Genetics Analysis & Principles Exam 2
Chap 6,7,8 exam with complete solutions
When is a chi square analysis is applied to solve a linkage problem, explain why an
independent assortment hypothesis is proposed. - ANSWER-An independent
assortment hypothesis is proposed because it enables us to calculate the expected
values based on mendel's ratios. Using the observed and expected values, we can
calculate whether or not the deviations between the observed and expected values are
too large to occur as a matter of chance. if the deviations are very large, we reject the
hypothesis of independent assortment.
In your own words, explain why a testcross cannot produce more than 50%
recombinant offspring. When a testcross does produce 50% recombinant offspring,
what do these results mean? - ANSWER-A testcross cannot produce more than 50%
recombinant offspring because the pattern of multiple crossovers can only yield a
maximum of 50% recombinant.
When a testcross yields 50% recombinants, that means either1.) the two genes are on
two different chromosomes OR2.) the two genes are at least 50 m.u. apart
If you try to throw a basketball into a basket, the likelihood of succeeding depends on
the size of the basket. It is more likely that you will get the ball into the basket if the
basket is bigger. In your own words, explain how this analogy also applies to the idea
that the likelihood of crossing over is greater when two genes are far apart than when
they are close together. - ANSWER-The likelihood of scoring a basket would be greater
if the basket was larger. Similarly, the chances of a crossover initiating in a region
between two genes is proportional to the size of the region between the two genes.
There are a finite number (usually a few) of crossovers that occur between homologous
chromosomes during meiosis, and the likelihood that a crossover will occur in a region
between two genes depends on how big that region is.
, What is the difference in meaning between the terms genetic recombination and
crossing over? - ANSWER-Genetic recombination is the new combination of alleles in
the offspring.
Crossing over is the physical event when homologous chromosomes exchange pieces
and causes recombination to occur.
Explain why the percentage of recombinant offspring in a testcross is a more accurate
measure of map distance when two genes are close together. When two genes are far
apart, is the percentage of recombinant offspring an underestimate or overestimate of
the actual map distance? - ANSWER-When two genes are close together, the
percentage of recombinant offspring in a testcross more accurately measures map
distance because the closer together two genes are the less likely it is that double
crossovers occur between them.
The inability to detect double crossovers cause the map distance to be
underestimated.When two genes are far apart the percentage of recombinant offspring
is an underestimate of the actual map distance because the further apart two genes are
the more likely it is that double crossovers occur between them.
If two genes are more than 50 mu apart, how would you ever be able to show
experimentally that they are located on the same chromosome? - ANSWER-By
mapping a third gene that is in-between genes A and B you would be able to show they
are located on the same chromosome.
In Morgan's trihybrid testcross of Figure 7.3, he realized that crossing over was more
frequent between the eye color and wing length genes than between the body color and
eye color genes. Explain how he determined this. - ANSWER-He determined this by
observing gene pairs. He observed there were fewer number of recombinants between
the genes for body color and eye color and more recombinants between genes for eye
color and wing length.The greater the distance between two genes the greater the
number of crossovers and therefore recombinants.
How would you determine that genes in mammals are located on the Y chromosome
linkage group? Is it possible to conduct crosses (let's say in mice) to map the distances
between genes along the Y chromosome? Explain. - ANSWER-To determine if genes in
mammals are located on the Y chromosome linkage group you must observe if the
Chap 6,7,8 exam with complete solutions
When is a chi square analysis is applied to solve a linkage problem, explain why an
independent assortment hypothesis is proposed. - ANSWER-An independent
assortment hypothesis is proposed because it enables us to calculate the expected
values based on mendel's ratios. Using the observed and expected values, we can
calculate whether or not the deviations between the observed and expected values are
too large to occur as a matter of chance. if the deviations are very large, we reject the
hypothesis of independent assortment.
In your own words, explain why a testcross cannot produce more than 50%
recombinant offspring. When a testcross does produce 50% recombinant offspring,
what do these results mean? - ANSWER-A testcross cannot produce more than 50%
recombinant offspring because the pattern of multiple crossovers can only yield a
maximum of 50% recombinant.
When a testcross yields 50% recombinants, that means either1.) the two genes are on
two different chromosomes OR2.) the two genes are at least 50 m.u. apart
If you try to throw a basketball into a basket, the likelihood of succeeding depends on
the size of the basket. It is more likely that you will get the ball into the basket if the
basket is bigger. In your own words, explain how this analogy also applies to the idea
that the likelihood of crossing over is greater when two genes are far apart than when
they are close together. - ANSWER-The likelihood of scoring a basket would be greater
if the basket was larger. Similarly, the chances of a crossover initiating in a region
between two genes is proportional to the size of the region between the two genes.
There are a finite number (usually a few) of crossovers that occur between homologous
chromosomes during meiosis, and the likelihood that a crossover will occur in a region
between two genes depends on how big that region is.
, What is the difference in meaning between the terms genetic recombination and
crossing over? - ANSWER-Genetic recombination is the new combination of alleles in
the offspring.
Crossing over is the physical event when homologous chromosomes exchange pieces
and causes recombination to occur.
Explain why the percentage of recombinant offspring in a testcross is a more accurate
measure of map distance when two genes are close together. When two genes are far
apart, is the percentage of recombinant offspring an underestimate or overestimate of
the actual map distance? - ANSWER-When two genes are close together, the
percentage of recombinant offspring in a testcross more accurately measures map
distance because the closer together two genes are the less likely it is that double
crossovers occur between them.
The inability to detect double crossovers cause the map distance to be
underestimated.When two genes are far apart the percentage of recombinant offspring
is an underestimate of the actual map distance because the further apart two genes are
the more likely it is that double crossovers occur between them.
If two genes are more than 50 mu apart, how would you ever be able to show
experimentally that they are located on the same chromosome? - ANSWER-By
mapping a third gene that is in-between genes A and B you would be able to show they
are located on the same chromosome.
In Morgan's trihybrid testcross of Figure 7.3, he realized that crossing over was more
frequent between the eye color and wing length genes than between the body color and
eye color genes. Explain how he determined this. - ANSWER-He determined this by
observing gene pairs. He observed there were fewer number of recombinants between
the genes for body color and eye color and more recombinants between genes for eye
color and wing length.The greater the distance between two genes the greater the
number of crossovers and therefore recombinants.
How would you determine that genes in mammals are located on the Y chromosome
linkage group? Is it possible to conduct crosses (let's say in mice) to map the distances
between genes along the Y chromosome? Explain. - ANSWER-To determine if genes in
mammals are located on the Y chromosome linkage group you must observe if the
