Locus, Gene, Allele

[Ashish]

1. B - Organisms that are diploid have two copies of each chromosome. For example, human body cells are diploid containing 23 pairs of chromosomes, with one chromosome being inherited from each parent. For a given locus or location on a gene, there are at most two types of alleles, which could either be recessive and dominant. One pair of chromosomes often carries two alleles, either two recessive alleles (homozygous recessive), two dominant alleles (homozygous dominant), or one dominant and one recessive allele (heterozygous). This is “usually” true as some traits may involve multiple alleles, more than just a dominant and a recessive, as is the case with blood groups. Likewise, the alleles that code for the same gene are located in identical areas on homologous (related chromosomes). A single chromatid only contains one copy of an allele.
   
   The above is the the explanation to the answer for Question 28 on Bio in 2007 DAT. I am having a hard time understanding this simple topic of alleles and genes.
   
   So my question is a haploid chromosome still has 2 alleles in a locus since a chromatid only has 1 copy of allele?

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[matteral]

1. B - Organisms that are diploid have two copies of each chromosome. For example, human body cells are diploid containing 23 pairs of chromosomes, with one chromosome being inherited from each parent. For a given locus or location on a gene, there are at most two types of alleles, which could either be recessive and dominant. One pair of chromosomes often carries two alleles, either two recessive alleles (homozygous recessive), two dominant alleles (homozygous dominant), or one dominant and one recessive allele (heterozygous). This is “usually” true as some traits may involve multiple alleles, more than just a dominant and a recessive, as is the case with blood groups. Likewise, the alleles that code for the same gene are located in identical areas on homologous (related chromosomes). A single chromatid only contains one copy of an allele.
   
   The above is the the explanation to the answer for Question 28 on Bio in 2007 DAT. I am having a hard time understanding this simple topic of alleles and genes.
   
   So my question is a haploid chromosome still has 2 alleles in a locus since a chromatid only has 1 copy of allele?

A haploid isn't a chromosome, it's a type of cell. A haploid cell only has one allele for each gene since it only has one chromosome (unless that gene was duplicated in the chromsosome)