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Genetics problems - linkage and crossing over

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2. An individual with Turner's syndrome and afflicted with the X-linked recessive trait
nystagmus is produced by parents that are both phenotypically normal. The individual has a brother that is also afflicted with nystagmus and a brother that is phenotypically normal. Is it the paternal or maternal X that is missing in the Turner's syndrome female? How do you know?

9. P1 transduction was done to determine the order of the fadD, gap, and pabB genes relative to each other. The donor was fadD-gap+ pabB- and the recipient was fadD+ gap- pabB+. Gap+ transductants were selected. The coinheritance of the nonselected markers are shown in the table below.

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2. An individual with Turner's syndrome and afflicted with the X-linked recessive trait
nystagmus is produced by parents that are both phenotypically normal. The individual has a brother that is also afflicted with nystagmus and a brother that is phenotypically normal. Is it the paternal or maternal X that is missing in the Turner's syndrome female? How do you know? (4 points)

Answer - The boys got their X chromosome from their mother (they have to have gotten Y from father in order to be males). Nystagmus is an X-linked ...

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Genetics problems relating to linkage, map distance etc.

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Genetics--map units

Hi. Here's the problem:

In Zebrafish, 3 genes have been mapped on the third chromosome, in the order

fiz--6 m.u.---myob----14 m.u.-------sufi

The wild-type allele of each gene is dominant.

A strain that is
fiz myob sufi/+++
is testcrossed, and there are 1000 offspring fish.

1. How many fiz + + offspring would you expect to see in these 1000 offspring?

2. How many + + sufi offspring would you expect to see in these 1000 offspring?

I got two other questions regarding this problem correct: that there would be 400 wild-type offspring (a parental class) and only 4 "+ myob +" offspring (a double crossover class). But I can't seem to figure these two out.

My approach: If there are 6 map units between fiz and myob, then there's a 6% chance of a crossover between them. That is, a 6% chance of getting either "fiz + +" or "+ myob sufi". 6% x 1000 = 60. And the "fiz + +" class should be approximately half of that, which is 30.

But that's the wrong answer, and I'm not sure why.

Same thing with question number 2.

There are 14 m.u.'s between myob and sufi, so there's a 14% chance of a crossover between them, a crossover that would result in either "fiz myob +" or "+ + sufi." 14% x 1000 = 140. 140/2 = 70.

But again, that's not the right answer.

Can you explain to me how to do this problem, and the correct answers?

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