DAT question help!

[savvysearch]

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This question is confusing to me.

Which of the following statements concerning alleles is true for diploid organisms?

1 At most only two alleles occur at a given locus in an organism's genome.

2 Alleles occupy an identical locus in homologous chromosomes

3Alleles of a given gene usually occur on non-homologous chromosomes.

4 A single chromosome usually carries two alleles of each gene.

A 4

B 1,2

C 3

D 1,2,4

E 3,4

Answer is D. I put B. What?!

Number 1 and 2, I get. But number 4 I don't. Aren't there only one allele per chromosome? One allele on the chromosome you get from dad (R) and one you get from mom (r)
so that you get a total of two alleles (Rr) and two chromosomes.

 

[AcidETCH]

Actually the 4th statement is vague as it would depend on the cell cycle.

To answer your question, I believe that a chromosome in a certain part of the cell cycle will be made up of 2 chromatid sisters. Each chromatid sister will have 1 allele. That's why a chromosome will usually have 2 alleles of each gene. Hope that helps.

AE

 

[TechDent]

Basically an allele is an alternative form of a gene. For example the allele for height can have two forms. Short and Tall. Usually there are two forms of the gene or alleles. Although there are exceptions. Since the question says usually then it counts as a correct answer. Hope this helps.

 

[damian12]

A single chromosome WILL NOT usually carry two alleles of the same gene, but homologous chromosomes could carry alternative forms of a given gene. A chromosome is a condensed supercoiled version of DNA complexed w/ histones which is about to undergo mitotic division, BUT the situation could get tricky if you take into account the S-phase as mentioned by Acid. Now sister chromatids are present and identical copies of a gene exist alongside eachother AND this still consitutes a chromosome - in humans, 46 of 'em. Remember, the DNA content has doubled, but the number of chromosomes haven't !!

Anyways, that question is poorly worded !! Hope this helped a bit Savvy !! 😉