Cilia - Meiosis & Gametogenesis
Study online at quizlet.com/_8xgzp
1.
2.
At what point does crossing over occur?
When do the centromeres divide?
When do female cells arrest?
Crossing over occurs in Meiosis I
Centromeres divide only once, in Meiosis II
Female cells arrest in Prophase I of Meiosis I
Atresia
Follicular Degeneration
-occurs at any developmental stage
-apoptosis of granular cells and autolysis of oocyte
3.
Comparison of male and female meiosis
in male 4 sperm produced at end of meiosis
in female one egg & 2 polar bodies formed at end of meiosis
meiosis II for women doesn't complete until fertilization (2nd polar body)
4.
Describe key parts of the male organ involved
in reproduction.
Seminiferous tubules: where spermatozoa are produced via meiosis
Epididymus: where the spermtazoa mature
In which tissues does meiosis occur? What
cells/structures involved?
5.
Describe processes of mitotic and meiotic
division that occur during spermatogenesis
Type A spermatogonia:
-some act as stem cells and divide to produce new stem cells that recycle
-others are progenitor cells that undergo 2-3 rounds mitosis (without cytokinesis,
to maintain the intercellular bridge) and differentiate into type B
Type B spermatogonia:
-undergo mitosis (without cytokinesis) to produce two diploid primary
spermatocytes (2n) which enter meiosis
Primary spermatocytes = meiosis I (23n, 46C)
Secondary spermatocytes = meiosis II (23n, 23C)
Spermatids → Mature spermatozoa + residual bodies = process of
differentiation/spermiogenesis (intercellular bridges lost)
NOTE: intracellular bridges are maintained during 1st and 2nd meiotic divisions
(otherwise would be missing a lot of genes if X was separated from Y)
6.
Describe the differences between mitosis and
meiosis
mitosis: cell division → 2 identical diploid daughter cells
meiosis: cell division → 4 haploid daughter cells (gametes) with half #
chromosomes
Meiosis has 2 unique events:
-genetic recombination
-chromosome # reduced to half
7.
Describe the different types of nuclear division that occur in
spermatogonia, spermatocytes and spermatids. MEMORIZE
SLIDE 16/38
1. Spermatogonia (2n, 2C) (46 chromosomes, 46 sis chromatids)
# chromosomes and chromatids present in cells during each
stage of spermatogenesis
2. Primary spermatocytes (2n, 4C) (46 chromosomes, 92 sis
chromatids)
(mitotic differentiation occurs)
(1st meiotic division occurs)
3. Secondary spermatocytes (n, 4C) (23 chromosomes, 46 sis
chromatids)
(2nd meiotic division occurs)
4. Spermatids (n, 2C) (23 chromosomes, 23 sis chromatids)
(differentiation occurs)
5. Spermatozoa (n, 2C) (23 chromosomes, 23 sis chromatids)
8.
Describe the different types of nuclear division that occur in
the development of oogonia, oocytes and zygote
Primordial follicles (2n, 2C) (46 chromosomes, 46 sis
chromatids)
-flattened follicular cells (corona radiata)
Primary follicles (46 chromosomes, 92 sis chromatids)
-single layer of granulosa cells around the primary oocyte
-zona pellucida (glycoprotein layer) betwen granulosa cells and
oocyte
(first meiotic division causes extrusion of first polar body with
half the chromosomes and formation of secondary follicle with
the other half)
Secondary follicles (23 chromosomes, 46 sis chromatids)
-cells from granulosa layer produce fluid to produce large, fluidfilled antral cavity
-fibroblastic cells outside follicles develop into steroid-secreting
theca interna and theca externa
Antral follicle
-antrum increases in size until it pushes the secondary oocyte
out in ovulation (only one oocyte per 28 days makes it to this
stage)
9.
Describe the events occurring during each stage of the meiotic
division
1. Chromosome replication
-unpaired chromosomes replicate (you know have X shape and
sister chromatids)
-still have same # of unique homologous chromosomes (46 in
human)
2. Meiosis I (reductional division)
-pairing and segregation of chromosomes
-chromosomes # divides by 2 (2n → n) [dip → haploid]
-sister chromatid # divides by 2 (4C → 2C) in Anaphase I
3. Meiosis II (equational division)
-chromosome # stays the same (n → n) [haploid]
-sister chromatid # divides by 2 (2C → C) in Anaphase II
10.
Describe the events that occur during the two
phases of female meiosis
1. Embryonic Phase
2. Postnatal Phase
1. Embryonic Phase
-primordial germ cell produced outside of gonad and migrates in
-primordial germ cells enter Prophase I (primary oocytes)
-arrested in Diplotene phase of Prophase I until puberty
2. Postnatal Phase
-primary oocytes quiescent until puberty
-follicular development at puberty
-completion of first meiotic division
-ovulation after puberty
11.
