Question

9. Imagine an organism with a diploid number of 16. How many chromosomes would be present in a typical cell during the G1 phase of the cell cycle? (Just give a number!)

10. Imagine an organism with a diploid number of 16. How many chromatids would be present during the G1 phase of the cell cycle? (Just give a number!) (2)

11. Imagine an organism with a diploid number of 16. How many chromatids would be present just before the cell goes through mitosis? (Just give a number!) (2)

12. Imagine an organism with a diploid number of 16. How many chromatids would be present in each (one) daughter cell at the end of mitosis? (Just give a number!) (2)

13. Imagine an organism with a diploid number of 16. How many chromatids would be present just before the cell goes through meiosis (just give a number!)? (2)

14. Imagine an organism with a diploid number of 16. How many chromatids would be present in each (one) daughter cell at the end of meiosis? (Just give a number!) (2)

15. EXPLAIN the difference(s) between a dyad (double-stranded chromosome) and a pair of homologous chromosomes. Include the concept of "genes" and “alleles” in your answer.

16. What do we mean when we use the phrase “reduction division” (what is the significance of the “reduction division”)? When does the reduction division occur?

17. The ability to hear is dependent on two different genes (gene “E” and gene “H”). An individual must possess at least one dominant allele for each gene in order to hear (not be deaf).   If the individual is homozygous recessive for either gene, that person will be deaf. A deaf man marries a deaf woman and all of their 7 children can hear. What are the genotypes of the two parents?

Answer 1

Phases of cell cycle includes:

• Interphase: It is the preparatory phase and is further divided into 3 phases.

A) Gap 1 or G1 phase: Cell grows rapidly. New organelles, proteins are synthesized.

The cell attains a larger size, ribosomes are increased, proteins for division are produced.

G1/S checkpoint checks that all the required materials for division are present.

B) Synthesis or S phase: DNA replication occurs, chromosomes within the nucleus are copied. Chromatids are formed.

C) Gap 2 or G2 phase: Organelles (chloroplast, mitochondria are replicated).

G2/M checkpoint, before mitosis, checks the chromosomes.

• Mitosis: Sister chromatids separate. Nucleus divides.
• Cytokinesis: Two new cells are formed
• Here chromosome number of the diploid cell, 2n =16. The number of chromosome before S phase is 16 and chromatids are also 16.
• After S phase, chromosome number remains same = 16, chromatids are doubled =2 x 16 =32.
• After cytokinesis in mitosis, each daughter cell will receive 16 chromatids.
• During meiosis,  4 genetically diverse haploid nuclei: In meiosis II, after cytokinesis, 4 genetically haploid cells are produced. Thus, 2n becomes n.
• Hence before start of meiosis, chromosome = 16.
• After meiosis, chromosome in each haploid daughter cells is 16/2 =8

Answers:

9. 16

10. 16

11. 32

12. 16

13. 16

14. 8