Chapter 2: Reproduction Flashcards
diploid (2n)
Autosomal cells
Contain 2 copies of each chromosome
46 in humans
haploid (n)
Germ cells
Contain 1 copy of each chromosome
23 in humans
cell cycle
The cycle in which eukaryotic cells replicate
Specific series of phases during which a cell grows, synthesizes DNA, and divides
Derangements may lead to unchecked cell division and cancer
Consists of 4 stages: G1–>S–>G2–>M
Cells that do not divide spend their time in G0
***CELLS UNDERGO FINITE NUMBER OF DIVISIONS BEFORE PROGRAMMED DEATH
interphase
First three stages of cell cycle (G1, S, and G2)
Individual chromosomes are not visible with light microscopy, but in condensed chromatin form
DNA must be available to RNA polymerase so genes can be transcribed
G0 stage
Offshoot of G1 phase
Cell is not preparing for division, but simply living
chromatin
Less condensed form that individual chromosomes take during interphase
DNA must be available to RNA polymerase so genes can be transcribed
G1 stage
Presynthetic gap
Cells create organelles for energy and protein production while increasing their size
Passage into S stage governed by restriction point
Main protein in charge of this is p53
restriction point
passage into S stage from G1 stage governed by certain criteria, such as proper complement of DNA
S stage
Synthesis of DNA
Cell replicates genetic material so each daughter cell will have identical copies
After replication each chromosome consists of 2 chromatids bound together at centromere
Cells entering G2 have twice as much DNA as the cells in G1
Humans in S stage have 46 chromosomes even though 92 chromatids are present
G2 stage
Postsynthetic Gap
Cell passes through another quality control checkpoint to ensure there are enough organelles and cytoplasm for two daughter cells and checks for errors
Checkpoint also moderated by p53
M stage
Mitosis + Cytokinesis
Mitosis: prophase, metaphase, anaphase, and telophase
Cytokinesis: splitting of cytoplasm and organelles into daughter cells
cyclin-dependent kinases (CDK’s)
Molecules responsible for the cell cycle (along with cyclins)
CDK’s require presence of right cyclins
Concentrations of various cyclins increase and decrease during specific stages, which bind to CDK’s, creating activated CDK-activated complex
This complex can then phosphorylate transcription factors
transcription factors
promote transcription of genes required for the next stage of the cell cycle after it’s phosphorylated by CDK-cyclin complexes
mitosis
Process by which 2 identical daughter cells are created from a single cell
One round of replication, one round of division
2 stages: prophase, metaphase, anaphase, telophase
Occurs in somatic cells (not involved in sexual reproduction)
somatic cells
Not involved in sexual reproduction
Divide by mitosis
prophase
First stage in mitosis
KEY CONCEPTS: CHROMOSOMES CONDENSE, SPINDLE FORMS
1. Condense chromatin into chromosomes, centriole pairs separate and move towards opposite poles of cells (responsible for correct division of DNA)
2. Centrioles begin to form spindle fibers, which are made of microtubles
3. Nuclear membrane dissolves, kinetochores appear
4. Nucleoli become less distinct
2n (2 chromosomes–4 sister chromatids paired)
kinetochore
Protein structures located on the centromeres that serve as attachment points for specific fibers of the spindle apparatus called kinetochore fibers
Appear at the centromere during prophase
metaphase
Second stage in mitosis
KEY CONCEPTS: CHROMOSOMES ALIGN
1. Centriole pairs are now at opposite ends of cell, and kinetochore fibers interact with TWO fibers of spindle apparatus to align the chromosomes at the metaphase plate, which is equidistant between the two poles of the cell
2n (2 copies of chromosome, 4 chromatids paired)
kinetochore fibers
Specific fibers of the of the spindle apparatus that attach at the kinetochore during prophase
Align the chromosomes at the metaphase plate during metaphase
Pull sister chromatids apart during anaphase
anaphase
Third stage in mitosis
KEY CONCEPTS: SISTER CHROMATIDS SEPARATE
Centromeres split so each chromatid has its own distinct centromere, thus allowing sister centromeres to separate
4n (4 copies of chromosome)
telophase
Fourth stage in mitosis
KEY CONCEPTS: NEW NUCLEAR MEMBRANES FORM
Essentially a reverse of prophase
1. Spindle apparatus disappears