Describe the process involved in the first
cleavage division of the zygote
4-6 hours after fusion of gametes, 2 sets of haploid chromosomes each get
surrounded by distinct membranes to form the pronuclei
each pronucleus moves from its subcortical position to a more central position
8-12 hrs after fertilization, DNA in each pronucleus duplicates (a round of DNA
synthesis) such that each haploid set of chromosomes has 2 sister chromatids and
can complete mitosis 2n, 2c → 2n, 4c
pronuclear membrane breaks down, metaphase spindle forms and chromosomes
lie at metaphase plate
anaphase and telophase are completed and clevage furrow forms
two-cell embryo is formed
12.
Describe the sequence of events that occur
during the fertilization of human eggs
(structures and mechanisms)
a capacitated spermatazoa travels to the isthmus (upper part) of the fallopian tube
and attaches to the sperm receptor ZP3 on the ovum surface of the zona pellucida
Acrosome reaction: acrosin enzyme released and digests through the zona
pellucida and fuses with the egg membrane
Cortical Granule Reaction: cortical granules from egg release their contents into
the perivitelline space, changing resting membrane potential of the oocyte plasma
membrane
1. Second meiotic division and second polar body extrusion (with half of the sister
chromatids)
2. Membrane depolarization inhibits penetration of other sperm (block to
polyspermy). The enzymes secreted by cortical granules hydrolyze ZP3 molecules
(Zona reaction)
13.
DRAW MEIOSIS VS MITOSIS
see bookmark "meiosis v. mitosis"
14.
How do Leydig cells assist in meiosis?
produce testosterone in the presence of lutenizing hormone stimulation
present adjacent to (outside) seminiferous tubules
Have mitochondria tubular crisate, abundant SER and a well-developed Golgi App
-if something goes wrong with the Leydig cells → testosterone not produced →
spermatogenesis impaired → mature sperm not released from sertoli cells →
infertility
15.
How do Sertoli cells assist in
meiosis?
Sertoli cells form tight junctions (blood-testis barrier) with the seminiferous epithelial to divide it into
two parts:
-Basal (containing spermatogonia, site of mitosis)
-Adluminal (containing primary spermatocytes (first meiotic division), secondary spermatocytes (2nd
meiotic division), early spermatids and late spermatids (differentiation))
Sertoli cells also secrete hormones, testicular fluid and proteins required for spermatogenesis
they also phagocytose the cytoplasm shed during spermiogenesis
DO NOT DIVIDE IN TESTIS
16.
Spermiation
Spermiation (release of sperm from epithelial into lumen of seminiferous tubule)
The newly formed spermatozoa are immotile and incapable of fertilization until they enter the female
reproductive system and become capacitated
17.
Spermiogenesis: 4 phases of
Spermatid Maturation
Golgi: hydrolytic enzymes in small vesicles form acrosomal vesicle. Centrioles leave the nucleus,
beginning to form microtubules
Cap: acrosomal vesicles increase in size (now called acrosome), partly surround the nucleus
Acrosomal: Nucleus more condensed and volume reduced
Maturation: shedding of much cytoplasm as residual bodies, elongation of spermatids
18.
Stages of Meiotic Prophase I
Profanely, Led Zeppelin Punished Dirty Divas
Prophase I:
Leptotene: long & thin chromosomes, no pairing, no sister chromatids (SC)
Zygotene: axial/lateral elements of SCs form, homologous pairing, recombination (conjugation)
Pachytene: full extent of SCs and homolog pairing, chromosomes shorter and thicker
Diplotene: SC disappears, homologs repel, chiasmata visible
Diakinesis: separation of the homologous chromosomes to opposite poles
19.
20.
What are chiasmata?
crossing-over between non-sister chromatids of paired homologous chromosomes
What is a synaptonemal
complex?
proteinaceous structures uniting homologous chromosomes during zygotene stage of Prophase 1
zygotene: when sperm and oocyte join during fertilization
21.
What is a zygote?
a zygote is formed immediately after fertilization, so when a sperm and an oocyte fuse they become a
diploid cell
22.
What is the difference between a chromatid and a
chromosome? What do haploid, diploid, triploid
and tetrad mean?
2 sister chromatids (attached at centrosome) = 1 chromosome
1 homologous pair = 2 chromosomes with same gene locations side by side
(eg. when chromosomes replicated)
4 chromatids = 2 homologous chromosomes = 1 tetrad
haploid: 1 set of unpaired chromosomes (eg. 23)
diploid: paired chromosomes (eg. 46 in somatic cells)
triploid: 3n chromosomes (eg. 69)
23.
what is the syncytium
multinucleated cell formed by fusing cells. This happens in spermatogenesis
when spermatogonia undergo mitosis without the last step of cytokinesis to
preserve the intracellular bridge.
This bridge allows haploid cells to share their intracellular contents to help
everyone undergo meiosis at the same time
normal, mature sperm will have one X or one Y chromosome
X & Y chromosomes differ greatly in size and gene content
24.
When does DNA synthesis occur?
Before the the Meiosis I but not before Meiosis II
Before mitosis