Education Genetics

Hi all, trying to get some genetic stuff sorted in my head before I return to college, and I'm hoping you can all help me.

In geneticss, can it be said that:

Codons are composed of three bases

Alleles are composed of any (within reason) number of codons

Chromatids are formed by lots and lots of alleles

Chromosomes are formed by two chromatids (except during 2nd stage meiosis)

Genomes are formed by the full number of chromasomes found in a cell.

Also, genotypes describe all characteristics of a genome(?), whether expressed in the lifeform or not. While phenotypes describe only the characterists of a genome that are expressed in a lifeform. Lastly, a diploid cell has four pairs of chromosomes, while a haploid cell has only two pairs of chromosomes.

That all correct? If not, what have I got wrong? And have I missed anything obvious? This is a subject that I really find fairly confusing. It just won't all fit together in my head the way I need it to. At least not yet. Cheers for any help.

 

Genes are composed of any number of codons. Alleles are different versions of that same gene (maternal and paternal). Chromatid is essentially half a chromosome, a bunch of genes surrounded by a protective protein. The genome is all the genetic code.
AFAIK the phenotype is a visible expressed characteristic (eye colour) while the genotype is non visible characteristic (blood type). A diploid has the full set of chromosomes, one from your mother and one from your father. A haploid cell only contains the one, so either your materal or paternal.

(All from memory, so don't blame me if some is incorrect)

 

Cheers. Think that mostly chimes with what I understood to be the case

 

All correct.

The genotype describes the specific genetic makeup of an individual (which distiguishes this individual from other members of the same species).

The phenotype describes any observed quality of an organism, such as its morphology, development, or behaviour; how a person looks, basically. The phenotype is not just the product of the person's genotype, but also of environmental, non-genetic developmental factors.

Diploid cells have two homologous copies of each chromosome, usually one from the mother and one from the father. These chromosome pairs can be present in any number. Humans, for instance, have 23 pairs.

Haploid cells are a bit more tricky. Originally the term "Haploid" was used interchangably with "Monopoloid". In monopoloid cells chromosomes do not occur in pairs, but singly.

However things are now more complicated:

 

So a human diploid cell will have 46 pairs of homologous (homologous basicly = identical?) chromosomes then, 23 from each parent? Your wikipedia quote just confuses the hell outta me. Odd that this stuff does that to me so much. I guess i just need to read it all again another 400 times

edit: Yup, makes sense now. For humans haploid as good as equals monoploid, so I'll stick with that simply because to do otherwise would add more confusion to an already terminology laden subject.

Cheers

 

No, 23 pairs = 46 chromosomes. 23 from each parent.

 

If I was being pedantic, I'd say that an allele is more of a functional unit than an anatomical one. Billions of base pairs go to make one cromatid, but not all of these form alleles. As you're probably aware, a large proportion of the genome (as currently understood) is 'junk' (or introns) - the bits between functional genes (exons). Introns are not alleles, so to say chromosomes are made up of alleles is like saying a cup of tea is made from tea leaves - yes the tea leaves are the important bit, but that's not the whole story. Sorry I couldn't come up with a better analogy

An allele is really only relevant in terms of genetic function - for simply understanding the anatomy of everything, you can omit the idea of an allele.

Did you mean heterologous?

EDIT: Hmmm I see you got that from Wikipedia. Wikipedia can't be wrong... Can it?

EDIT2: It would seem that in the context of chromosomes, homologous doesn't mean identical. Kinda confusing.

 

No sh*t, Sherlock.

Actually, "junk" DNA has been found to be not so useless after all. If exons are the leaves, introns are the hot water. For this reason the term "allele" is also used to refer to non-gene coding DNA.

No, I really meant homologous.

It can be, but people who know the meaning of "homologous" can generally interpret the text critically and filter out the bad bits.

I think you are getting confused with "homogenous". Homogenous = identical; homologous = having the same function.

 

and once again Nexxo comes and proves he is the almighty when it comes to everything

 

No, I'm just a smartass.


Hey, at least I've got insight.

 

I didn't think that was clear from the above posts, sorry if I was stating the obvious.

Disagree. If an allele is one form of a gene (and it is), then it doesn't refer to non-gene coding DNA. Like I was trying to say with the analogy, the hot water is obviously still very much important important for the tea.

You're right, I know so-called 'junk' DNA isn't all junk. What I meant is that DNA is not comprised entirely of genes (or alleles) - there's other 'stuff' there too. And yes, you're right, the other stuff isn't all junk. I must be more careful with semantics when I argue with Nexxo

Ah, maybe - Thanks for clearing that up. Need to brush up on my latin...

 

Actually, even dictionaries can get vague on this, confounding similarity of structure vs. that of value, appearance, function...

 

That's Greek you'd need to brush up on. The Latin was a transliteration.

 

I took this in 10th grade biology

 

So?

 

all of what you said looks correct

 

Everyone could be a smartass if they "wanted to be" i.e. myself.

But people (like myself) cba with all that rubbish.

 

Concepts, people, not words

You posted a simple set of questions and got definitions. Well, you asked for it. If you want to really review your genetics knowledge, don't try to remember it all at once. Try out a site such as the Genetic Science Learning Center at the U of Utah or go to Second Life. There are lots of good basics out there that don't dump you into arguments about individual words. With the statements you made, structured demos will bring you more rapidly up to a stage where you can really jump into things.

 

Me too, but it comes up repetitively if you take any college level biology courses. Always good to keep it fresh.

 

He asked for clarification on definitions, so yes, definitions is what he got.

Still, thanks for the links; they are useful also.