Genetic linkage facts for kids
Genetic linkage happens when certain alleles (different forms of a gene) that are on the same chromosome tend to be passed down together during meiosis. This means they don't separate randomly, which is different from what Mendel's second law describes for genes on different chromosomes.
Imagine chromosomes as long strings of beads, where each bead is a gene. If two genes are on the same string, they usually stay together when that string is passed on. This is what we call genetic linkage.
What is Genetic Linkage?
Genes are linked when they are found on the same chromosome. Because they are on the same chromosome, they tend to be inherited together by the next generation. Genes on different chromosomes usually sort themselves out independently. This means they can mix and match in many ways when passed on.
How Genes Can Separate
Even if genes are on the same chromosome, they don't always stay together. During meiosis, which is how our bodies make special cells for reproduction, chromosomes can swap parts. This process is called crossing over. When crossing over happens, pieces of DNA are exchanged between chromosomes.
If two genes are far apart on a chromosome, there's a higher chance that a crossing-over event will happen between them. This can cause the genes to separate and go into different reproductive cells. If they are very close together, it's less likely they will be separated by crossing over.
Mapping Genes on Chromosomes
Scientists can use genetic linkage to figure out how far apart genes are on a chromosome. They look at the offspring of organisms that have two linked traits. They count how many offspring inherit the traits together and how many inherit them separately.
The more often the traits separate, the farther apart the genes are on the chromosome. This is because a greater distance means a higher chance of crossing over. This method was one of the first ways to create "maps" of genes on chromosomes.
The distance between genes is measured in "genetic map units" (m.u.) or "centimorgans." One centimorgan means that for every 100 times reproductive cells are made, the genes will separate once due to crossing over. By finding these distances for many genes, scientists can build a detailed map of a chromosome.
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