in meiosis wrapped around each other. Evident of points of overlap. Genetic exchange. Morgan concluded that if linked genes exist in a linear order along the chromosome, then a variable amount of exchange occurs between any two genes. -crossing over: closer two genes are less likely it is that a genetic exchange will occur.
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This note was uploaded on 09/20/2008 for the course BIO 315H taught by Professor Payne during the Spring '08 term at University of Texas at Austin.

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genetics 5 - Genetics 5 Life 10.4 Chapter 5: Chromosome...

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