BIO Questions from ADA sample booklet

[jeminizz]

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28. Which of the following statements concerning alleles is true for diploid organisms?
1. At most only two alleles occur at a given locus in a 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.

 

[chordata]

28. Which of the following statements concerning alleles is true for diploid organisms?
1. At most only two alleles occur at a given locus in a 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.

All are true except #3.

 

[mccarth2]

I remember I got this one wrong on the ADA test & it really upset me. For #4 the two alleles that occur at the same locus, aren't they on different homologous chromosomes vs. one "single chromosome" (as stated in 2). Otherwise wouldn't the genotype be AAAA vs. AA. Needless to say I put B for 1 & 2.

 

[jeminizz]

yea i thought it was B (1,2) also... I dont' know if its me only but i think some of the ADA questions are poorly worded. I wonder if it is like that on the real test. I still don't get why choice #4 is true. Can someone explain? Thanks...

 

[786mine]

does diploid NOT mean the double number of chromosome rather the gene (which the allele control)?

haploid - half
diploid - double. right?

 

[fannian]

if the answer is 4, then i think i know why (if the answer is NOT four, then sorry for confusing you more)

but each chromosome has only one locus for any partucular allele.

Of course - there exists alternate forms of genes (which are alleles) - but one allele will be on the maternal chromosome, and another maybe on the paternal chromosome.

Think of blood groups - that's how i make sense of it!

A allele, B allele, i allele (are all alleles - alternate forms of a gene):

The first letter represents the allele on the paternal chromosome, and the second letter on the maternal:

A A (homozygous individual)
A i (heterozygous)
B B (homozygous)
B i ( heterzygous)
i i (blood type O)


Now - could someone explain to me about antigens, and all that stuff, and how blood transfussions work, i'd be gratefull!