05-Linkage-1 - Non-Mendelian Genetics segregation of linked...

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Non-Mendelian Genetics segregation of linked alleles crossing over linkage in Drosophila two-point mapping in Drosophila three-point mapping in maize interference
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Gamete formation when two heterozygous gene pairs are on different chromosomes: Mendel’s independent assortment Two metaphase 1 tetrads Four different types of gametes AaBb
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Gamete formation when two heterozygous gene pairs are on the same chromosomes but no exchange of chromosomal segments occurs between them: linkage All gametes produced are noncrossover ( parental , P) One metaphase 1 tetrad Two types of gametes
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Crossing over Crossing over is the exchange of chromosomal material between homologous chromosomes by breakage and reunion . occurs during prophase I of meiosis ( pachytene ) Result : parental gametes are still produced, but some non parental ( recombinant ) gametes are generated at a lower frequency
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Gamete formation when two heterozygous gene pairs are on the same chromosomes and exchange of chromosomal segments occurs: linkage and recombination Gametes produced: noncrossover ( parental , P) and crossover ( non parental , NP) Four different types of gametes
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Single crossover event between two nonsister chromatids outside the area of the two genes: no recombination of alleles only parental gametes are produced result : two types of gametes
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parental and recombinant gametes are produced result : four types of gametes; parentals in higher proportion hypothetical limit for recombinant percentage: 50% Single crossover event between two nonsister chromatids in between the two genes: recombination of alleles
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brown locus: bw + : red eye ( dominant ) bw : brown eye ( recessive mutant ) heavy wing vein locus: hv + : thin wing vein ( dominant ) hv : heavy wing vein ( recessive mutant ) Alleles in two autosomal Drosophila loci P 1 cross bwbw hv + hv + X bw + bw + hvhv
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F 1 gametes Complete linkage no recombination occurs •F 1 individuals can only produce parental gametes ( theoretical )
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F 1 cross: bw + bw hv + hv X bw + bw hv + hv a non-Mendelian dihybrid cross
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Complete linkage Notice : in the P 1 generation, the parents were both homzygous dominant for one character and homozygous recessive for the other character •as a result, all the F 1 individuals were heterozygous for both
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This note was uploaded on 11/13/2009 for the course PCB 3063 taught by Professor Sotero during the Fall '09 term at University of Central Florida.

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05-Linkage-1 - Non-Mendelian Genetics segregation of linked...

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