Pierce Genetics A Conceptual Approach 3e：皮尔斯遗传学的概念：

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1、GENETICS ESSENTIALSConcepts and Connections SECOND EDITIONBenjamin A. Pierce 2013 W. H. Freeman and CompanyCHAPTER 5Linkage, Recombination, and Eukaryotic Gene MappingChapter 5 Outline 5.1 Linked Genes Do Not Assort Independently, 114 5.2 Linked Genes Segregate Together and Crossing Over Produces Re

2、combination Between Them, 116 5.3 A Three-Point Testcross Can Be Used To Map Three Linked Genes, 128 5.4 Genes Can Be Located with Genomewide Association Studies, 137The case of male baldness X-linked or not? Study of linkage of a SNP and the association with male pattern baldness shows that they do

3、 not assort independently, they are transmitted together5.1 Linked Genes Do Not Assort Independently Linked genes: genes located close together on the same chromosome-Belong to the same linkage groupRecombination and alleles Flower color and pollen shapeF1 generation gives purple color and long poll

4、enAppears that the purple is dominant to red and long is dominant to short pollenWhat with the F2, it is expected to get 9:3:3:1BUTThere is no 9:3:3:1 ratio; what happened5.2 Linked Genes Segregate Together and Crossing Over Produces Recombination Between Them Notation for crosses with linkage Compl

5、ete linkage leads to nonrecombinant Gametes and nonrecombinant progeny Crossing over with linked genes leads to recombinant gametes and recombinant progenyLabeling alleles of two genes on a same chromosome Cross AA BB x aa bb can be represented byA B a bA B x a bThe F1 will be:A Ba bAlso it can be r

6、epresentedA Ba bThe two test cross cases Linked . not linkedLinked genes give only nonrecombinant gametesUnlinked genes give both nonrecombinant and recombinant Concept Check 1For single crossovers, the frequency of recombinant gametes is half the frequency of crossing over because:a. a test cross b

7、etween a homozygote and heterozygote produces heterozygous and homozygous progeny.b. the frequency of recombination is always 50%.c. each crossover takes place between only two of the four chromatids of a homologous pair.d. crossovers take place in about 50% of meiosis.What happens in recombination

8、and the gamete formation5.2 Linked Genes Segregate Together and Crossing Over Produces Recombination Between Them Calculating Recombination Frequency Recombination frequency = (No. recombinant progeny/Total No. of progeny) 100% Coupling and Repulsion Configuration of Linked Genes Coupling (cis confi

9、guration): wild-type alleles are found on one chromosome; mutant alleles are found on the other chromosome.Calculating frequenciesCalculating frequenciesRec. Frequency = x100% Rec. Frequency = x100% 8 + 7 55+53+8+7# of recombinant progenyTotal # of progenyRec. Frequency = x100% 15123 5.2 Linked Gene

10、s Segregate Together and Crossing Over Produces Recombination Between Them Coupling and Repulsion Configuration of Linked Genes Repulsion (trans configuration): wild-type allele and mutant allele are found on the same chromosome. Testing for Independent Assortment Coupling and repulsionp+ b+p bp+ bp

11、 b+Coupling and repulsion Gene Mapping with Recombination Frequencies: Genetic maps are determined by recombinant frequency. Map unit and centiMorgans Constructing a Genetic Map with the Use of Two-Point Testcrosses5.2 Linked Genes Segregate Together and Crossing Over Produces Recombination Between