Question

1) You sequence a gene of interest and isolate the matching mRNA. You find that the mRNA is considerably shorter than the DNA sequence. Why is that?

a) There was an experimental mistake. The mRNA should have the same length as the gene.
b) The mRNA should be longer than the DNA sequence because the promoter is also transcribed.
c) The processed mRNA is shorter because introns were removed.
d) The mRNA is shorter because the signal sequence to cross the nuclear membrane was removed.

2) Why is it necessary that meiosis occurs in sexually reproducing organisms?

a) to maintain the viability of the gametes
b) to ensure that genetic variation is reduced
c) to maintain a constant chromosome number in each generation
d) to ensure evolutionary success

3) Explain how a boy could have his mother’s nose and his father’s ears.

a) independent assortment of chromosomes
b) the movement of homologous pairs during meiosis
c) by receiving his father’s Y chromosome
d) inheritance of intact chromosomes from parents

4) There are multiple ways that the diversity of offspring from the same parents is enhanced. What is the contribution of metaphase I to this diversity?

a) the random orientation of tetrads at the metaphase plate
b) the random alignment of homologous chromosomes when they cross over
c) the formation of chiasmata when the homologous chromosomes line up at the equator
d) the formation of a synaptonemal complex during chromosomal synapsis

5) Describe the general conditions that must be met at each of the three main cell cycle checkpoints.

a) G1 checkpoint - assessment of DNA damage, G2 - assessment of new DNA, M checkpoint - segregation of sister chromatids in anaphase.
b) G1 checkpoint - Energy reserves for s phase, G2 checkpoint - assessment of new DNA, M checkpoint- attachment of spindle to kinetochore.
c) G1 checkpoint - assessment of DNA damage, G2 checkpoint - energy reserves for duplication, M checkpoint - attachment of spindle to kinetochore
d) G1 checkpoint - Energy reserves for S-phase, S checkpoint - synthesis of DNA, G2 checkpoint - assessment of new DNA

Answer 1

1) The processed mRNA is shorter because introns were removed. (Protein coding information in gene is interrupted by non-coding sequence called intron.The entire DNA code is transcribed into pre-mRNA but this is edited into nucleus to give a mature mRNA)

2) To maintain a constant chromosome number in each generation. (Meiosis is reductional division which means that number of chromosome gets half.This process randomly shuffles genes across chromosomes and then randomly separate half of those chromosome into each gamete, and two gametes then randomly fuse to form new organism.)

3) Independent assorment of chromosome (when homologous chromosome pairs line up in random orientation at the middle of the cell as they prepare to separate.We can get gametes with different combos of mom and dad homologous i.e the alleles on those homologous because the orientation of each pair is random)

4) Metaphase I is identified when homologous chromosome line up in the middle of the cell,spindle fibre attach onto the homologous chromosome. Ans should be B

5) Ans- C