BIOL 206 (TEST 2) QUESTIONS AND CORRECT DETAILED
ANSWERS (VERIFIED ANSWERS) |ALREADY GRADED
A+||BRAND NEW
Population genetics of multiple loci Ans✓✓✓• During meiosis, the two
copies of a chromosome are pulled apart and packaged randomly into
gametes. There is 50% chance that a gamete receives the 'yellow' or
'blue' chromosome of each one. (independent assortment)
• Therefore, loci on different chromosomes have a 50% chance of being
packaged together in the same gamete.
• We call this state "linkage equilibrium"
• The probability of loci being swapped by recombination depends on
the distance between them.
• Loci far apart are less linked, loci close together are tightly linked.
Recombination Ans✓✓✓If loci are on exact opposite ends of the
chromosome then the loci often recombine - in this case all gamete types
are equally likely
If loci are so closely linked that recombination never occurs, and the
alleles at the two loci are inherited together
Genetic Linkage Ans✓✓✓refers to the linkage of multiple loci due to
the fact that they are transmitted through meiosis together
Linkage disequilibrium (D) Ans✓✓✓refers to the relationship between
the alleles at different loci; this may be due to physical genetic linkage
,but does not necessarily imply this (e.g. could be due to population
structure).
Two loci are said to be in linkage disequilibrium (D>0) when knowing
the allele at one locus enables you to predict what the allele at the other
locus likely is
What eliminates linkage disequilibrium from a population Ans✓✓✓•
Unless no other evolutionary process prevents it (e.g. selection) linkage
is broken down by recombination.
• Crossing over during meiosis breaks up old combinations of alleles and
creates new combinations.
• Unlike Hardy-Weinberg for a single locus, the process of breaking up
disequilibrium between two loci takes more than a single generation
Causes of Linkage Disequilibrium Ans✓✓✓• Physical Linkage of locus
A and locus B on same chromosome
• Natural selection favouring AB or ab combinations (vs. Ab or aB)
• Gene flow (population structure) AABB individuals newly arrive in
aabb populations
• Assortative mating AB and AB gametes mate; ab and ab gametes mate
How can we use Linkage Disequilibrium Ans✓✓✓1) Studying
migration or dispersal between populations with different gene
frequencies, or between species
2) Reconstructing the history of genes and populations
, 3) Identify alleles under selection
4) Mapping of genes underlying traits of interest (ie. use as a tool to
discover the causal genes or gene region)
Mapping of genes underlying traits Ans✓✓✓- the number of genomic
regions that influence a quantitative trait
- the magnitude of their effects
- their location in the genome
Then follow up on candidate genes to identify the causal loci and the
proteins they encode
Identifying loci under quantitative traits Ans✓✓✓Quantitative trait
locus (QTL) is a region of the genome that is correlated with variation in
a phenotypic trait. The region contains the genes (and other genes linked
to it) that contribute to population differences in a phenotype.
QTL analysis uses an experimental cross to create linkage
disequilibrium (because only one generation of recombination), and then
uses molecular markers throughout the genome to find the regions where
there is a statistical association between the phenotype of interest and the
molecular markers
Identifying loci under quantitative traits (cont.) Ans✓✓✓In populations
like humans we cannot do experimental crosses necessary for QTL
analysis. This has led to the development of other strategies (that are
now used in all sorts of organisms).
ANSWERS (VERIFIED ANSWERS) |ALREADY GRADED
A+||BRAND NEW
Population genetics of multiple loci Ans✓✓✓• During meiosis, the two
copies of a chromosome are pulled apart and packaged randomly into
gametes. There is 50% chance that a gamete receives the 'yellow' or
'blue' chromosome of each one. (independent assortment)
• Therefore, loci on different chromosomes have a 50% chance of being
packaged together in the same gamete.
• We call this state "linkage equilibrium"
• The probability of loci being swapped by recombination depends on
the distance between them.
• Loci far apart are less linked, loci close together are tightly linked.
Recombination Ans✓✓✓If loci are on exact opposite ends of the
chromosome then the loci often recombine - in this case all gamete types
are equally likely
If loci are so closely linked that recombination never occurs, and the
alleles at the two loci are inherited together
Genetic Linkage Ans✓✓✓refers to the linkage of multiple loci due to
the fact that they are transmitted through meiosis together
Linkage disequilibrium (D) Ans✓✓✓refers to the relationship between
the alleles at different loci; this may be due to physical genetic linkage
,but does not necessarily imply this (e.g. could be due to population
structure).
Two loci are said to be in linkage disequilibrium (D>0) when knowing
the allele at one locus enables you to predict what the allele at the other
locus likely is
What eliminates linkage disequilibrium from a population Ans✓✓✓•
Unless no other evolutionary process prevents it (e.g. selection) linkage
is broken down by recombination.
• Crossing over during meiosis breaks up old combinations of alleles and
creates new combinations.
• Unlike Hardy-Weinberg for a single locus, the process of breaking up
disequilibrium between two loci takes more than a single generation
Causes of Linkage Disequilibrium Ans✓✓✓• Physical Linkage of locus
A and locus B on same chromosome
• Natural selection favouring AB or ab combinations (vs. Ab or aB)
• Gene flow (population structure) AABB individuals newly arrive in
aabb populations
• Assortative mating AB and AB gametes mate; ab and ab gametes mate
How can we use Linkage Disequilibrium Ans✓✓✓1) Studying
migration or dispersal between populations with different gene
frequencies, or between species
2) Reconstructing the history of genes and populations
, 3) Identify alleles under selection
4) Mapping of genes underlying traits of interest (ie. use as a tool to
discover the causal genes or gene region)
Mapping of genes underlying traits Ans✓✓✓- the number of genomic
regions that influence a quantitative trait
- the magnitude of their effects
- their location in the genome
Then follow up on candidate genes to identify the causal loci and the
proteins they encode
Identifying loci under quantitative traits Ans✓✓✓Quantitative trait
locus (QTL) is a region of the genome that is correlated with variation in
a phenotypic trait. The region contains the genes (and other genes linked
to it) that contribute to population differences in a phenotype.
QTL analysis uses an experimental cross to create linkage
disequilibrium (because only one generation of recombination), and then
uses molecular markers throughout the genome to find the regions where
there is a statistical association between the phenotype of interest and the
molecular markers
Identifying loci under quantitative traits (cont.) Ans✓✓✓In populations
like humans we cannot do experimental crosses necessary for QTL
analysis. This has led to the development of other strategies (that are
now used in all sorts of organisms).
