What is the difference between recessive and dominant diseases?

Question

I am doing an assignment on 'Genetic and Chromosomal Abnormalities' for year 12 and one of the questions asks for "the difference between recessive and dominant diseases?" I have found some information but am struggling to combined what I have to form a conclusive answer.

I would really appreciate any site links or other information you could provide..

Thank you!!

Answer 1

One thing that may help is to simply use the wikipedia to look up both recessive and dominant, sure its not a great primary source if your doing top of the line research but it works well enough for this certainly. Also it may help to have two diseases in mind when thinking about this, I'll go with old favorites such as Huntington's and why not the good ol sickle cell. An important note I will be talking about things that relate mostly to autosomal dominant and recessive characteristics, these rules also work for X-linked but that whole X-linked factor adds confusion at times.

Ok as you have probably picked up dominant means that if you get even one chromosome from one parent with the abnormal gene then you will suffer the disease. Oh as a quick heads up though I'm assuming you mostly have this down you have 22 pairs of autosomal chromosomes (and then the 1 pair of s*x chromosomes), and from each of these pairs you have received one chromosome from each parent. Recessive diseases require both chromosomes from a given pair to be abnormal in order for the individual to suffer the disease.

Try to look up some autosomal dominant and autosomal recessive family trees and you can get a picture of what happens in a family and start to get an idea of the differences between the two.

You will notice that recessive diseases can "skip" generations, where a parent has the disease, the children seem to be unaffected and then their children perhaps end up with the disease. This is because the chromosome, lets say chromosome 14 for clarity, with the abnormal gene was passed on to this person, but because they had one normal gene on the other chromosome 14 they did not have the disease. The reason this is is because the normal gene on the normal chromosome can make up for the underperforming gene, essentially the abnormal gene has lost its ability to create a working protein. Really briefly this is why men suffer from the X linked recessive diseases so much, they dont have the second X chromosome and therefore lack the normal gene that may have been on it. If they get an abnormal gene that lost its ability to function then there is no other gene to take up the slack

With a dominant disease if you have the abnormal gene on one chromosome then you will have the disease, it doesnt matter if the other gene on the other chromosome is normal. This is why this disease can't skip generations, though, if a child has the abnormal gene then you know he has it because he will get sick. With recessive the child may have one abnormal gene but without having abnormal genes on both chromosomes they will not be sick, only their offspring will if the person they marry also happen to have an abnormal gene on their chromosome.

So to clarify this really quick, recessive disease means that the abnormal gene has lost its function. What happens in a dominant disease is that usually the abnormal gene has gained a harmful function. This is key to how I was able to wrap my head around it, the gene itself is abnormal in both bases but with recessive its lost the ability to do anything and with dominant its actually gained the ability to cause you harm. This may not help you learn it, but I think once I was able to start getting it this really helped clarify what was happening.

So we can look at our two examples, sickle cell anemia has a loss of function mutation in the gene, so if you get one abnormal gene your fine because you have a normal healthy gene on the other chromosome that can take up the slack. Though not always perfectly, but well enough usually.

With Huntington's disease the abnormal gene has now become directly harmful to your health, its like a poison now and having even jus the one abnormal gene means you will get the disease. The protein made from this gene causes harm to your body, the fact that you have a normal form of the gene is meaningless because the normal gene can't fix this new problem, this new function that the gene was never supposed to control.

Wow, sorry this was incredibly long but maybe it helped

Answer 2

A recessive gene is a form of a gene that, when present along with the dominant form, is not expressed.

Genes are segments of DNA that are located in a specific spot on a chromosome. Diploid organisms get a chromosome from each of their parents.

Without going into too much detail, mutations can change the expression of a given gene, and these genes can be passed down to successive generations. In a dominant-recessive relationship, (as opposed to the law of codomonance, incomplete dominance etc...) If present, the DOMINANT gene will be expressed regardless of the other gene on the other corresponding chromosome.

Although the dominant gene will be expressed if present no matter what, if the other gene is present it is carried by the individual in their DNA and when that individual reproduces there is a 50% chance that the recessive gene is passed down from that individual.

The only way that a recessive gene is expressed phenotypically is if the individual, or organism, receives two copies of the recessive gene; that is, they do not possess a copy of the dominant version of the gene.

Answer 3

I am not sure if this is what you mean but its a slight variation on the previous answers.

Think of a recessive trait as something that is NOT coded for eg something missing, that is present in the dominant trait.

when you get a dominant allele, the chemical, feature etc is coded for and the result is that a recessive disease is masked as a result.

when you get both recessive alleles, the "thing" is not coded for and you don't get something formed correctly.eg in cystic fibrosis the cells in the lung are incorrectly made and there are some other issues.

its the same for say albinism, where there are some stages in the process of making pigments are missing.

The only real dominant trait disease i can think of off the top of my head is huntingtons, i am not sure what is coded for which causes it, but there must be something.

Hope it helps  

Answer 4

simply a recessive disease is a genetic disease that affects the recessive gene and does not exhibit sympotoms unless you are homozygous recessive for the gene but can still be inherited by a future generation.  

A dominant one is one that affects the dominant gene and will show symptoms if you are heterozygous or homozygous dominant for the gene.