2. Nuclear membrane reforms around each set of chromosomes, nucleoli reappear
3. Chromosomes uncoil, resuming interphase form
4n (4 copies of chromosome)
cytokinesis
separation of cytoplasm and organelles so each daughter cell has supplies to survive on its own
meiosis
Occurs in gametocytes (germ cells) and results in up to 4 nonidentical sex cells (gametes)
One round of replication followed by 2 rounds of division
Number of chromosomes is halved; each daughter cell has 23 chromosomes
Occurs only in sex cells
meiosis I
Homologous chromosomes being separated, generating haploid daughter cells
AKA reductional division
2n–>n
meiosis II
Similar to mitosis
Separation of sister chromatids
AKA equational division
homologous pairs
23 in total in human genome
Each contains one chromosome inherited from each parent
15 maternal and 15 paternal
Similar but not identical
After S phase, 92 chromatids organized into 46 chromosomes
sister chromatids
identical strands of DNA connected at the centromere
prophase I
First stage of meiosis
- Chromatin condenses into chromosomes
- Spindle apparatus forms
- Nucleoli and nuclear membrane disappear
- Homologous chromosomes come together and intertwine in synapsis, resulting in crossing over
centromere
Holds two chromatids together Contain kinetochores (attachment point for spindle fibers)
synapsis
Occurs during prophase I; homologous chromosomes come together and form a tetrad
May break at point of synapsis (chiasma) and cross over, exchanging pieces of DNA
chiasma
Point of synapsis and crossing over
genetic recombination
When chromosomes exchange pieces of DNA during crossing over
Increases variety of genetic combinations that can be produced via gametogenesis if unlinks linked genes
Linkage: tendency for genes to be inherited together
Mendel’s second law (of independent assortment)
States that inheritance of one allele has no effect on the likelihood of inheriting certain alleles for other genes
metaphase I
- Tetrads align at metaphase plate and each pair is attached to ONE spindle fiber by its kinetochore
anaphase I
Homologous pairs separate and are pulled to opposite poles (disjunction and segregation)
disjunction
Occurs during anaphase I
Homologous pairs are disjointed (from tetrad); maternal chromosome goes one way, paternal goes the other
Accounts for Mendel’s first law (of segregation)
Mendel’s first law (of segregation)
Caused by disjunction
Each paternal chromosome is separated from maternal chromosome and either chromosome can end up in either daughter cell
telophase I
Nuclear membrane forms around each new nucleus
Each chromosome still consists of two sister chromatids
Cell is now haploid
mitosis II
Similar to mitosis
Sister chromatids, as opposed to homologues, are separated from each other
No change in ploidy; haploid to start, haploid to finish (n–>n)
prophase II
Nuclear envelope dissolves
Nucleoli disappear
Centrioles migrate to opposite poles
Spindle apparatus begins to form
metaphase II
Chromosomes line up on metaphase plate
anaphase II
Centromeres divide, separating chromosomes into two sister chromatids Spindle fibers (2) attach to kinetochores and begin to pull apart sister chromatids from each other to opposite poles
telophase II
Nuclear membrane forms around each new nucleus
Cytokinesis follows
Up to four haploid daughter cells produced
sex
Determined by 23rd pair of chromosomes
XX-female, XY-male
sex-linked
x-chromosome linked
hemizygous
Possessing only one copy of the X chromosome (males)
Y chromosome
Contains very little genetic information
Notable region: SRY (sex-determining region Y)-formation of male gonads
Absence of Y=female zygotes
Presence of Y=male zygotes
SRY
Sex-determining region Y
Notable region on Y chromosome
Codes for a transcription factor that initiates testis differentiation and, thus, formation of male gonads
testes
Males: what primitive gonads develop into
Two functional components: seminiferous tubules and interstitial cells
seminiferous tubules
In testes
Sperm are produced here
Highly coiled
Nourished by Sertoli cells
Sertoli cells
Nourish sperm in testes
Specifically, in seminiferous tubules, where they (sperm) are produced
cells of Leydig
In testes
Secrete testosterone and other male sex hormones (androgens)
androgens
male sex hormones (other)
scrotum
External pouch that contains the testes
Maintains temp 2-4 degrees C below body temp
