Which statement concerning alleles is true for diploid organisms?

[bnleong]

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. A single chromosome usually
carries two alleles of each gene.
A. 4
B. 1 and 2
C. 3
D. 1, 2 and 4


The answer key says D but I still think its B. I thought that a single chromosome carries 1 allele. But a homologous pair of chromosomes will have a total of two alleles. Am i wrong?

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[2PacClone23]

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. A single chromosome usually
carries two alleles of each gene.
A. 4
B. 1 and 2
C. 3
D. 1, 2 and 4


The answer key says D but I still think its B. I thought that a single chromosome carries 1 allele. But a homologous pair of chromosomes will have a total of two alleles. Am i wrong?

Yeah D def. the whole non homologous thing throws me off.

 

[bnleong]

??? so u think its D still?

 

[txlonghorn]

Bad question, but I trust the ADA to maybe have better questions on the DAT. D can be right if you think of the chromosome as having sister chromatids. In that case, there will be 2 alleles present - of the same type. As I said, bad question.

That test also had an error on the gchem section where it gave the electron config for an atom and asked how many unpaired electrons there were it was something 3p2, which obviously has 2 unpaired electrons, but the answer was 3.

 

[ZFT]

The cell cycle consists of G1, S, G2, and M phases - the only time sister chromatids are split is after metaphase, so it's only for a brief time in the life of a diploid cell when the two alleles are actually split on two chromosomes (2 kinetochores). Notice the word "usually" in choice D.

 

[Baylor2011]

This question was discussed back in May, concluded it was a bad question.

 

[UCB05]

The cell cycle consists of G1, S, G2, and M phases - the only time sister chromatids are split is after metaphase, so it's only for a brief time in the life of a diploid cell when the two alleles are actually split on two chromosomes (2 kinetochores). Notice the word "usually" in choice D.

Anaphase/telophase may be the only time two allele copies on replicated chromosomes in a single cell are separated, but 4 is false through all of anaphase, telophase, and most importantly, G1, which tends to be the longest phase of the cell cycle, sometimes even arresting into a G0 phase, so it's a bit of a stretch to say this phase is a "brief time" in the cell cycle. I would not consider only S, G2, and half of mitosis to be "usually"

 

[ZFT]

Anaphase/telophase may be the only time two allele copies on replicated chromosomes in a single cell are separated, but 4 is false through all of anaphase, telophase, and most importantly, G1, which tends to be the longest phase of the cell cycle, sometimes even arresting into a G0 phase, so it's a bit of a stretch to say this phase is a "brief time" in the cell cycle. I would not consider only S, G2, and half of mitosis to be "usually"

Maybe it's a pie chart problem - which is greater: G1 + 1/2M or S + G2 + 1/2M...

Edit
actually for mitosis, two alleles never appear on the same chromosome, only two copies of a single allele - one on each sister chromatid. Only a tetrad in meiosis would have both alleles.