Chapter II: Meiosis

Question 0

Crossing over

Answer 0

Physical exchange of chromosomal material between non sister chromatids

Question 1

Meiosis

Answer 1

Type of cell division that produces genetic variability, reduces ploidy (2n -> n), and produces 4 gametes
Consists of 2 divisions: Reductional (Meiosis I) and Equational (Meiosis II)

Question 2

Synapsis

Answer 2

The pairing of homologous chromosomes

Question 3

Bivalents (Tetrads)

Answer 3

Synapsed homologs (homologous chromosomes) during prophase I

Question 4

Dyads

Answer 4

Product of the separation/disjunction of bivalents

Contains 2 sister chromatids joined at the centromere

Question 5

Monads

Answer 5

Product of separation of dyads

Forms 4 haploid cells

Question 8

Prophase I

Answer 8

Same as mitosis:

• chromosomes condense
• centrioles split and spindle fibers form
• nuclear membrane dissolves

Question 9

Five stages of Prophase I

Answer 9

1. Leptonema (Leptotene)
2. Zygonema (Zygotene)
3. Pachynema (Pachytene)
4. Diplonema (Diplotene)
5. Diakinesis

Question 10

Leptonema (Leptotene)

Answer 10

Replicated chromatids condense

chromosomes and chromomeres become visible

Question 11

Zygonema (Zygotene)

Answer 11

Synapsis occurs

Synapsed pairs of homologs are called bivalents

Question 12

Pachynema (Pachytene)

Answer 12

Synapsis is completed
Nuclear membrane starts to dissolve
Crossing over can occur (between non sister chromatids)

Question 13

Diplonema (Diplotene)

Answer 13

the bivalent consists of 2 pairs of sister chromatids
Condensation continues and crossing over finishes causing the observance of chiasmata (a point where non sister chromatids cross over)

Question 14

Diakinesis

Answer 14

Terminalization of chiasmata
Breakdown of nucleolus and nuclear membrane
Spindle fiber forms and attaches to centromeres

Question 15

Metaphase I

Answer 15

Bivalents line up along the equatorial plane and alignment is independent and random (independent assortment)

Question 16

Anaphase I

Answer 16

Spindle fibers reel the bivalents to opposite poles, separating them in the process forming dyads. (Random seg)

Question 17

Telophase I

Answer 17

• Decondensation of chromosomes, and reformation of nuclear membrane occurs around dyads
• Daughters cells are haploid
• Cytokinesis occurs

Question 18

Prophase II

Answer 18

• condensation of chromosomes
• dissolution of nuclear membrane
• formation do spindle fibers

Question 19

Metaphase II

Answer 19

Dyads line up along the equatorial plane

Question 20

Anaphase II

Answer 20

Late replication of centromeres, and depolymerization of spindle fibers reels the dyads to opposite poles, separating them and forming monads.

Question 21

Telophase II

Answer 21

Decondensation of monads occur
Nuclear membrane reforms
Produces 4 haploid cells

Question 23

Equational Division (Meiosis II)

Answer 23

Ploidy of starting cell is equal to the ploidy of daughter cell because centromeres weren’t halved (n->n)
Dyads splits into 2 monads of one chromosome each, producing 4 haploid cells

Question 26

Reductional Division (Meiosis I)

Answer 26

Starts with S phase
Chromosomes are reduced by one half; diploids are reduced to haploids (2n->n)
Bivalents separate, yielding 2 dyads