Question

1. In order to produce three glyceraldehyde-3-phosphate molecules that the plant could use to make other organic molecules, how many CO₂ molecules would have to enter the Calvin Cycle?

   		3
   		6
   		9
   		12

2. Genes A and B are on the same chromosome. If a person has one chromosome with the alleles AB and a second chromosome with the alleles ab, how could they produce a gamete with a chromosome containing the alleles Ab or aB?

   		independent assortment
   		random fertilization
   		crossing over
   		mitosis

3. There are several changes that occur to pre-mRNA in eukaryotic cells to produce the final mRNA molecule that will be used in translation. This process is called RNA processing. Which of the following occurs in the process of producing this final mRNA molecule?

   		a poly-A tail is added to the 5’ end
   		a modified guanine nucleotide is added to the 3’ end
   		the introns are cut out and the exons are attached to each other
   		none of the above

4. A mutation in a gene in the fruit fly Drosophila was found to affect eye color. The protein affected was found to be completely normal in its molecular weight and amino acid sequence, although much less of the protein is made in mutant flies. The most likely reason for the change in levels of protein is that the mutation:

   		occurs in the promoter of the gene, within several hundred base pairs of the start of transcription
   		is a change of a codon for serine into another codon for serine
   		is a frame shift mutation near the start of the coding region
   		affects the splicing of the mRNA

Answer 1

1. 9

Glyceraldehyde 3 phosphate = 3 carbons

3 molecules of glyceraldehyde 3 phosphate = 3 × 3 = 9 carbons

Calvin cycle is the process which leads to the formation of glucose by the fixation of atmospheric carbon dioxide. The key enzyme in this process is rubisco. The process is divided into three stages, carbon fixation, reduction and regeneration. It takes place in stroma of chloroplast.

2. Crossing over

When the genes are present on same chromosome they are said to be linked together. This is a type of non mendelian inheritance and is called as linkage. But still there are chances that genes present on one chromosome will swap with the genes present on the other chromosome. This is called as crossing over. It is the exchange of genetic material between non sister chromatids of homologous chromosomes resulting in the formation of recombinant chromosomes. This gives rise to parental and recombinant gametes. The number of recombinant gametes is much less than that of the parental gametes and is dependent upon the distance between the genes involved.

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