biol139-lecture18-2011

biol139-lecture18-2011 - Linkage and recombination Linkage...

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Unformatted text preview: Linkage and recombination Linkage and recombination Chapter 5 Chapter 5 pp 123 - 135 pp 123 - 135 pp 143 - 151 igenetics pp 143 - 151 igenetics BIOL 139 BIOL 139 If genes on different chromosomes If genes on different chromosomes assort independently because of the assort independently because of the independent segregation of homologs independent segregation of homologs during meiosis, how do genes on the during meiosis, how do genes on the same chromosome assort ? same chromosome assort ? Genes on the same chromosome are said to exhibit linkage linkage called linked genes linked genes linked genes said to belong to a linkage group linkage group Some genes on the same chromosome assort Some genes on the same chromosome assort together more often than not together more often than not In dihybrid crosses, departures from a 1:1:1:1 ratio of In dihybrid crosses, departures from a 1:1:1:1 ratio of F F 1 1 gametes indicates that the two genes are on the gametes indicates that the two genes are on the same chromosome not completely independent of same chromosome not completely independent of each other each other In other words, they are in close proximity to one another and therefore tend to assort together = genetically linked genetically linked . Some genes on the same chromosome are more closely linked linked than others How can we tell this? How can we tell this? Morgans flies Morgans flies Remember: Remember: two genes on different chromosomes two genes on different chromosomes assort assort independently independently during meiosis during meiosis i.e. YYRR x yyrr = YyRr (F i.e. YYRR x yyrr = YyRr (F 1 1 ) = gametes: YR, Yr, yR and yr ) = gametes: YR, Yr, yR and yr parental parental recombinants 4 types of gametes should occur with a ratio of 1:1:1:1 50% parental, 50% recombinant when assort independently P P Parentals Parentals Progeny in which combination of alleles resemble parental phenotype Recombinants Progeny in which non-parental combination of alleles show in phenotype Linkage example of sex-linked (X) Linkage example of sex-linked (X) w+ = red eyes w = white eye y+ = brown body y = yellow body w y+ w y+ w y+- eggs Pure breeding Pure breeding Pure breeding Pure breeding White-eye/brown body White-eye/brown body Red-eye/yellow body Red-eye/yellow body w+ y w+y-sperm Red-eye/brown body Red-eye/brown body w+ y w y+ white-eye/brown body white-eye/brown body Brown is dominant to yellow Remember criss-cross inheritance Heterozygous female Notice: Notice: All females are red-eyed, brown body -heterozygous All females are red-eyed, brown body -heterozygous all males look like mother (inherited X) -white eyed, brown body all males look like mother (inherited X) -white eyed, brown body F1 female sets standards for dominance (red/brown) F1 female sets standards for dominance (red/brown) What will the F2 generation look like?...
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biol139-lecture18-2011 - Linkage and recombination Linkage...

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