Lecture 4b BIO 120 Flashcards
what is meiosis
Halves the number of chromosomes
i.e. diploid-haploid
BIVALENT?
one pair of chromosomes(homologous chromosomes) in a tetrad.
Tetrad?
association of a pair of homologous chromosomes(4 sister chromatids)held together physically by at least one dan crossover.
crossing over?
GENETIC RECOMBINATION-meiosis-novel forms.
chiasmata
X shaped structure formed due to point of contact b/w paired chromatids during prophase I
where does exchange of genetic material occurs b/w strands of chromatids during prophase I?
chiasmata
what is known as the mixing of genetic material from diff strands of DNA?
Recombination
synapsis
pairing of homologous chromosomes
why does the chromosomes remain bound during synapsis?
due to exchange of genetic info
what aids in forming the connection during synapses and what is it structure?
SYNAPTONEMAL COMPLEX(protein and RNA structure)
what are the two sets of cell division in meiosis?
MEIOSIS I AND MEIOSIS II
How many chromosomes are present in daughter cells during meiosis as the parent cell
half
what happens in the first cell division (MEIOSIS I)
Homologous chromosome separate and it results in 2 haploid daughter cells with replicated chromosomes.
what happens in second cell division(meiosis II)
1.Separated replicated chromosomes(sister chromatids) into single chromosomes.
2.cell are already HAPLOID.
what happens in interphase of meiosis I?
Chromosomes are replicated to form sister chromatids.
what happens to the centrosome in interphase for meiosis I?
replicates, forming 2 centrosomes
What are the 4 phases of MEIOSIS I?
PROPHASE I
METAPHASE I
ANAPHASE I
TELOPHASEI
which stage of meiosis I occupies 90% of the meiosis?
PROPHASE I
what happens in PROPHASE I
Chromosome condenses, synapsis ,crossing over, tetrad formation
how Many chiasmata does each tetrad has?
one or more
what happens in METAPHASE I?
tetrads lined up along the mid-region (metaphase plate)
In what phase of meiosis I does homologous chromosome separate?
Anaphase I
What happens in ANAPHASE I of meiosis I?
homologous chromosome separate, move to the opposite poles with the help of spindle apparatus
what happens at beginning of telophase 1?
each half of cell-haploid set of chromosomes, each chromosome still has 2 sister chromaticds
how does cytokinesis occurs in meiosis I?
simultaneously of telophase 1: forming 2 haploid daughter cells
formation of what takes place in animal and plant cells during cytokinesis?
animal cells-cleavage furrow formation
plant cells-cell plate formation
no __________ occurs b/w end of meiosis i and beginning of meiosis ii because the chromosomes are already ______?
chromosome replication, replicated
PLOIDY?
Number of set of chromosomes
Haploid=n
diploid=2n=homozygous chromosomes
haploid number of chromosomes in the human body?
gametes
when is a replicated chromosome formed?
when.a single chromosome undergoes DNA synthesis
What is a genotype?
genetic makeup of an individual cell or organism
is DNA duplicated during meiosis I?
no, interphase
where does meiosis occurs in animals or humans?
production of gametes
ovary or testes
What happens in prometaphase II?
Nuclear envelope starts disntegrating,spindle microtubules attach to the centromere
what processes take place in TELOPHASE I?
replicated chromosomes arrive at pole and begin to uncoil,nuclear envelope reappears, spindle apparatus disappears, cytokinesis begins.
Does DNA replication occurs in MEIOSIS II?
no
is their s phase between meiosis I AND II
NO
What is interkinesis
interphase like stage that occurs between meiosis I and II unlike interphase it has no DNA replication and is for a very short period of time.
are the sister chromatid in metaphase II genetically identical or variable?why or why not?
genetically variable because of crossing over in MEIOSIS I
What is the end result of meiosis II?
4 daughter cells, each with a haploid set of unreplicated chromosomes
what are the 3 events unique in meiosis than mitosis?
1.synapsis and crossing over in prophase I-physically connect and exchange genetic info
2.at the metaphase plate their are homologous chromosomes(tetrads) instead of individual replicated chromosomes(sister chromatids)
3.at anaphase I, homologous chromosomes instead of sister chromatids that are separated and carried out to diff poles.
what is meiosis II similar with?
Mitosis
