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Questions on genes, alleles, and chormomes

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Questions on genes, alleles, and chormomes

Postby t4k9 » Wed Mar 09, 2005 3:31 am

What are the relationships between genes, alleles, and chormosomes? And how is DNA related to these? DNA has nucleotide sequences such as AGCT, and they make instrustion on protein creation. So, my question is, how does genes, alleles and chormosomes all relate to DNA? Thx for the answer in advance. While u r at it, i also want to ask, how is it expressed physically (genotype and phenotype)? I am really confused. I would approciate all answers, or redirects to any bio sites.
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Postby biostudent84 » Wed Mar 09, 2005 7:11 am

Genes: Bits of DNA that code for a particular trait.
Chromosome: A section of the DNA helix that is wound together into a "bundle" to save space
Allele: Two chromosomes that are homologous, or work with each other

Genotype: The genetic instructions for traits.
Phenotype: The expressed traits
Example: My mother has blonde hair, my father has brown hair. I carry both genes for blonde and brown hair, but since I only have one head, I can only have one hair color...that is brown =) My genotype is blonde and brown hair, and my phenotype is brown hair.

These are usually expressed in two-letter combinations. The first letter of the dominant trait capitalized represents the dominant trait, and the first letter of the dominant trait represents the recessive trait. (Yes, that is right...I didn't make any typo's there, lol)

If "B" is brown hair and "b" is blonde hair, and my genotype is brown and blonde hair, it is shown this way:

Bb

Each letter represents a gene from one allele. Since brown hair is dominant over blonde hair, brown hair is expressed.

See this:

BB

Both letters mean "brown hair" so this individual will also have brown hair.

Check it out:

bb

Both letters mean "blonde hair" so this individual will have blonde hair.

Let's see another example:
When Mendel first studied his pea plants, he noticed that tall plants were dominant over short plants. So "T" is the gene for tall plants and "t" is the gene for short plants.

TT

Both genes are dominant, and code for a tall plant. This plant is tall

What about this:

Tt

Same here as my brown hair...tall is dominant over short, so only tall is expressed.

Where do the short plants come from?:

tt

Both alleles say "short" so you get a short plant.

Wait! Where do these alleles come from? You get one allele from your mother, and the other from your father. These alleles are chosen at random when you are concieved.

Let's say Mom has the genotype "bb" for hair color and Dad has the genotype "BB" for brown hair. They have kids!

Because the alleles are chosen at random, the results will be as shown:

1/4 of all their children will have:
Phenotype: Blonde hair
Genotype: bb

1/2 of all their children will have:
Phenotype: Brown hair
Genotype: Bb

1/4 of all their children will have:
Phenotype: Brown hair
Genotype: BB

This can be shown more accurately by a "Punnett Square." These are neat little tools to determine odds of the genotypes and phenotypes any organism pair's offspring will have. Check this link out to learn more about them: http://www.borg.com/~lubehawk/psquare.htm

Kyle
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Postby t4k9 » Fri Mar 11, 2005 5:28 pm

thx for the reply. i understand the psquare now.

gene= {A,G,T,A,T,A...}
chromasome= {gene01, gene02 ...}
allele = {chromasome1a, chromasome1b} 2 chromasomes on different DNA
DNA = {chromasome1, chr2, chr3...}

This is what i get after reading ur post. Did i get it right? What does it mean when we say we have 23 chromasome pairs? is it 23 chromasome encodeded on each DNA strand?
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Postby biostudent84 » Fri Mar 11, 2005 6:15 pm

Not quite. Chromosomes are made up of DNA (and a few other molecules). Condensing DNA into 23 different pairs of chromosomes helps to organise the genetic information. When a protein needs to be made the cell thinks to itself "Hey! That information is on chromosome number 2!"
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Postby MrMistery » Mon Mar 14, 2005 8:18 pm

I've found out something new too. Kyle has brown hair :D
"As a biologist, I firmly believe that when you're dead, you're dead. Except for what you live behind in history. That's the only afterlife" - J. Craig Venter
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