What would have happened if genes had been absent on the selectively permeable
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Less chromosome means missing some genetic material, which if it contains meaningful content, will likely result in one or more (1) missing enzymes, or (2) insufficient enzyme production (assuming that the companion chromosome without the deletion is expressing *some* of the enzyme). The effect could be minor, but likely seriously debilitating or lethal. Most genetic deletions cause fetal death very early in pregnancy.
More chromosome means added genetic material or duplicated genetic material. If expressed, this means extra enzymes (or proteins). If the enzyme is over-expressed, this causes two things, (1) the depletion of its substrate, and (2) the increase of its reaction product. In trisomy 21 (Down's syndrome), the over-expression of SOD-1 (superoxide dismutase, coded on the 21st chromosome) decreases superoxide levels and increases hydrogen peroxide levels. SOD's job is to convert superoxide into hydrogen peroxide, and it does it roughly 50% faster in individuals with Down's syndrome than in those without.
Also in Down's syndrome, two of the seven collagen genes are on the 21st chromosome, which causes a mis-allocation of collagen resources into two types of collagen protein and corresponding depletion of five other types of collagen protein. This causes joint laxity (extreme joint mobility/flexibility).
Some (many?) "normal" people experiencing genetic stress (chemo, drug therapies, methylation deficiencies, etc.) have trisomy-21 cells circulating in their blood streams (and presumably in their tissues, too.). But these trisomy-21 cells do not yet appear to have any direct negative consequence. But the genetic stress does cause other genetic consequences that can be very serious.
If the extra genetic material is an entire chromosome, the effect is largely lethal. Few chromosomes have sufficiently few genes that they can be over-expressed without catastrophic consequences.
More chromosome means added genetic material or duplicated genetic material. If expressed, this means extra enzymes (or proteins). If the enzyme is over-expressed, this causes two things, (1) the depletion of its substrate, and (2) the increase of its reaction product. In trisomy 21 (Down's syndrome), the over-expression of SOD-1 (superoxide dismutase, coded on the 21st chromosome) decreases superoxide levels and increases hydrogen peroxide levels. SOD's job is to convert superoxide into hydrogen peroxide, and it does it roughly 50% faster in individuals with Down's syndrome than in those without.
Also in Down's syndrome, two of the seven collagen genes are on the 21st chromosome, which causes a mis-allocation of collagen resources into two types of collagen protein and corresponding depletion of five other types of collagen protein. This causes joint laxity (extreme joint mobility/flexibility).
Some (many?) "normal" people experiencing genetic stress (chemo, drug therapies, methylation deficiencies, etc.) have trisomy-21 cells circulating in their blood streams (and presumably in their tissues, too.). But these trisomy-21 cells do not yet appear to have any direct negative consequence. But the genetic stress does cause other genetic consequences that can be very serious.
If the extra genetic material is an entire chromosome, the effect is largely lethal. Few chromosomes have sufficiently few genes that they can be over-expressed without catastrophic consequences.
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