Lecture 5 - Reproduction Flashcards
1
Q
Define Asexual Reproduction
A
A single individual is the sole parent and passes copies of all its genes to its offspring
- 1 parent
- clone offspring
2
Q
Define Sexual Reproduction
A
Two parents give rise to offspring that have unique combinations of genes inherited from each parent
3
Q
Advantage of asexual reproduction
A
Energetically cheaper
- no time/energy wasted on finding a mate (courtship rituals, etc)
- every member of the population can yield offspring
4
Q
Animals that asexually reproduce
A
- not mobile or live in sparse populations
- cannot search for or find a mate - in constant environments
- genetic diversity is less important for reproductive success
- few pressures on them, their “plan works”
* rare
5
Q
Type of Asexual Reproduction
A
- Budding
- Regeneration
- Parthenogenesis
6
Q
Budding
A
Asexual
- small offspring buds from larger parents
- bud grows by mitotic cell division and differentiates before bud breaks away
7
Q
Regeneration
A
Asexual
- replacement of damaged or lost limbs, or entire individual
- example starfish cut into pieces will regenerate as many starfish as pieces
8
Q
Parthenogenesis
A
Asexual
- development of an unfertilized egg into a new individual
- only practiced by females - species also often practice sexual reproduction
ex: bees: fertilized eggs develop into females, unfertilized into males
9
Q
Advantages and disadvantage of sexual reproduction
A
Adv: provides genetic diversity
Disadv: Is energetically more expensive *but 99.9% of eukaryotes do it… so seems to work
10
Q
General Process of Sexual Reproduction
A
- Gametogenesis
- making haploid cells or gametes
- meiotic cell division - Spawning/mating
- bringing gametes together - Fertilization
- union of sperm and egg to produce a diploid zygote with two sets of chromosomes, one from each parent
11
Q
Gametogenesis
A
Produces: gametes
- eggs - non-motile
- sperm - move by flagella
Occurs: gonads
- female ovaries
- male testes
Process:
- diploid (2 sets of each chromosome) to haploid (only one set of each)
12
Q
Germ Cells
A
- precursors to gametes
- diploid
- small collection of cells in early mammalian embryo are induced to become primary germ cells through signals from their neighbors
- develop differently from somatic cells of rest of the body
- proliferate and migrate to developing gonads
- signaled to develop into sperm or eggs depending on whether gonads have started developing into testes or ovaries
* not based on the chromosomes they have themselves
*Single gene on Y chromosome (SRY) important for dictating gonad development into testes
13
Q
How do germ cells develop into sperm or eggs?
A
- signaled by the developing gonads, whether male or female
*not based on their sex chromosomes
14
Q
Spermatogenesis (steps)
A
- after germ cells have taken up residence in testes
- TIME: begins at puberty
1. Germ Cells (until puberty) - mitosis - differentiate, proliferate
2. Spermatogonia - mitosis - differentiate
- some on track to become sperm, others just divide over and over
3. Primary Spermatocytes (1 diploid)
*meiosis I*
- Spermatids (2 haploid - connected by cytomplasmic bridges)
*meiosis II*
- More spermatids (4 haploids - cytoplasmic bridgeS)
- mature - Sperm (4 haploid)
15
Q
Spermatogenesis: Where, when, how long?
A
- seminiferous tubules tightly coiled within each testes (move from the outside in)
- after puberty, continuous
- ~ 65 days
16
Q
Oogenesis (Part I)
(where, when, how)
A
During embryonic development
in the ovaries
- Germ cells
(mitosis)
- oogonium
(mitosis)
- oocytes
(meiosis)
- Stop at prophase I
* at this point all primary oocytes are present
17
Q
Ovarian Cycle
A
- all primary oocytes are present in embryo at birth
- When Oogenesis resumes
- involveds ovulation and corpus luteum development
18
Q
Primary Oocyte
A
- each primary oocyte is surrounded by layer of cells that form a follicle
- begin puberty and menopause 6-12 mature each month
- others remain paused
- oocyte and rest of follicle will grow
- after about 1 week 1 will be larger than the others (out of the 6-12)
- the big one will continue to mature, others degenerate
- just before ovulation primary oocyte will finally undergo meiosis
19
Q
How manny primary oocytes develop each month?
A
- 6-12 from puberty to menopause
- only 1 actually matures all the way, others degenerate
20
Q
Oogenesis (Part II)
A
- Primary oocyte undergoes mitosis very close to the edge of the cell
- 1 daughter cell gets almost all cytoplasm (secondary oocyte), other gets very little (first polar body) - secondary oocyte divides in meiosis, forms one large OOTID), other is a second pilary body
- ootid develops into ovum
*primary oocyte
* secondary oocyte
* first polar body
*secondary polar body
*ootid
* ovum
21
Q
Result of Oogensis
A
- 1 mature haploid egg per primary oocyte
- 1 mature egg per month
* mature means it is through metaphase II
22
Q
When does the egg complete its cell division?
