EK Biology Book > Typos

[futuredoctor10]

EK: Gram-positive bacteria... "The space between the plasma membrane and the cell wall is called the periplasmic space" (p. 65)

Error: The periplasmic space is unique to gram negative organisms.

EK: "Genes located close together on a chromosome are more likely to cross over together, and are said to be linked" (p. 49)

Error: I am not sure but think this is wrong. Genes located further apart are more likely to undergo genetic recombination/crossing over.

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[Airplay355]

I think the second part means genes close together are more likely to cross over together, not more likely to have a cross between them. So the two genes would move together because of their close proximity.

 

[G1SG2]

EK: Gram-positive bacteria... "The space between the plasma membrane and the cell wall is called the periplasmic space" (p. 65)

Error: The periplasmic space is unique to gram negative organisms.

EK: "Genes located close together on a chromosome are more likely to cross over together, and are said to be linked" (p. 49)

Error: I am not sure but think this is wrong. Genes located further apart are more likely to undergo genetic recombination/crossing over.

You're correct.

 

[cyclin M]

EK: "Genes located close together on a chromosome are more likely to cross over together, and are said to be linked" (p. 49)

Error: I am not sure but think this is wrong. Genes located further apart are more likely to undergo genetic recombination/crossing over.

hmm I might be wrong, but I think this is not a typo and what EK has written is correct.

Genes closer together are linked because when crossing over occurs both are more likely to cross over together.

However what you said is true as well.

So what you said is basically like:

EK: the sky is blue
You: no, the sky is not red

Both are true. Just recognize that CROSSING OVER (recombination) and CROSSING OVER TOGETHER (linked) are not the same thing.

Here's a good explanation by someone else:

No, it is not a typo. Imagine that G represents a gene of interest, and any - represents genes on a chromosome we don't care about.

If our genes are positioned on the chromosome as shown, and two chromosomes crossover at X, then our genes near each other are likely to crossover together. In other words they are linked:

G-G---------
X
-------------

Now, if our genes our further apart and the crossover occurs at the same region of the chromosome:

G-------G---
X
------------

Each chromosome after the crossover will contain only one of the genes of interest. In other words, the genes did not crossover together. They are not linked.

If our genes started on two different chromosomes, they are more likely to recombine back onto the same chromosome when they are further apart on the chromosomes. In other words, the further apart two genes are on homologous chromosomes (shown below), the more likely they are to recombine.

--G--------------

--------------G--

will recombine more than


--G--------------
-----G-----------

 

[futuredoctor10]

Yeah the second statement is not a typo. I saw Toomuchresearch's diagrams in another thread after posting this, and they help clarify everything.

CROSSING OVER (recombination) and CROSSING OVER TOGETHER (linked) are not the same thing.

Yeah keeping this in mind helps- crossing over together (linked) on the same chromosome vs. crossing over 2 genes on diff chromosomes/recombination