How would a haploid chromosome dna look like??

ARAVIND113122

how would a haploid chromosome dna look like?will it be a single strand of DNA from a single parent? or will it be 'bits and pieces',with gaps in between.the purpose of asking this question is i don't understand how haploid chromosomes 'fuse' to form a single embryo.

Ryan_m_b

Short on time atm but I'll refer you to meiosis.

mishrashubham

A chromosome is one long molecule of double stranded DNA. So haploid means having only one copy of a chromosome but it is still dsDNA. No it will not be in bits with gaps in between. You probably think of DNA being arranged in pieces and then joined with molecular glue to form chromosomes when gametes fuse. That is not the case. They remain intact as long molecules, just that the resulting zygote has now two copies of each chromosome i.e. it becomes diploid. The chromosomes themselves do not physically fuse into one.

ARAVIND113122

Then how does rna polymerase produce mrna that encorporates charecteristics from both the father and the mother??...i.e..if the two chromosomes[which contain genes from different parents] are 'far away' from each other,how does each chromosomes contribute in making the same protein??
If both father and mother chromosome takes part in transcription and translation....how does the body 'decide' which gene is dominant and which recessive?

basalt

It doesn't, mRNa will come from only one copy of a gene. If you have two copies of a gene, one paternal and one maternal it is possible that both will be expressed and if one carries a mutation and one doesn't then both mutated and wild type protein may be present ( best example I can think of is sickle cell anaemia vs sickle cell trait ).

This isn't always the case though - some genes are expressed from one or the other chromosome but not both in which case one copy will be turned off ( such control is by DNA methylation ) - you're into epigenetics here, such controls can be random or regulated - look up X inactivation for a good example and many pictures of cats.

Dominant or recessive is a feature of how a particular gene works not of whether the body decides to make something dominant. If a particular gene is there to turn on a particular metabolic pathway ( say, to make purple pigment for petals ) then it doesn't matter whether there's one copy or two - any amount of the gene product will turn on production so the trait is considered dominant. Both gene products are still being made but one is masked.

ARAVIND113122

if the rna created by both the pairs of chromosomes are nothing but nucleotide bases which code for amino acids,why are some genes dominant while others recessive?

mishrashubham

What's important here is not the that they are made up of nucleotides but the fact that they are arranged in a particular sequence. Two different alleles of the same gene have different sequences such that they also result in a different a polypeptide sequence and this should have an effect on the function of the protein.

Let us take just two alleles of a gene, namely A and B. Let A produce a functional protein X and B its non-functional version resulting in phenotypes P and Q respectively.. If suppose a person has alleles A and B, B will be recessive if the amount of X produced is sufficient to fulfill the body's needs with thus having phenotype P. A will become recessive if amount of X produced is does not fulfill the requirement giving phenotype Q.

Alternatively B can produce a version of X that has lower efficiency than the original X, such that A alone is insufficient. Then the resulting phenotype will be somewhere between P and Q.

ARAVIND113122

thank you very much

Miracles815

Aravind113122....DNA is, through a series of steps, responsible for synthesizing proteins. After all is said and done with ribosomes and RNA, it was the DNA that had the initial code to make the protein. A gene is a segment of bases on a DNA molecule that makes a specific protein. The above answer to your last question is pretty wordy, and sometimes in Science you just have to let your mind fill in the gaps. No matter what anybody tells you, science is not absolute. So say that a multitude of genes code for the shape of a seed. Some genes code for a wrinkled seed, while some code for a smooth seed. One of the specific base codes will, in a sense, cancel out the other. So therefore, assuming smooth seed gene cancels out the wrinkled, you would need all wrinkled genes to to have wrinkled seed in appearance. If the dominant form of the gene, contain the smooth code, was present, it would cancel out the wrinkled code. Therefore, the smooth genes are said to be dominant because of their unique sequences of bases that allow them to be more efficiently used over the wrinkled seeds, kind of like choosing a fresh apple over a rotten one. We choose the fresh apple because it is more appealing, and the coding process chooses the dominant gene when it is present because it is more appealing. The only way we would choose the rotten apple (recessive gene) is if we were choosing between two rotten apples, and the only way we wouldn't choose the fresh apple (dominant gene) is if it wasn't there. If you want to dive deeper into the chemical basis that makes the dominant more appealing, buy some books.

mishrashubham

While multiple genes can be (and usually are) responsible for a particular phenotype, the talk is about dominant and recessive alleles of the same gene.

Please elaborate on what you exactly mean by "base codes cancelling each other out".

Both the alleles are transcribed roughly equally in the body. So dominance of traits is usually not due to difference in the transcription levels although allele specific transcription factors do exist. In that case epigenetic factors would also come into the picture.

Miracles815

I could have used one gene to answer the question, but its not really correct to say "the gene for wrinkled/non wrinkled...not a big deal the way I worded it. Next question...In the end, after all is said and done, one gene did cancel the other out. Sure, there is much, much more to it, but I dont think the original poster is looking for that. So, essentially, the dominant gene does cancel out the recessive. And I dont understand your problem with my last point because the part you highlighted is correct.

bobze

No, like Mish pointed out, in the case of these genes they are both transcribed still. Only one phenotype is displayed though--Not a mixture of both. When this happens one gene is said to be "dominant" to the gene.

Of course, most genes don't work so simply. Sometimes proteins are composed of multiple subunits, so phenotype with a mixture of genes is expressed. Sometimes genes are expressed in different amounts (hemoglobin is a good example of this) and other times one allele will interact with another (dominant negative expression for example).

It would be incorrect to describe to someone learning biology that a "dominant gene cancels out a recessive gene".

Miracles815

Sorry, but you are wrong. Yes, recessive genes are still transcribed, but in the final phenotype, the dominant gene is displayed. Therefore, relative to the phenotype, the recessive gene was "cancelled out." These words can be used as a simplified way of describing what occurs. The presence of one gene prohibits an allele from being shown in the phenotype. Therefore, it cancelled it out. Sure its simplified because the recessive allele was still transcribed, or "made." But cancelled out simply implies that the existence of one thing prohibits the existence of something else. That is exactly what happens here, at least in the phenotype. This overall explanation of the phenomenon is fine if explaining the concept to a Biology learner because it gives them an overall end game of the processes, and this is where teaching begins. Kind of like we were all lied to in high school about the exact locations of electrons within an atom. Sometimes, in order to move forward, things are taught extremely simplified, which some would refer to as "wrong."

mishrashubham

It is not about how you said it. Talking about the relationship between different genes is not the same as talking about the alleles of the same gene.



My point was that dominance is mostly not because of difference in transcription levels of the alleles.

The OP was probably asking about the molecular basis of dominance and not what its logic is, judging by the fact that he was satisfied with the explanation.

Which is why I asked you to clearly define whatever you wrote instead of calling it wrong. Anyways, using words such as 'cancel' in such context makes it extremely vague and can give a wrong idea about the concept.