Ch. 5 - Linkage and Gene Mapping Flashcards
Give a brief important description of Thomas Hunt Morgan (1866 - 1945).
nobel prize winnter 1933
pioneered use of drosophila melanogaster in genetic studies by searching for mutants (took 2 years to find 1st one)
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Figure: (a) independent assortment: two genes on two different homologous pairs of chromosomes.
See figure in notebook and describe what is going on.
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Figure: (b) linkage: two genes on a single pair of homologs; no exchange occurs.
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Figure: (c) linkage: two genes on a single pair of homologs; exchange occurs between two nonsister chromatids.
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What is complete linkage?
no crossing over between two genes
produces parental (non-crossover) gametes
When does crossing over occur?
occurs between two nonsister chromatids
both parental and recombinant (crossover) gametes are produced
What is linkage ratio?
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What is linkage group?
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What is map unit (mu)?
1 percent recombination between two genes on chromosome
also called centimorgans (cM)
relative distances, not exact ones
Describe the process of a single crossover (SCO).
SCO is used to determine distance between two linked genes.
Describe the process of a double crossover (DCO).
will be a rare event
What is point crosses for mapping genes on a chromosome.
Ex: 1 point crosses, 2 point crosses, 3 point crosses.
How do you determine gene order?
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How do you determine recombination frequency?
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What is interference?
in inhibition of further crossover events
refers to the inhibition of crossovers by another crossover event nearby
reduces expected number of multiple crossovers
How do you calculate interference?
using coefficient of coincidence (C)
C is used to quantify disparities that result from interference
C = observed DCO é expected DCO
interference:
I = 1 - C
Interference: when is it complete?
when no double crossovers occur
Interference: when is it positive?
fewer double-crossover events than expected occur é is a positive number
Interference: when is negative?
more double-crossover events than expected occur é is a negative number
What occurs when genes are close together?
positive interference occurs
accuracy of mapping is high (mostly SCOs occur)
What happens to interference and accuracy of mapping when distance between genes increases?
interference decreases.
accuracy of mapping decreases because multiple crossover events (some of them undetectable at the phenotypic level) are occurring.
