Lab 4

Question 1

What are the phases of the cell life cycle?

Answer 1

1. Interphase - in between divisions; the cell is not dividing (this happens before both mitosis of meiosis)
2. Cell division - in the form of mitosis of meiosis

Question 2

What phase does a cell spend the majority of it life in?

Answer 2

Interphase

Question 3

Gap 1 interphase (G1)

Answer 3

Occurs immediately after a cell division.

The cell grows and performs all its routine metabolic functions (such as protein synthesis and organelle duplication)

Question 4

Synthesis interphase (S)

Answer 4

DNA replication is occurring

The DNA will partially uncoil and the strands separate at the H bond point. Each old base pair can now join with a newly made complimentary nucleotide and the H bond reforms. This continues till there are 2 identical molecules of DNA

Cell is now committed to performing some type of cell divi.

Question 5

Gap 2 interphase (G2)

Answer 5

Accumulation of energy is reserved to prepare for cell division

Question 6

What are the 3 substages of interphase?

Answer 6

G1 - Gap 1
S - Synthesis
G2 - Gap 2

Question 7

G0 phase

Answer 7

A variation of the G1 phase;

Cells that are destined to never be able to divide again

Ex. Mature nerve cells

Question 8

How do human chromosomes work?

Answer 8

Since we are diploid organisms we carry 2 copies of each unique chromosome, so the formula is 2n.

Humans have 46 chromosomes so the formula is 2n = 46 (with n being 23)
You receive 23 from each parent.

The 2 copies of the same chromosomes join together to form homologous pairs, but the gene contained in each chromosome may differ, which is called alleles

Question 9

Mitosis

Answer 9

The division of the nucleus.
The division of original parent cell nucleus makes sure that the chromosomal content of the 2 new daughter cells made by cytokinesis are identical to that of the parent cells.

Question 10

Cytokinesis

Answer 10

The division of the actual cell (division of the cytoplasm) to form two distinct new daughter cells.

(Accompanies the telophase part of mitosis)

Question 11

What are some functions of mitosis?

Answer 11

• human growth/development by forming new cells
• replaces or repairs worn-out, injured or dead cells

Question 12

Prophase (mitosis)

Answer 12

• chromosomes shorten and coil (become visible as individuals)
• centrosomes position at the poles of the cell and spindle fibres are being produced
• nuclear membrane begins to disintegrate
• kinetochore forms on the centromere

Question 13

Types of microtubules

Answer 13

Kinetochore - microtubules that grab onto the kinetochore protein found in the centromere
Nonkinetochore - microtubules that extend from pole to pole
Astral rays - help stabilize the spindle fibres, they reach to the edge of the cell

Question 14

Metaphase (mitosis)

Answer 14

• chromosomes meet in the middle (metaphase plate)
• each chromosomes is attached to the poles by the kinetochore microtubules
• nucleus disappears

Question 15

Anaphase (mitosis)

Answer 15

• sister chromatids of each chromosome are separated at the centromere.
• kinetochore microtubles pull the chromosomes towards the poles.
• nonkinetochore microtubules begin to elongate the cell (oval shape).

Question 16

Telophase

Answer 16

• chromosomes decondense
• as the nuclear membrane reappears, it forms 2 diploid nuclei each containing 2n unduplicated chromosomes.
• coincides with cytokinesis to produce to new daughter cells

Question 17

Meiosis

Answer 17

A nuclear division that creates haploid (n) gametes used for sexual reproduction.
(Haploid = half of the genetic info = 23 chromosomes)

Meiosis I - reduces genetic content from 2n duplicated chromosomes to n duplicated chromosomes

Meiosis II - same as mitosis but go from haploid to haploid

Question 18

Prophase I

Answer 18

Similar to mitosis:
- chromosomes condense
- spindle fibres start to form

Differences:
- chromosomes find their homologous pair (to form a tetrad) and lay side by side (synapsis) to get ready to exchange genetic info.
- crossing over occurs between nonsister chromatids in order to combine alleles.

Question 19

Synapsis

Answer 19

The members of each pair of homologous chromosomes move together, and lay side-by-side

Question 20

Crossing over

Answer 20

A form of genetic variability

Occurs in prophase I

As the homologous chromosomes lay side by side (synapsis), genes of nonsister chromatids are exchanged to create unique combination of alleles.

Question 21

Metaphase I

Answer 21

Similar to mitosis:
- chromosomes attached to spindle fibres and arranged on metaphase plate
- nuclear membrane disappears

Differences:
- chromosomes on the plate are arranged as tetrads(4 sister chromatids XX)
-independent assortment occurs because the arrangement on the metaphase plate is random

Question 22

Independent assortment

Answer 22

A form of genetic variation

Occurs in metaphase I

The orientation of each homologous pair along the metaphase plate is random. Genetic variation is made based on how the maternal and paternal chromosomes in each of the 23 pairs align.

Question 23

Anaphase I

Answer 23

Similar to mitosis:
- chromosomes have moved towards the poles

Differences:
- each half of a tetrad (X) is attached to a spindle fibre, so one X is taken to the left pole, one X taken to the right pole. (separation of XX tetrad).

Question 24

Telophase I

Answer 24

Similar to mitosis:
- chromosomes decondense
- formation of nuclear membrane
- cytokinesis forms 2 daughter cells

Differences:
- the nuclei of the daughter cells have only half as many (haploid) chromosomes as the parent cell had since it divided into 2 cells
- genetic variation created by crossing over and independent assortment

• you are left with 23 chromosomes and 46 chromatids

Question 25

Interkinesis

Answer 25

Resting period between meiosis I and meiosis II.

Similar to interphase, except no further DNA replication occurs

Question 26

Prophase II

Answer 26

Chromosomes condense and spindles form like usual, but this time the chromosomes are NOT crossing over

Question 27

Metaphase II

Answer 27

The chromosomes will line up in the middle on the metaphase plate but this time they are in singles not pairs

Question 28

Anaphase II

Answer 28

Chromatids of the chromosomes are pulled apart by spindle fibres and brought to their respective poles of the cell.

Question 29

Telophase II

Answer 29

Nuclei reforms and there are now 4 new daughter cells created after cytokinesis finishes the process off.

(4 new sperm cells if male, 4 new egg cells if female)

You now have 23 chromosomes and 23 chromatids

Question 30

Homologous chromosomes

Answer 30

A pair of chromosomes with one chromosome provided by the maternal side and one by the paternal side. They carry the same gene and have identical centromere position