Dec 14, 2009
423
1
0
Status
Pre-Dental
Q. Which of the following statements concerning alleles is true for diploid organisms?

I. at most only two alleles occur at a given locus in all organism’s genome
II. alleles occupy an identical locus in homologous chromosomes
III alleles of a given gene usually occur on homologous or non homologous chromosomes
IV a single chromosomes usually carries two alleles of each gene

correct answer is I and II

would you explain me in detail why other choices III and IV are incorrect statement?
 

dentalWorks

Nights Watchmen
7+ Year Member
Jun 25, 2009
5,646
157
181
Sterling Hts, Mi
Status
Dentist
Blue = my comments

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

I. at most only two alleles occur at a given locus in all organism’s genome
duh - this is genetics 101. Because we are talking about a DIPLOID organism, that means one set of chromosomes came from mom & the other from dad. To explain this further, think of a gene as something expressible, example of a gene is eye color. There are different variations of eye color, each variation is called an allele (for example, blue allele, green allele, brown allele, etc).

II. alleles occupy an identical locus in homologous chromosomes
Yes. Since we are talking about DAT genetics which is a very basic form of genetics, all alleles of a specific gene are occupied on the same location (same locus) of the two chromosomes (one chromo from mom & other from dad)... This figure might help you understand this better


III alleles of a given gene usually occur on homologous or non homologous chromosomes
The problem with this statment is the use of the word "usually" and "or non homologous chromosomes". You see, it is possible to have alleles be spread out on different chromosomes (non-homologous), but its not the "usual" form of how we study genetics. Basic Genetics (like the one you need to know for the DAT) is usually taught on the basis that the different forms of alleles for a given gene are all located on homologous chromosomes (like the figure I drew above)

IV a single chromosomes usually carries two alleles of each gene
A gene "USUALLY" occupies one locus on a chromosome and that locus will express the allele it carries. "USUALLY" the gene locus has 1 allele attached to it. So for example, the chromosome from mom has the allele "blue eye color" and the dad's chromosome has the allele "brown eye color"... It is unusual to see one locus having both alleles (both brown and blue color)

correct answer is I and II

would you explain me in detail why other choices III and IV are incorrect statement?
 
Dec 14, 2009
423
1
0
Status
Pre-Dental
Thank you for all of your hard work. I always appreciate for your effort. Anyway, I found the same question on different source which indicated correct answer is 1, II, and IV. Just want to let you know.
 

dentalWorks

Nights Watchmen
7+ Year Member
Jun 25, 2009
5,646
157
181
Sterling Hts, Mi
Status
Dentist
Thank you for all of your hard work. I always appreciate for your effort. Anyway, I found the same question on different source which indicated correct answer is 1, II, and IV. Just want to let you know.
your saying IV is correct? I am having a hard time with this cause thats like saying 2 alleles (blue and green eyes are on 1 chromosome).... The statement would be correct if it said "IV homologous chromosomes usually carries two alleles of each gene"

Do you mind showing me the source for this? Maybe there is something I missed when I studied genetics
 
Dec 14, 2009
423
1
0
Status
Pre-Dental
Its from old version of ADA sample test. There are two version for different year, but two have different answer. One has I and II and the one with recent year has a correct answer for I, II, and IV.
 

dentalWorks

Nights Watchmen
7+ Year Member
Jun 25, 2009
5,646
157
181
Sterling Hts, Mi
Status
Dentist
Its from old version of ADA sample test. There are two version for different year, but two have different answer. One has I and II and the one with recent year has a correct answer for I, II, and IV.
Oh... I really don't know what to tell you man...
If this was a test question on my DAT, I would pick I and II
 

OU11BB

10+ Year Member
5+ Year Member
Aug 7, 2008
366
4
91
Status
Dental Student
i go just 2 and 4. the only reason that i dont say 1 is b/c i recently had a test question very similar to this one and i picked true for the first. i ended up getting it wrong and when i went to talk to the professor he said that it was not just limited to two alleles and that 2 is most common but not always case.