| What it is: |
The tendency of two or more genes on the same chromosome to be inherited together. At the gene level, closeness ‘makes the heart grow fonder’ (so to speak). Anyway, the closer genes are on the same chromosome, the greater their chances of being inherited together and the less likely they are to be lost in the shuffle during crossing over. The physical closeness of the traits is important. So, the closer two genes are on the chromosome, the less likely that recombination (crossing over between two chromosomes) will occur. An example: If you want to know if someone will inherit bushy eyebrows, you can look for what is usually inherited with this trait in this family. If 6 thumbs are inherited 95% with bushy eyebrows and facial tics 60% of the time, what is more linked? Thumbs are.
Now, this is difficult because it is different than association. So, bushy eyebrows may be associated with facial tics, but that doesn’t mean they are linked. For example, bushy eyebrows may cause people to be nervous and they develop tics OR the tics make it impossible to pluck the bushy eyebrows. In general, associations go one way. Linkage can go either way in the general population, but within one family it they should be consistent. So, with the above example, having 6 thumbs may be linked to bushy eyebrows in one family but linked to normal eyebrows in the other. This is because different families can have different alleles encoded on that physical amount of DNA. |
