Why don't Linked genes follow Mendel genetics laws?

[thestrokes14]

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I am a bit confused about why linked genes aren't inherited in the expected way that unlinked genes are. Can someone clarify why there is a difference?

 

[LaurenMCAT]

I am a bit confused about why linked genes aren't inherited in the expected way that unlinked genes are. Can someone clarify why there is a difference?

Simply: they do NOT sort independently. 👍

The second law of Mendelian genetics discusses "independent assortment," which is typically how we think of genes behaving: flower petal color, plant height, pea size, etc.

Linked genes are "stuck together" like your sleeve is to your shirt:

Let's say you're getting dressed in the morning for class and it's REALLY early, you're really tired and you do NOT want to turn on the light. 😴

So...in the dark you grab a pair of pants from your pants drawer, a shirt from your shirt drawer, and socks from your socks drawer.

We'd say that these pieces of clothing are independent of one another. What pair of pants you grab has nothing to do with your shirt or your socks. They're in different drawers.

Now...what about the sleeves that you chose for your shirt?

That's ridiculous! They're STUCK to your shirt, right? Well theoretically they are, but if we really wanted to, we could detach them. But we won't. So we say that your sleeves and your shirt are linked. REALLY closely linked. What you choose for your shirt is essentially what you'd choose for your sleeves. They do not sort independently. Though they are not one and the same, they "segregate" together during cell division and are typically found together.

Does that make any sense!?!

 

[thestrokes14]

Simply: they do NOT sort independently. 👍

The second law of Mendelian genetics discusses "independent assortment," which is typically how we think of genes behaving: flower petal color, plant height, pea size, etc.

Linked genes are "stuck together" like your sleeve is to your shirt:

Let's say you're getting dressed in the morning for class and it's REALLY early, you're really tired and you do NOT want to turn on the light. 😴

So...in the dark you grab a pair of pants from your pants drawer, a shirt from your shirt drawer, and socks from your socks drawer.

We'd say that these pieces of clothing are independent of one another. What pair of pants you grab has nothing to do with your shirt or your socks. They're in different drawers.

Now...what about the sleeves that you chose for your shirt?

That's ridiculous! They're STUCK to your shirt, right? Well theoretically they are, but if we really wanted to, we could detach them. But we won't. So we say that your sleeves and your shirt are linked. REALLY closely linked. What you choose for your shirt is essentially what you'd choose for your sleeves. They do not sort independently. Though they are not one and the same, they "segregate" together during cell division and are typically found together.

Does that make any sense!?!

Yes, thank you! So, if we were to do a dihybrid cross for two particular genes, would there be less possible different gametes formed if the genes were linked, and thus the prototypic ratios would not be in the expected Mendel ratios?

 

[Rabolisk]

Yes, thank you! So, if we were to do a dihybrid cross for two particular genes, would there be less possible different gametes formed if the genes were linked, and thus the prototypic ratios would not be in the expected Mendel ratios?

Yes, and this is one way of measuring "how far" genes are located relative to each other.

 

[LaurenMCAT]

AWESOME!! You got it!