Question

1) Describe what happens to the number of chromosomes during the two divisions of meiosis.

a)The number of chromosomes is halved in the first division of meiosis. In the second division, the number of chromosomes remains the same.
b) The number of chromosomes is doubled in the first division of meiosis. In the second division, the number of chromosomes is halved.
c) The number of chromosomes is halved in the first division of meiosis. In the second division, the number of chromosomes doubles.
d) The number of chromosomes remains the same in the first division of meiosis. In the second division, the number of chromosomes is halved.

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) 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.

6) 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

Answer:

1). c) The number of chromosomes is halved in the first division of meiosis. In the second division, the number of chromosomes doubles.

Explanation:

During meiosis I, Chromosome number is reduced to half whereas in meiosis II, the chromosome number in each cell is doubled.

2). c) to maintain a constant chromosome number in each generation

Explanation: Due to reduction of chromosome number in each cell after meiosis, chromosome number is maintained constantly in each generation.

3). a) independent assortment of chromosomes

Explanation: Due to independent assortment of chromosomes, some of mother and some of the father’s traits will appear in children.

4). a) the random orientation of tetrads at the metaphase plate

5). c) The processed mRNA is shorter because introns were removed.

Explanation: Immediately after the production, the mRNA is equal to DNA. Then the mRNA undergoes posttranscriptional modification, in which introns (non-coding regions) are removed and only exons are retained. Hence, the mRNA is shorter than the DNA.

6).

b) G1 checkpoint - Energy reserves for s phase, G2 checkpoint - assessment of new DNA, M checkpoint- attachment of spindle to kinetochore.