W3 Meiosis

Question 1

Spermatogenesis:

Answer 1

1) Spermatogonium (2N)
2) Primary spermatocyte (2N)
3) Secondary spermatocytes (Meiotic division 1)
4) Spermatids (N) (Meiotic division 2)
5) Spermatozoa (Differentiation)

Question 2

Oogenesis:

Answer 2

1) Oogonium (2N)
2) Primary oocyte (2N)
3) Secondary oocyte, First polar body (Meiotic Division 1)
4) Ootid (N), Second polar body (N), Polar bodies (N) (Meiotic division 2)
5) Ovum (N) (Differentiation)

Question 3

Meiosis in plants:

Answer 3

-Gametophyte (n) stage: haploid cell-organism, gametes are produced
-Sporophyte (2n) stage: haploid spores produced by meiosis

Question 4

Meiosis overview:

Answer 4

Meiosis 1: Reductional division. Homologous chromosomes pair, exchange parts (recombine) and segregate.
-Prophase 1 (Leptotene, Zygotene, Pachytene, Dplotene, Diakinesis)
-Metaphase 1
-Anaphase 1
-Telophase 1
Meiosis 2: Equational division. Sister chromatids separate to produce haploid gametes
-Prophase 2
-Metaphase 2
-Anaphase 2
-Telophase 2
Cytokinesis: Cytoplasm divides, forming new haploid cells

Question 5

Prophase 1: Leptotene

Answer 5

-Chromatids begin to thicken but are not yet visible as separate entities
-Centrioles move apart

Question 6

Prophase 1: Zygotene

Answer 6

-Synapsis occurs: Zipping together of homologous chromosomes
-The zipper is an elaborate protein structure called the synaptonemal complex
-Chromosomes form a bivalent, or tetrad (4 strings of DNA)

Question 7

Prophase 1: Pachytene

Answer 7

-Full synapsis of homologues
-Recombination Nodules appear
-Crossing over: genetic exchange between non-sister chromatids of a homologous pair

Question 8

Prophase 1: Diplotene

Answer 8

-Synaptonemal complex dissolves, chromosomes keep condensing
-Homologous chromosomes start to move apart but remain tightly joined at chiasmata - sites where crossing over occured
-Meiotic arrest occurs in many species

Question 9

Prophase 1: Diakinesis

Answer 9

-Further condensation of chromatids
-4 chromatids of bivalent clearly visible
-Chiasmata still visible
-Nuclear envelope breaks down adn microtubules of the spindle apparatus begin to form

Question 10

Metaphase 1:

Answer 10

-Bivalents align randomly at the metaphase plate
-Homologous chromosomes are still attached at the chiasmata
-Kinetochores of sister chromatids in one homolog attach to spindle microtubules from one pole, while those of the other homolog attach to the opposite pole

Question 11

Anaphase 1:

Answer 11

-Chiasmata dissolve to allow homologous chromosomes to move towards opposite poles
-Unlike mitosis, it is the homologous chromosomes not sister chromatids that separate (centromeres do not divide)
-Each pole receives a haploid set (n) of replicated chromosomes

Question 12

Telophase 1 and Interkinesis:

Answer 12

-Nuclear membranes form around chromosomes
-Followed by cytokinesis and interkinesis (no DNA replication)

Question 13

Prophase 2:

Answer 13

-Chromosomes condense (if they decondensed in interkinesis)
-Centrioles move towards poles
-Nuclear envelope breaks down

Question 14

Metaphase 2:

Answer 14

-Chromosomes align at metaphase plate
-Kinetochores of sister chromatids attach to microtubules
-Two features distinguish metaphase 2 from mitotic metaphase:
-Number of chromosomes is half that in mitotic metaphase in same species
-Sister chromatids are no longer identical due to crossing over in meiosis 1

Question 15

Anaphase 2:

Answer 15

-Centromeres split and sister chromatids move to opposite poles

Question 16

Telophase 2 to cytokinesis:

Answer 16

-Membranes form around each of 4 daughter nuclei
-Cytokinesis places each nucleus in a separate cell, resulting in 4 haploid gametes

Question 17

Meiosis in lily anthers - Complete

Question 18

Consequences of non-disjunction (failure to separate)

Answer 18

Non-disjunction in anaphase 1: All resulting gametes are abnormal
-Zygotes will be aneuploid (have one more or less than the normal chromosome content)
Non-disjunction in anaphase 2: Half ofresulting gametes will be normal