Layer of muscle around vas deferens that can raise and lower the testis to maintain proper temp for sperm development
epididymis
Sperm gaim motility and stored until ejaculation
ejaculation
Sperm travel from epididymis (where they were stored) to vas deferens–>ejaculatory duct–>urethra–>penis
semen
combination of sperm and seminal fluid
spermatogenesis
Formation of haploid sperm through meiosis
Occurs in the seminiferous tubules
spermatogonia–>primary spermatocytes–>secondary spermatocytes–>spermatids–>spermatozoa
Results in four functional sperm for each spermatogonium
spermatogonia
Diploid stem cells in males
Replicate genetic material during S stage, then become diploid primary spermatocytes
Four functional sperm for each spermatogonium after spermatogenesis
primary spermatocytes
Diploid
What spermatogonia develop into after S stage (replication)
Develop into haploid secondary spermatocytes after first meiotic division
secondary spermatocytes
Haploid
What primary spermatocytes develop into after first meiotic division
Develop into spermatids after meiosis II
spermatids
Haploid
What secondary spermatocytes develop into after meiosis II
Develop into spermatozoa after maturation
spermatozoa
Mature spermatids
sperm head
Contains the genetic material
Covered by acrosome (cap)
sperm midpiece
FIlled with mitochondria, which generates energy to be used as the sperm swims through the female reproductive tract
Generates ATP from fructose
acrosome
Covers sperm head
Derived from Golgi apparatus and needed to penetrate the ovum
sperm
Head (genetic material) + midpiece (energy via ATP from fructose) + tail (motility)
ovaries
Female gonads
Produce estrogen and progesterone
primary oocyte
Arrested in prophase I
Once a woman reaches menarche, each primary oocyte per month will complete meiosis I, producing a secondary oocyte and a polar body
Characterized by unequal cytokinesis, which doles out almost all cytoplasm to secondary oocyte and none to polar body
secondary oocyte
Arrested in metaphase II and does not complete meiosis II unless fertilization occurs
zygote
Haploid pronuclei of sperm + ovum=diploid cell
gonadotropin-releasing hormone (GnRH)
Release is restricted by hypothalamus prior to puberty
Restriction lifted after puberty
GnRH triggers anterior pituitary to synthesize and release
oogenesis
No unending supply of stem cells like in males
By birth, all of the oocytes have already undergone DNA replication and are already considered primary oocytes
testosterone
Produced by testes
Increases dramatically during puberty
FSH (follicle stimulating hormone)
Produced and released by anterior pituitary
Stimulates Sertoli cells and triggers sperm maturation
Causes the secretion of estrogen from ovaries
anterior pituitary
Synthesizes and releases FSH and LH in response to GnRH production by hypothalamus
LH (luteinizing hormone)
Produced and released by anterior pituitary
Causes interstitial cells to produce testosterone
Causes secretion of progesterone by corpus luteum (remnant follicle that remains after ovulation)
estrogen
Secreted from ovaries in response to FSH
Involved in initial thickening of endometrium (lining of uterus) in preparation of implantation of zygote
progesterone
Secreted by corpus luteum in response to LH
Involved in development and maintenance of endometrium
After first trimester of pregnancy, progesterone is supplied by placenta and corpus luteum atrophies
follicular phase
Begins with menstrual flow (beginning of uterine lining shedding)
GnRH from hypothalamus increases in response to decreased concentrations of estrogen and progesterone,
FSH and LH increase, which develop ovarian follicles
Follicles produce estrogen
GnRH, LH, FSH level off b/c of estrogen negative feedback
Estrogens starts to regrow endometrial lining
ovulation
Late in follicular phase, estrogen levels reach a level so high it paradoxically causes a spike in GnRH, LH, and FSH
LH spike causes release of ovum from ovary
luteal phase
LH causes ruptured follicle to form corpus luteum
Corpus luteum releases progesterone
Progesterone levels rise and maintain uterine lining
Estrogen levels remain high
hCG
Analog of LH
Secreted when zygote implants in uterine lining
Critical during first semester because progesterone and estrogen keep lining in place
High levels of progesterone and estrogen form a block on GnRH
