Chapter 16

Question 1

What are the four main phases of the cell cycle?

Answer 1

G₁, S, G₂, and M phase.

Question 2

What happens during G₁ phase?

Answer 2

Cell grows, performs normal functions, and commits to divide if conditions are right.

Question 3

What happens during S phase?

Answer 3

DNA is replicated — each chromosome forms two sister chromatids joined at a centromere.

Question 4

What happens during G₂ phase?

Answer 4

Organelles replicate, microtubules form, and proteins needed for mitosis are made.

Question 5

What happens during M phase?

Answer 5

Mitosis (division of nucleus) and cytokinesis (division of cytoplasm).

Question 6

What is the G₀ phase?

Answer 6

A non-dividing resting phase; some cells enter permanently (e.g., nerve cells).

Question 7

What is interphase?

Answer 7

Includes G₁, S, and G₂ phases — when the cell grows and prepares to divide.

Question 8

What is the spindle apparatus made of?

Answer 8

Microtubules formed from centrosomes (microtubule-organizing centers).

Question 9

What are the three types of spindle microtubules?

Answer 9

• Astral (position spindle) * Polar (push poles apart) * Kinetochore (attach to centromeres)

Question 10

What is the centromere?

Answer 10

The region where sister chromatids are joined.

Question 11

What is a kinetochore?

Answer 11

Protein complex at the centromere where spindle fibers attach.

Question 12

What happens in Prophase?

Answer 12

Chromosomes condense; nuclear envelope begins to break down; centrosomes move to opposite poles.

Question 13

What happens in Prometaphase?

Answer 13

Nuclear envelope disappears; spindle fibers attach to kinetochores on sister chromatids.

Question 14

What happens in Metaphase?

Answer 14

Chromosomes line up in the middle of the cell (metaphase plate).

Question 15

What happens in Anaphase?

Answer 15

Sister chromatids separate and move toward opposite poles.

Question 16

What happens in Telophase?

Answer 16

Nuclear envelopes reform; chromosomes decondense; two new nuclei form.

Question 17

What is cytokinesis?

Answer 17

Division of cytoplasm — forms two separate daughter cells; cleavage furrow in animals, cell plate in plants.

Question 18

What does the G₁/S checkpoint monitor?

Answer 18

Cell size, nutrients, DNA damage, and external growth signals before DNA replication.

Question 19

What does the G₂/M checkpoint monitor?

Answer 19

Ensures DNA replication is complete and undamaged before mitosis.

Question 20

What does the spindle checkpoint monitor?

Answer 20

Ensures all chromosomes are properly attached to spindle fibers before anaphase begins.

Question 21

What are gametes?

Answer 21

Haploid (n) reproductive cells — sperm or eggs.

Question 22

What are somatic cells?

Answer 22

Diploid (2n) body cells — all cells except gametes.

Question 23

What is fertilization?

Answer 23

Fusion of two haploid gametes to form a diploid zygote.

Question 24

What are germ cells?

Answer 24

Cells that produce gametes via meiosis (sex cells).

Question 25

Define haploid vs. diploid.

Answer 25

Haploid (n) = 1 set of chromosomes; Diploid (2n) = 2 sets of chromosomes.

Question 26

What are homologous chromosomes?

Answer 26

Chromosomes with the same genes at the same loci, but possibly different alleles (one maternal, one paternal).

Question 27

What are sister chromatids?

Answer 27

Identical copies of a chromosome joined at a centromere, formed during S phase.

Question 28

How do homologous chromosomes differ from sister chromatids?

Answer 28

Homologs come from different parents; sister chromatids are identical copies of one chromosome.

Question 29

What happens in Meiosis I?

Answer 29

Homologous chromosomes separate → two haploid cells form.

Question 30

What happens in Meiosis II?

Answer 30

Sister chromatids separate → four unique haploid gametes form.

Question 31

What is crossing over and when does it occur?

Answer 31

Exchange of DNA between non-sister chromatids at chiasmata during Prophase I.

Question 32

What is independent assortment?

Answer 32

Random alignment of homologous chromosome pairs during Metaphase I → increases genetic variation.

Question 33

What is random fertilization?

Answer 33

Any sperm can fertilize any egg, adding even more genetic variation.

Question 34

How many divisions occur in mitosis vs meiosis?

Answer 34

Mitosis: 1 division → 2 identical diploid cells. Meiosis: 2 divisions → 4 unique haploid cells.

Question 35

Are daughter cells genetically identical in mitosis or meiosis?

Answer 35

Mitosis: identical; Meiosis: genetically unique.

Question 36

Does homologous pairing occur in both?

Answer 36

Only in Meiosis I (not in mitosis).

Question 37

What is a diploid-dominant life cycle?

Answer 37

Seen in animals — multicellular stage is diploid; gametes are haploid.

Question 38

What is a haploid-dominant life cycle?

Answer 38

Seen in fungi — multicellular stage is haploid.

Question 39

What is alternation of generations?

Answer 39

Plants and algae alternate between diploid sporophyte and haploid gametophyte stages.

Question 40

What is a deletion mutation?

Answer 40

A chromosome segment is missing.

Question 41

What is a duplication mutation?

Answer 41

A chromosome segment is copied twice.

Question 42

What is an inversion mutation?

Answer 42

A segment of a chromosome is reversed end-to-end.

Question 43

What is a translocation mutation?

Answer 43

A segment of one chromosome attaches to another chromosome (simple or reciprocal).

Question 44

What is euploidy?

Answer 44

Normal number of complete chromosome sets (e.g., human 2n = 46).

Question 45

What is polyploidy?

Answer 45

Having 3 or more complete chromosome sets (e.g., 3n, 4n; common in plants).

Question 46

What is aneuploidy?

Answer 46

Abnormal number of individual chromosomes (extra or missing).

Question 47

What causes aneuploidy?

Answer 47

Nondisjunction — chromosomes fail to separate during meiosis I or II.

Question 48

What is trisomy?

Answer 48

One extra chromosome (2n + 1); e.g., Down syndrome (Trisomy 21).

Question 49

What is monosomy?

Answer 49

One missing chromosome (2n − 1); e.g., Turner syndrome (XO).

Question 50

What is Trisomy 18 (example)?

Answer 50

Edward’s syndrome — individual has an extra copy of chromosome 18 (47, 18+).