genetics/cell bio- basic question but i'm still perplexed!

[puffylover]

i think i've confused myself with a practice question but can someone explain to me:

let's say a condition/disease is recessive. because both genes are defective, no protein is made and something goes wrong physiologically. (correct?)

if a person is heterozygous for a gene, does that mean that one chromosome produces the protein and so everything is alright?? or something else happens?

so writing this out confused me even more ....

when you have a double helix, the double helix represents one chromosome, right? like, the chromosome you inherited from your dad (forgetting crossing over).

so in a diploid cell you have all 46 + sex chromosomes being transcribed and translated?

wahh i dunno why i'm getting confused over such a simple topic. i feel like genetics (macro) and molecular genetics (micro) are getting mixed up in my brain.

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[lorenzomicron]

i think i've confused myself with a practice question but can someone explain to me:

let's say a condition/disease is recessive. because both genes are defective, no protein is made and something goes wrong physiologically. (correct?)

if a person is heterozygous for a gene, does that mean that one chromosome produces the protein and so everything is alright?? or something else happens?

If a person is heterozygous for gene, that means his genotype will be Aa, where A is dominant and a is recessive. In this case, if the defect is recessive a , then A will be expressed and yes, one of the alleles (coded on one chromosome) will be expressed as normal. in some cases, this is enough to overcome the effects of the defective gene when no protein is produced. in other cases, such as sickle cell anemia, the phenotype is seen to be a mix, with some normal proteins and some defective proteins. this is for the case where the trait is controlled by this single gene and additional additive or epigenetic effects are not considered.

the genetic material of each chromosome is a double helix, as you know, the complementary pair ladder. remember that each transcription and translation is a copy of one base of the complementary pair in the ladder, because of unzipping and things like that.

 

[docelh]

if a person is heterozygous for a gene, does that mean that one chromosome produces the protein and so everything is alright?? or something else happens?

The answer to both questions: it depends.

Sex chromosomes are included in that 46 number, btw. Not all genes are expressed. Some are near-permanently inaccessible.

 

[DrYoda]

if a person is heterozygous for a gene, does that mean that one chromosome produces the protein and so everything is alright?? or something else happens?

Sometimes. In recessive genetic disorders this is the case where the single gene can make enough of the protein for the body to funciton properly. In dominant conditions Heterogeneity means you have the disease/condition. There is also incomplete dominance and co-dominance both where you see distinct phenotypes with AA, Aa and aa individuals.

As the above poster said there are also cases where one of the genes is inaccessible (gene imprinting) but that, I suspect, is beyond the scope of the MCAT.