Biology question

[kbigboy]

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Hi guys,

From ADA practice test,

In diploid organisms, what does a single chromosome mean?

I don't know why "A single chromosome usually carries two alleles of each gene." is right.

Does a single chromosome mean homologous pair of chromosomes?

Please, help me out!!

 

[yzf600]

a single chromosome can consist of two joined sister chromatids.

this "single chromosome" has both of the same alleles since it is a duplicated structure...for example "A" ---"A"

However, after meiosis I (after crossing over with a homolog) a single chrom. can have two different alleles. "A"----"a"

 

[kbigboy]

Thanks, yzf600..

How about "At most only two alleles occur at a given locus in an organism genome"?
I am so confused....

 

[yzf600]

k...the locus is just the spot that a gene occupies on a chromosome.

for example, in humans there could be a specific locus (think location) for the eye color gene.

a "single chromosome", consisting of two chromatids can have one of each allele. (A)-----(a)....these are two different alleles, but there on the the same locus...the locus for eye color. These two alleles will determine eye color.

make sense?