Why does having a extra or one less chromosome have such an impact on the body
In: 4
Bio refresher: you have 23 pairs of chromosomes numbered in decreasing size except the last two which are the sex chromosomes XY or XX. Each chromosome is a wrapped up strand of DNA encoding genes.
If you’re baking a cake but add half as much of some ingredients or too much of some ingredients there will be problems with the final cake.
Gene regulation is tightly regulated, but it is set up for 2 of each chromosome (with the exception of sex chromosomes which are a bit more complex). If you have one more or one less chromosome the genes on them will be expressed in the wrong amounts which can be catastrophic.
In fact it’s often lethal which is why most cases of an extra chromosome happen with the smallest chromosomes. An extra copy of chromosome 21 (smallest somatic chromosome) causes down syndrome, an extra copy of the larger 13 or 18 are lethal within the first year of life, most other trisomy’s would result in miscarriages. Missing a whole chromosome is almost always lethal. The exception is turner syndrome (a woman missing one X) which is only survivable because women mostly “turn off” one of their x chromosomes. It’s not fully off which is why turner syndrome has symptoms but it’s close enough that its not lethal.
Latest Answers