Reproduction Flashcards
diploid
2n
contain two copies of each chromosome
i.e. autosomal cells
haploid
n
contain only one copy of each chromosome
i.e. germ cells
cell cycle
specific series of phases during which a cell grows, synthesizes DNA, and divides
derangements can lead to unchecked cell division and may be responsible for the formation of cancer
four stages: G1, S, G2, M
interphase
G1, S, G2 collectively
longest part of the cell cycle
chromatin
G0 stage
cell is simply living and serving its function, without any preparation for division
chromatin
less condensed form of chromosomes
allows for DNA to be available to RNA polymerase so genes can be transcribed
G1 stage
cells create organelles for energy and protein production (mitochondria, ribosomes, and ER), while also increasing size
restriction point
governs passage into S (synthesis) stage
criteria (i.e. containing the proper complement of DNA) must be met
S stage
cell replicates its genetic material so that each daughter cell will have identical copies
after replication, each chromosome consists of two identical chromatids bound together at specialized region known as centromere
G2 stage
cell phases through another quality checkpoint
DNA already duplicated
cell checks to ensure that there are enough organelles and cytoplasm to divide between two daughter cells
makes sure DNA replication proceeded correctly to avoid passing on error to daughter cells that may further replicate error to progeny
M stage
consists of mitosis itself along with cytokinesis
divided into four phases: prophase, metaphase, anaphase, telophase
p53
main protein in control of checking at restriction point (between G1/S) as well as at G2/M checkpoint to ensure that there is no damage to the DNA and that the cell has achieved adequate size and organelles have been properly replicated to support two daughter cells
cyclin-dependent kinases (CDK)
responsible for the cell cycle
require presence of right cyclins
conc’s of various cyclins increase/decrease during specific stages
cyclins bind to these creating an activated complex, which can then phosphorylate transcription factors
transcription factors
promote transcription of genes required for the next stage of the cell cycle
cancer
results when cell cycle control becomes deranged and damaged cells are allowed to undergo mitosis
one of the most common mutations found is of gene that produces p53 (TP53)
- cell cycle is not stopped to repair damaged DNA which allows for mutations to accumulate
tumors
created when cancer cells undergo rapid cell division
metastasis
if cancer cell begins to produce the right factors, the damaged cells are then able to reach other tissues
distant spread of cancerous cells through the bloodstream or lymphatic systems
mitosis
process by which two identical daughter cells are created from a single cell
four phases: prophase, metaphase, anaphase, telophase
occurs in somatic cells–cells not involved in sexual reproduction
finite number of divisions before programmed death: 20-50 for human somatic cells
prophase
first phase in mitosis
condensation of the chromatin into chromosomes
centriole pairs separate and move toward opposite poles of the cell
centrioles form spindle fibers made of microtubules, which radiate outward
nuclear membrane dissolves, allowing spindle fibers to contact the chromosomes
nucleoli become less distinct, may disappear completely
kinetochores appear at the centromere
centriole pairs
cylindrical organelles located outside the nucleus in centrosome region
responsible for the correct division of DNA
asters
formed from microtubules
anchor the centrioles to the cell membrane
kinetochores
protein structures located on the centromeres that serve as attachment points for specific fibers of the spindle apparatus
metaphase
centriole pairs are now at opposite ends of the cell
kinetochore fibers interact with the fibers of the spindle apparatus to align chromosomes at the metaphase plate
metaphase plate
equatorial plate
equidistant between the two poles of the cell
anaphase
centromeres split so that each chromatid has its own distinct centromere, allowing sister chromatids to separate
pulled toward the opposite poles of the cell by the shortening of the kinetochore fibers
telophase
reverse of prophase
spindle apparatus disappears
nuclear membrane reforms around each set of chromosomes and nucleoli reappear
chromosomes uncoil, resuming interphase form
each of two new nuclei has received a complete copy of the genome identical to the original genome and to each other
cytokinesis
cytokinesis
separation of the cytoplasm and organelles so that each daughter cell has sufficient supplies to survive on its own
gametocytes
germ cells in which meiosis occurs
results in up to four nonidentical sex cells
gametes
nonidentical sex cells
meiosis
occurs in germ cells to create four nonidentical sex cells (games
consists of one round of replication followed by two rounds of division
meiosis I
results in homologous chromosomes being separated, generating haploid daughter cells
reductional division
meiosis II
similar to mitosis
results in separation of sister chromatids
equational division
homologous pairs
considered separate chromosomes
human genome consists of 23
each contains one chromosome inherited from each parent
prophase I
meiosis I
chromatin condenses into chromosomes, spindle apparatus forms, nucleoli and nuclear membrane disappear
homologous chromosomes come together and intertwine in synapsis
crossing over occurs
tetrad
each chromosome consists of two sister chromatids, so each synaptic pair contains four chromatids
chiasma (pl. chiasmata)
point of synapsis
crossing over
chromatids of homologous chromosomes may break at point of synapsis and exchange equivalent pieces of DNA
occurs between homologous chromosomes and not between sister chromatids of the same chromosomes
genetic recombination, can unlink linked genes, thereby increasing the variety of genetic combinations that can be produced via gametogenesis
each daughter cell will have a unique pool of alleles from a random mixture of maternal and paternal origin
Mendel’s second law (of independent assortment)
inheritance of one allele has no effect on the likelihood of inheriting certain alleles for other genes
metaphase I
meiosis I homologous pairs (tetrads) align at the metaphase plate and each pair attaches to a separate spindle fiber by its kinetochore (only ONE spindle fiber per pair of sister chromatids)
anaphase I
meiosis I
homologous pairs separate and are pulled to opposite poles of the cell
disjunction
accounts of Mendel’s first law (of segregation)
each chromosome of paternal origin separates from its homologue of maternal origin and either chromosome can end up in either daughter
segregation
separating of the two homologous chromosomes
distribution to the two intermediate daughter cells is random with respect to parental origin
telophase I
meiosis I
nuclear membrane forms around each new nucleus
each chromosome still consists of two sister chromatids joined at the centromere
cells are now haploid; once homologous chromosomes separate, only n chromosomes are found in each daughter cell (23 in humans)
cell divides into two daughter cells by cytokinesis
interkinesis
between cell divisions, there may be a short rest period during which the chromosomes partially uncoil
meiosis II
very similar to mitosis in that sister chromatids, rather than homologues, are separated from each other
by completion, up to four haploid daughter cells produced per gametocyte (oogenesis an exception)
prophase II
meiosis II
nuclear envelope dissolves, nucleoli disappear, centrioles migrate to opposite poles, spindle apparatus begins to form
metaphase II
meiosis II
chromosomes line up on metaphase plate
anaphase II
meiosis II
centromeres divide, separating chromosomes into sister chromatids
pulled to opposite poles by spindle fibers