1) 4pts – When telomeres get short, the cell has two options – either senesce or die during crisis. Define these 2 terms and their stories – [what happens to the cell?].
2) 5pts - Discuss the mechanism by which the two-part telomerase enzyme maintains telomere length. What differs between a young and a mature person’s telomerase expression? How might aging fit into this discussion?
3) 6pts - Distinguish which gene loci are linked versus unlinked. Is the loci “scarlet eyes” linked to one or both of the other loci? If the data suggests linked, how far apart are the loci in cM, and are the dihybrid parent’s alleles in the coupled or repulsed haplotype conformation? Assume the traits are both autosomal recessive. Show your MATH calculations!
Wt dihybrid x hairy body [hb], scarlet eyes [se] wt dihybrid x scarlet eyes [se], bent wings [bw]
Offspring #s Offspring #s
wt 9 wt 28
hb 39 se 22
se 41 bw 23
hb & se 11 se & bw 27
100 100
Ans. 1. Telomere are the ends of the chromosome.
During shortening of telomere it leads to 2 actions namely
I. Death called Apoptosis or programmed cell death.
Telomere uncapping occurs when telomeres are shortened.
Telomerase has the ability to extend telomeres, and is present in germline and certain hematopoietic cells, whereas somatic cells have low or undetectable levels of this activity and their telomeres undergo a progressive shortening with replication. Telomerases are reactivated in most cancers and immortalized cells.
Senescence - Telomeres shorten as a result of cellular replication, leading to a permanent cell cycle arrest, also known as replicative senescence.
Ans 2. Telomerase is a reverse transcriptase enzyme that carries its own RNA molecule which is used as a template when it elongates telomeres. Telomerase is active in gametes and most cancer cells, but is normally absent from, or at very low levels in, most somatic cells.
Telomerase can bind the first few nucleotides of the template to the last telomere sequence on the chromosome, add a new telomere repeat (5'-GGTTAG-3') sequence, let go, realign the new 3'-end of telomere to the template, and repeat the process.
Telomerase reverses telomere shortening.
Telomerase and ageing- Telomeres get shorter each time a cell copies itself, but the important DNA stays intact. Eventually, telomeres get too short to do their job, causing our cells to age and stop functioning properly. Therefore, telomeres act as the aging clock in every cell.
1) 4pts – When telomeres get short, the cell has two options – either senesce or...