Ch. 2 - Basic Processes Flashcards
--> Mitosis / Meiosis --> Spermatogenesis / Oogenesis --> Generation of Gametes
What are homologous chromosomes?
- -> are similar, but not identical
- -> carry genes for same inherited characteristic
- -> may carry different version of same gene
- -> one is inherited from mother, other fromf ather
During G1, each chromosome of a homologous pair contains how many chromatin?
1
What are sex chromosomes?
sex determining chromosomes = not homologous, but behave as homologs during meiosis b/c pseudoautosomal region contain homologous sequences that are able to pair and recombine during meiosis.
What are centromeres and where are they located?
constricted regions on chromosomes
What is mitosis?
–> it partitions chromosomes into dividing cells.
–> produces daughter cells with a full diploid complement of chromosomes
What is karyokinesis?
genetic material partitioned to daughter cells during nuclear division
what is cytokinesis?
cytoplasmic division follows
What is the cell cycle composed of?
interphase and mitosis.
What does interphase include?
- -> S phase: DNA is synthesized
- -> two gap phases (G1 and G2)
What happens in G0 stage?
a stage in G1 phase where cells become nondividing, but maintain a metabolically active state
–> some cell types are permanently in G0 while others can re-enter the cell cycle under certain circumstances
What happens in metaphase?
- -> kinetochore: proteins associated with centromere
- -> spindle fibers: bind to kinetochore and facilitate chromatid migration to opposite poles
- -> cohesin: nprotein complex that holds sister chromatids together
- -> separase: enzyme that degrades cohesin
- -> shugoshin: protein that protects cohesin from being degraded by separase
What happens in anaphase?
Shugoshin is degraded, therefore separase is able to degrade cohesion at the centromeres.
Disjunction: sister chromatids separate and migrate to opposite poles
Separated sister chromatids are called ‘daughter chromosomes’
What are the cell cycle checkpoints?
G1/S checkpoint
- -> monitors size cell has achived
- -> evaluates condition of DNA
G2/M checkpoint
- -> monitors if DNA replication is incomplete
- -> monitors damaged DNA
M checkpoint
–> monitors successful formation of spindle fiber system and attachment to kinetochores
What is meiosis?
- -> reduces amount of genetic material by half
- -> produces haploid gametes or spores, each containing one chromatid of a homologous pair of chromosomes
What are meiosis I and meiosis II?
meiosis I: reductional division
meiosis II: equational division
DNA synthesis occurs during interphase before the beginning of meiosis I and does NOT occur again before meiosis II
Meiotic prophase I: Leptonema
chromosomes appear as long, single threads, unassociated with each other
Meiotic prophase I: Zygonema
formation of synaptonemal complex: synapsis
each pair of homologous chromosomes is known as bivalent
Meiotic prophase I: Pachynema
each bivalent becomes shorter, thicker, and two sister chromatids split and become visible: 4 membered structure (2 homologs each containing two sister chromatids is called a ‘tetrad’)
Meiotic prophase I: ‘crossing over’
excahnge of genetic material b/w nonsister chromatids
Meiotic prophase I: Diplonema
within tetrads, sister chromatids separate ‘Chiasma’: Where chromatids remain intertwined
Meiotic prophase I: Diakinesis
- -> nucleus and nuclear envelope break down
- -> centromeres attach to spindle fibers (both sister chromatids of a homologous pair pointing to same pole; two homologs pointing to opposite poles)
What happens during metaphase I?
tetrads align in random orientation at the metaphase plate
What happens during anaphase I?
homologous chromosomes separate and move toward the poles (dysjunction).
the sister chromatids remain attached at centromeres (cohesion protected by shugoshin) and are called dyads.
What happens in telophase I?
each pole now has a haploid set of chromosomes (each containing 2 sister chromatids)
How many haploid daughter cells does cytokinesis yield?
it yields two haploid daughter cells.
nuclear envelope may form around chromosomes in some species
What happens in second meiotic division?
dyads align at metaphase plate.
shugoshin is degrade and this allows sister chromatids to separate towards opposite poles (anaphase II).
following telophase II and cytokinesis, each haploid daughter cell from meiosis II has one member (a monad) from each pair of homologous chromosomes.
When does replication occur?
prior to mitosis and meiosis.
Different eukaryotic organisms have different life cycles that involve ____ phases.
alternation of haploid and diploid phases.
Why in a diploid species you cannot directly see the results of meiosis?
And what is one usful method to use in order to see the prodcuts for meiosis?
because the gametes do not have a phenotype.
therefore, in order to look at the products of meiosis you need to cross an organism with another organism.
–> ex: you may carry out a self cross, a testcross, or a backcross
however, fungi spend most of their life cycles as haploid organisms and if the spore has a detectable phenotype then you can deduce its genotype and therefore see the product of meiosis directly. This is known as ‘Tetrad Analysis’
What is tetrad analysis? Give an example.
it’s when you are deducing the genotype of an organism to see the product of meiosis directly when the spore has a detectable phenotype.
Ex1: Saccharomyces cerevisiae
Ex2: Neurospora crassa / Sordaria fimocola
***these organisms produce asci containing ‘ordered’ tetrads