A
- does not complete until fertilization occurs
- when expelled from ovary, it is arrested in metaphase of meiosis II
23
Q
Oogenesis vs spermatogenesis
A
Oogensis
- initiated once in a finite population of cells
- one gamete produced per meiosis
- completion of meiosis delayed for months or years
- meiosis arrested at first meiotic prophase and reinitiated in a smaller population fo cells
- diff of gamete occurs with diploid, in first meiotic prophase
Spermatogenesis
- meiposis initiated continuously in a mitotically dividing stem cell pop
- four gametes produced per meiosis
- meiosis completed in days or weeks
- meiosis and differentiation proceed continuously without cycle arrest
- diff of gametes occurs while haplois, after meiosis ends
24
Q
Ovulation
A
- after 2 weeks of follicular growth, follicle ruptures and releases egg
- follicle cells that remain in the ovary continue to proliferate and form a mass of tissue about the size of a marble
- corpus luteum aka yellow body develops
25
Corpus Luteum
- important in ovulation
- functions as an endocrine gland producing estrogen and progesterone for about 2 weeks
- degenerates unless pregnancy occurs
26
Implantatoin
- egg release into body cavity cloe to openings of oviducts (fallopian tubes)
- egg drawn into oviduct
- where fertilization takes place
- first few divisions in oviduct
- moves down oviduct to uterus, attaches to epithelial lining
- implantation in endometrium of uterus
27
Hormones Leading up to Ovulation
1. puberty: hypothalamus increases releas eof gonatrophin releasing hormone (GnRH)
2. anterior piruitary secretes 2 tropic hormones
- FSH - follicle stimulating hormone
- LH - leutenizing hormone
3. FSH and LH trigger small sets of primary oocytes to mature in ovaries
- follicles of oocytes steadily increase estrogen
4. Estrogen
- initially negative feedback on FSH and LH - keeps in check
- ~ day 12, switches to positive feedback
- surge of LH (and some FSH) occurs
- triggers ovulation: follicole ruptures and releases egg and develops in to CL
28
Hormones after ovulation
- spike of LH has just cuase ovulation
- LH and FSH levels are high, estrogen low
1. corpus luteum
- secretes progesterone (and some estrogen)
- controls growth and maintenance of endometrium
- inhibits GnRH, LH, FSH release (prevents new follicles from maturing)
2. If egg not fertilized
- CL disintigrates
- GnRH, FSH, LH all increase - hypothalamus and pituitary relased from negative feedback
- cycle begins again
29
Increased GnRH leads to...
Increased FSH and LH
30
Follicle development and increased estrogen leads to..
- decreased FSH and LH
- THEN increased FSH and LH
31
LH surge leads to...
ovulation
32
Increased progesterone leads to...
- endometrium dev
- decreased GnRH, FSH, LH
33
Corpus luteum degenerates..
- decreased progesterone
- increased GnRH, FSH, LH
34
Female Hormone Cycle
35
Fertilization results in a...
zygote
36
Events in fertilization:
1. Sperm and egg recognize eachother
2. sperm is activated, enabling it to gain access to egg's plasma membrane
3. Plasma membrane of egg fuses with plasma membrane of single sperm
4. egg blocks entry of all additional sperm
5. egg is metabolically activated and stimulated to start development
6. egg and sperm nuclei fuse to create the diploid nucleus of the zygote
37
Sperm - Egg recognition
- specific molecules mediate interactions
- direct sperm towards egg
- prevent fertilization of eggs by sperm of other species
- eggs release chemical attractant that increase motility of sperm and cause them to swim toward egg
38
Layers of the Egg
- sperm must successfully penetrate protective layers of egg
Two layers:
1. Thick Jelly coat
2. Protein Envelope
\* callad "Zona Pellucida" in humans
THEN sperm can access plasma membrane of egg
39
Acrosome
- Membrane enclosed cap at front of sperm head
- contain enzymes for digesting protective layers as well as actin and other proteins to help sperm contact egg plasma
40
Sperm Activation
1. sperm penetrates jelly coat
2. acrosome binds to specific receptors in Zona Pellucida
3. Binding to Zona Pellucida triggers \*acrosomal reactoin\*
4. acrosomal enzymes are released
5. digest a hole through zona pellucida
6. create a pathway for sperm to get to the plasma membrane of the ovum
41
Fusion
Allowed by acrosomal pathway
- sperm reaches ovum, egg and sperm membranes are fused
- sperm nucleus brough into egg cytoplasm
42
Blocks to Polyspermy
- mechanisms that prevent more than one sperm from entering egg
FAST:
- influx of Na+ cations hanges charge difference across membrane (rapid depolarization)
- transiently prevents other sperm from binding to plasma membrane
SECONDARY:
- sperm entry tino egg stimulates local release of Ca++ from stroes in the ER into the cytoplasm
- this spreads in a wave
- causes \*cortical granules\* that are stored underneath the plasma membrane to fuse with the plasma membrane and release contents
- protein envelope is converte into a physical barrier that sperm cannot penetrate
43
Cortical Reaction
\*protein envelope is converted to a physical barrier that sperm cannot penetrate
- influx of Ca++ causes relase of cortical granules
1. causes fertilization envelope (zona pellucisa) to harden
2. degrade sperm binding molecules on surface of envelope
(sometimes. ..)
3. protein envelope rises to form a fertilization envelope (NOT in mammals)
44
Fusion of Sperm and egg nuclei
- two halpoid nuclei must combine chromosomes into one dilpoid nuleus
- in mammals, nuclear membranes do not fuse directly together
- approach each other but remain distinct until membrane of each nucleus has broken down in preparation for sygote's first mitotic division
