Review

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Review

• Mendelian genes are NOT linked and follow rules
  of simple dominance
• Linked genes
• Meiosis tetrads and chromatid segregation
• Crossing over/recombination
• Clarify recombination frequency
• 20, 50

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Crossing-Over
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Perspective Historically, the conclusions of
genetic experiments were based on the results of
selected matings In other words, we didnt know
what was happening inside the cell, but we could
make conclusions based on the phenotypic results
(e.g. ratios) of the offspring. It was only
recently that scientists were able to physically
illustrate what happens during many of these
complicated events, such as crossovers
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Perspective These lectures are based on the
relationship between genes within a cell, within
an individual, and within a population. When we
throw terms out there like Mendelian or
recombinant or nonparental or independent
(segregation), we are not making statements
about all of the genes, but rather about one gene
relative to another or one gene relative to a
few others
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If we were to pick 1 gene at random, it might
have 2 alleles that act in a manner of simple
dominance if we were to then pick another gene
at random, it might be on a separate chromosome,
which means it segregates independently of Gene
1 and if the trait associated with Gene 2 also
exhibited simple dominance, then we would have
picked two genes that fall under the description
of Mendelian genetics
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If instead, our Gene 2 was located on the same
chromosome, we would now refer to the
relationship between the 2 genes as linked,
which is non-Mendelian. If we couldnt actually
see the 2 genes to know they were linked, we
could find out by conducting several matings and
counting the number of offspring with each
possible phenotype.
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