Question

sickle cell anemia is caused by a missense mutation in the β - globin gene. the normal allele of the β - globin gene is located near the left end of chromosome 2. if someone has one normal allele and one mutant allele, where are they located? hint: draw out each answer choice so you understand what each is saying. one is located on the left end of one chromosome 2, the other is on left end of the homologous chromosome. one is located on the left end of one chromatid of chromosome 2, the other is on the left end of the other sister chromatid. one is located on the left end of chromosome 2, the other is on the left end of a non - homologous chromosome. one is located on the left end of chromosome 2, the other is located on the right end of the homologous chromosome. one is located on the left end of one chromatid of chromosome 2, the other is located on the right end of the other sister chromatid.

Explanation:

Alleles are alternative forms of a gene. Homologous chromosomes are pairs of chromosomes (one from each parent) that have the same genes at the same loci. Since the normal allele of the β - globin gene is located near the left end of chromosome 2, the mutant allele (as an alternative form of the same gene) will be at the same locus (near the left end) on the homologous chromosome. Sister chromatids are identical copies (after DNA replication) and would have the same allele (if no mutation occurred during replication, which is not the case here as one is normal and one is mutant). Non - homologous chromosomes have different sets of genes. Also, alleles of the same gene (normal and mutant here) should be at the same locus (near the left end) on homologous chromosomes.

Answer:

One is located on the left end of one chromosome 2, the other is on left end of the homologous chromosome.