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Linked Genes: Definition & Examples

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  • 0:00 What Are Linked Genes?
  • 1:10 Gamete Packaging of…
  • 2:04 Gamete Packaging of…
  • 2:45 Recombination
  • 3:50 Examples of Linked Genes
  • 4:22 Lesson Summary
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Lesson Transcript
Instructor: Katie Chamberlain

Katie has a PhD in Microbiology and has experience preparing online education content in Biology and Earth Science.

Gene linkage is one of those things that can turn even the simplest genetic question into a complex mess. This lesson will teach you what a linked gene is and take you through some solid examples.

What Are Linked Genes?

Linked genes are genes that are found near each other on the same chromosome. The basic definition is very simple, but understanding how linkage impacts genetic inheritance will require a bit more information.

Genome Packaging

Every gene contains the recipe for making something that the body needs. Many genes connect together to form a long strand of DNA called a chromosome. Genes that are on the same chromosome are linked.

Being located on the same chromosome is special during meiosis when gametes (sperm and eggs) are formed because linked genes will usually be packaged together into a gamete.

Normal human cells have two copies of each chromosome, but gametes each only have one copy. This way, after fertilization, the new embryo will have the regular amount again. It will get half its chromosomes from the sperm and half from the egg.

Okay, so then how does the body decide which of the two versions of each chromosome to package into a gamete? Well, it is actually random! Each version has a 50/50 shot of getting included. The only rule is that the gamete must get one copy of each chromosome.

Gamete Packaging of Unlinked Genes

So, let's go through an imaginary situation where a gamete is being made. The person has two copies of chromosome 1, which contains the hair color gene. He has one copy with a brown allele and one copy with a red allele (alleles are different versions of a gene). He also has two copies of chromosome 2, which contains the freckle gene. One version has the freckle allele and one has the no-freckle allele.

As the gamete is being made it will get one version of each chromosome, and it doesn't matter which version as long as it gets a hair color gene and a freckle-status gene. It could end up with brown hair and freckles, brown hair and no freckles, red hair and freckles, or red hair and no freckles. Either hair color is just as likely to pair with each freckle status. Since hair and freckles are not linked, you are just as likely to have red hair and freckles as you are to have red hair and no freckles.

Gamete Packaging of Linked Genes

However, what if the freckle gene was also on chromosome 1? Now, the genes are linked. Let's say that one version of chromosome 1 has brown hair and no freckles and the other version has red hair and freckles. Now, when a gamete is made, brown hair and no freckles are stuck together traveling on the same chromosome. The red hair and freckles are also stuck together.

Since the traits are linked, a red hair containing gamete is no longer equally likely to have freckles or no freckles. If a gamete gets the gene for red hair, it usually gets the gene for freckles. Note: this is all just an example. In real life, the story of red hair and freckles is not this simple.

Recombination

In our example, the only way for red hair to end up in a gamete with no freckles is through recombination at the beginning of meiosis. This is a process where the two versions of a chromosome swap their DNA. They each get cut at the same spot, but instead of reattaching the same way, they reattach with the other chromosome.

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