Genetics Analysis & Principles Exam 2 Chap 6,7,8 latest version |well
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When is a chi square analysis is applied to solve a linkage problem, explain why an independent
assortment hypothesis is proposed.
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?
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.
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.
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, What is the difference in meaning between the terms genetic recombination and crossing over?
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?
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?
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.
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.
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