Meiosis from Rich Notes

Question 1

How many pairs of autosomes do humans have? How many pairs of sex chromosomes do humans have? What types of sex chromosomes do females have? Males? (Normally)

Answer 1

22; 1; XX; XY

Question 2

What are two ways in which meiosis creates genetic diversity?

Answer 2

random assortment of chromosomes and recombination

Question 3

What letter is used to designate the number of haploid sets of chromosomes in a cell? What letter is used to designate the content of DNA in a cell?

Answer 3

N; C

Question 4

How much DNA content do each of the following have? 
A diploid somatic cell in G1
A diploid somatic cell  in G2
A gamete in prophase of meiosis
Gametes after Meiosis I? II?

Answer 4

2C
4C (finished DNA replication in S phase)
4C
2C
1C

Question 5

How many sets of haploid chromosomes do each of the following have?
gamete after Meiosis I
gamete after Meiosis II

Answer 5

1N

1N

Question 6

What is the term for when a cell has an abnormal number of chromosomes that are not complete haploid sets? What is it called when an extra copy of a single chromosome is present? What is it called when there is a loss of one copy of a single chromosome?

Answer 6

aneuploid; trisomy; monosomy

Question 7

Where do close pairing and recombination take place?

Answer 7

synaptonemal comlex

Question 8

What is the process that takes place in the synaptonemal complex? (Something binds, then something binds, etc.)

Answer 8

proteins deposited on long axis of chromosome forming axial elements, DNA extends in loops, other proteins deposited in between axial ele., axial ele. now become lateral ele., lateral ele. connected by transverse filaments, these overlap to form central element

Question 9

What is located at intervals along the synaptonemal complex? They contain enzymes that mediate the recombination between non-sister chromatids of homologous chromosomes.

Answer 9

recombination nodules

Question 10

What are the steps of recombination?

Answer 10

Spo11 makes ds break in 1 chromatidof 1 of the paired homologs, end of DNA digested in 5’ to 3’ direction by nuclease, tail invades adjacent chromatid of other paired homolog, break in DNA repaired by new DNA synthesis using homologous chromatid as template- forms crossover, resolvase releases the crossover, few crossovers remain as chiasmata until separation; ready to separate at anaphase

Question 11

What are the stages of Meiotic Prophase I?

Answer 11

Leptotene, Zygotene, Pachytene, Diplotene, and Diakenesis

Leprous Zebras Pack Diplomatic Diaries.

Dumb, but it works.

Question 12

During which stage of prophase Ido the chromosomes condense, homologous chromosomes begin to pair, and axial elements of the synaptonemal complex form?

Answer 12

leptotene

Question 13

During what stage of Prophase I do the synapsis of chromosomes begins and the central and lateral elements of the synaptonemal complex begin to form?

Answer 13

zygotene

Question 14

During which stage of Prophase I is synapsis and recombination both complete?

Answer 14

pachytene

Question 15

During what stage of Prophase I does the synaptonemal complex disassemble and oocytes become arrested until stimulated by ovulation? (fun stuff)

Answer 15

diplotene

Question 16

During which stage of Prophase I are the chromosomes fully condensed and ready for metaphase? This stage is homologous to prometaphase in mitosis.

Answer 16

diakenesis

Question 17

What aligns on the metaphase plate in Metaphase I?

Answer 17

homologous chromosomes

Question 18

What are attached to the same spindle pole in Metaphase I?

Answer 18

both sister chromatids of the same chromosome

Question 19

During metaphase I, what holds the homologs together, and what holds the sister chromatids on a chromosome together?

Answer 19

chiasmata; cohesin at the centromere

Question 20

What separates in anaphase I? What else happens?

Answer 20

homologous chromosomes; remaining cohesin along arms is removed, chiasmata disassembled

Question 21

What does NOT occur in telophase I and cytokinesis of meiosis, which is different than what occurs in telophase of mitosis? Why?

Answer 21

the nuclear envelope does not reform and the chromosomes do not decondense; MPF activity remains high

Question 22

What phases are basically skipped between end of Meiosis I and start of Meiosis II?

Answer 22

interphase and prophase II

Question 23

Do the daughter gametes from Meiosis I undergo DNA replication before they enter Meiosis II?

Answer 23

No.

Question 24

What attaches to opposite poles of the spindle during metaphase II?

Answer 24

kinetochores of sister chromatids

Question 25

What causes the release of sister chromatids during anaphase II?

Answer 25

separase

Question 26

What keeps the oocyte arrested at the diplotene stage?

Answer 26

MPF activity (it’s high due to high cyclin B)

Question 27

What helps keep Cyclin B levels high to keep MPF levels high to keep the oocyte arrested in the diplotene stage?

Answer 27

increased synthesis and prevention of degradation of Cyclin B; involves c-Mos (kinase, part of cytostatic factor) and members of MAP kinase pathway

Question 28

When the oocyte is stimuated to enter metaphase I, MPF activity declines to allow the events of metaphase I, anaphase I, and telophase I to take place. MPF activity increases again and arrests the oocyte at metaphase II until what occurs?

Answer 28

fertilization (really fun stuff)

Question 29

Compare and contrast the number of cell divisions and progeny of mitosis and meiosis. What else does meiosis have that mitosis doesn’t? (Think of the phases)

Answer 29

Mitosis has 1 cell division, 2 diploid but genetically identical progeny
Meiosis has 2 cell divisions, 4 haploid but genetically diverse progeny;
an extended prophase with recombination and chromosome pairing and segregation

Question 30

How many copies of the chromosomes do gametes have? What is this condition called? When two gametes fuse, what is this condition called?

Answer 30

one; haploid; diploid