Sample ADA DAT # 28

[tokyoman]

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

1. At most only two alleles occur at a given locus in an organisms genome

2. Alleles occupy an identical locus in homologous chromosomes.

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

4. Single chromosome usually carries two alleles of each gene.

A.4
B.1 and 2
C.3
D.1,2 and 4
E.3 and 4

I thought 1 and 2 but the key says 1,2 and 4

can anyone explain why 4 is right?

Shouldn't homologous chromosome pairs (2 chromosomes) have 2 alleles?

and each chromosomes have one allele?

=( im confused

 

[nainaaz]

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

1. At most only two alleles occur at a given locus in an organisms genome

2. Alleles occupy an identical locus in homologous chromosomes.

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

4. Single chromosome usually carries two alleles of each gene.

A.4
B.1 and 2
C.3
D.1,2 and 4
E.3 and 4

I thought 1 and 2 but the key says 1,2 and 4

can anyone explain why 4 is right?

Shouldn't homologous chromosome pairs (2 chromosomes) have 2 alleles?

and each chromosomes have one allele?

=( im confused

Remember, a body cell has 46 chromosomes. This equates to 2 copies of EACH chrosomsome (2 times 23 = 46).

for the last option..
lets consider chromosome# 21...there are 2 copies of the same genes on chromosome 21 as there are two chromosome 21. So each one of that pair has two alternate forms of gene (alleles)...

hope it clarifies Ur doubt

 

[UCB05]

This question has been asked before, and the consensus opinion is that the question is either terribly worded or the answer is a typo. A "single chromosome" is a physical entity. One chromosome will have one allele of a gene while a distinct, separate homologous chromosome will have the other allele. Either the question meant to say "A single pair of homologous chromosomes..." for 4, or the answer is intended to be B

 

[Jia7]

I agree 4 isn't correct since each individual chromosome has only 1 allele of the gene and the homologous chromosome will have the other allele. If 4 was correct that would mean that you have 4 copies of the allele in the same organism and that is definitely wrong.

 

[gigawatt]

I completely agree. The only time that I can think of where #4 would be true is during the G2 phase (after DNA replication in S phase and prior to division in M phase). In that window, each chromosome consisting of two identical sister chromatids does, in fact, have two (identical) alleles for each gene.

 

[tokyoman]

This question has been asked before, and the consensus opinion is that the question is either terribly worded or the answer is a typo. A "single chromosome" is a physical entity. One chromosome will have one allele of a gene while a distinct, separate homologous chromosome will have the other allele. Either the question meant to say "A single pair of homologous chromosomes..." for 4, or the answer is intended to be B

thanks everyone =) I think the statement is poorly worded =)

I hope I don't get those kind of question on Real DAT because it's just not fair to get a question wrong that you know well.