meiosis Flashcards
what happens in Interphase I? (2)
DNA is in loose form chromatin
All organelles and DNA get copied
Prophase I (2)
Chromatin condenses
homologues come together (synapsis) in pairs called tetrads
chiasmata
metaphase I
homologues line up at metaphase plate with the help of kinetochore microtubules
anaphase i
homologous pairs get separated and pulled to opposite poles
telophase I (4)
nuclear envelope reforms
spindle apparatus breaks up
nucleolus reappears
DNA loosens into chromatin
cytokinesis I
cytoplasm splits resulting in two different daughter cells, each contain one of the homologues
prophase II (3)
nuclear envelope breaks up
spindle apparatus forms and attached to sister chromatids
nucleolus disappears
metaphase II
sister chromatids line up at metaphase plate
anaphase II
sister chromatids separate at the centromere and move toward opposite poles
telophase II (4)
nuclear envelope reforms
spindle apparatus breaks up
nucleolus reappears
DNA loosens into chromatin
cytokinesis II
cytoplasm splits resulting in 4 different haploid daughter cells
what is the units of inheritance onto offspring called?
genes
where are genes located?
chromosomes
what are genes made up of?
DNA
what class of biomolecules does DNA belong to?
nucleic acids/ polynucleotide
monomers of nucleic acids
nucleotides
3 parts of nucleotides of DNA
Nitrogenous base, pentose sugar, phosphate group
what does the N-base connect directly to?
phosphate group
2 types of nucleic acids
DNA and Rna
what do DNA and RNA enable organisms to do?
reproduce their components from one generation to the next
two families in n-bases
purine and pyrimidines
which n base family is bigger?
purines w/ 6 membered ring fused to 5 membered ring compared to 6 membered rings of pyrimidines
types of purines
adenine and guanine
members of pyrimidine family
DNA - cytosine, thymine
RNA - cytosine, uracil
what does adenine bond to?
thymine with 2 bonds between them
what does cytosine bond to?
guanine with 3 bonds between them
pentose sugar in DNA
deoxyribose
pentose sugar in RNA
ribose
difference between pentose sugar in DNA and RNA
deoxyribose lacks an oxygen atom on number 2 carbon
transmission of traits from one generation to the next
heredity
variation
changes from offspring to siblings
genetics
study of heredity and variation
number of chromosomes in human body cells
46 chromosomes in somatic cells
number of chromosomes in reproductive cells
23 chromosomes in gametes
how many genes on 46 chromosomes total?
20-25,000 genes
what does each chromosome consist of?
single long DNA molecule - has 100-1,000 of genes on it
what is the gene’s locus
specific location on the chromosome
plural of locus
loci
what does our genes program?
the specific traits that emerge as we develop from fertilized eggs to adults
what information do genes contain?
info of all the traits of the body
why does the DNA rely on the mRNA?
it’s too big to exit the nucleus, so it relies on the mRNA to transcribe/ carry out DNA’s message out of the nucleus
what does the mRNA do after exiting the nucleus?
arrives at a ribosome where the message gets translated into the making of a polypeptide
asexual reproduction occurs more often with?
unicellular organisms
how do some multicellular organisms asexually reproduce (along with unicellular)?
budding
how are buds derived?
by mitosis - not meiosis, therefore the offspring are identical to the parent assuming no mutation
what does asexual reproduction bring about?
clones of genetically identical individuals
how does sexual reproduction relate to variation/diversity?
results in greater genetic variation because unique combinations of genes come from both parents
what is sexual reproduction the result of?
gametes coming together that were formed during meiosis
what does the life cycle of an organism follow?
the reproductive stages of an organism from generation to generation
how do chromosomes differ? (3)
by their lengths, location of their centromeres, and by their distinctive banding patterns when stained
although humans have 46 chromosomes, how many pairs do we have?
23 pairs - 2 each kind. one from maternal and one from paternal
what is it called when chromosomes are arranged in pairs starting with the longest?
karyotype
what are chromosomes that carry the same traits called? (4)
homologues
homologous pairs
homologous chromosomes
tetrads
different stages of “chromosomes”
chromosome -> 2 sister chromatids -> tetrads
what type of genes do homologous pairs carry?
same genes at the same loci
how do traits show up in chromosomes?
different version called alleles
what is the exception to alleles?
X and Y chromosomes (sex chromosomes)
female homologous chromosomes
XX
male homologous chromosomes
XY
why do we have homologous pairs of chromosomes?
we inherit 1 chromosome from each parent, so altogether we inherit 23 chromosomes from mom and 23 from dad
what do each egg/sperm cell contain?
22 autosomes and either an X or a Y for a total sum of 23 chromosomes
what type of cells are gametes?
haploid (1n)
what happens in fertilization?
2 haploids come together to form a zygote that is diploid (2n)
what happens once the zygote forms?
mitosis/cleavage occurs to allow the offspring to grow and develop
what are the only cells in the body not made by mitosis?
gametes that are made in the gonads by meiosis
2 types of meiosis
spermatogenesis
oogenesis
are all life on earth separated into 1n and 2n?
no, fungi and some algae are different, their multicellular body cells and agmates are already in 1n state, so via mitosis they are ready to fertilize/form a zygote - the 2n state temporarily
what do fungi need to do since their body cells exist normally as multicellular haploids?
halve their chromosome number and this is accomplished by meiosis
animal multicellualr form
2n
animal gamete form
1n
fungi multicellular form
1n
fungi gamete form
1n
if you want to take a 2n down to 1n, what is this process called?
meiosis
what is cloning/making more of whatever the cell type happens to be?
mitosis
examples of mitosis in haploid and dipold cells
haploid cells copy themselves, divide, or make more haploids
diploid cells copy themselves, divide, and make more diploids
what does meiosis consist of?
meiosis I and meiosis II
2 cell divisions resulting in 4 daughter cells
where in the cell cycle have chromsomes replicated?
s phase of interphase
what are the different terms to call these x shaped structures?
sister chromatids, duplicated/replicated chromosomes
with meiosis, a replicated chromosomes stays nearby its matching replicated chromosomes in what stages?
prophase i, metaphase ii
what do you call 2 replicated chromosomes next to each other?
tetrads, homologues, homologous pairs/chromosomes
what do you call the process of the 2 X’s coming together?
synapsis
since there are four chromatids, what is this called?
tetrads
when in meiosis does the exchange of genetic material called crossing over occur resulting in chiasma?
prophase i
what is the whole point of meiosis i?
separate homologous pairs
what is the whole point of meiosis ii?
separate sister chromatids
is meiosis i or meiosis ii more like mitosis?
meiosis ii, both separate sister chromatids
DNA replication occurs in what part of the cell cycle and how many times in mitosis?
S phase of interphase - once
DNA replication occurs in what part of the cell cycle and how many times in meiosis?
S phase of interphase - once
number of cell divisions in mitosis?
1
number of cell divisions in meiosis?
2
does synapsis occur and if so when in mitosis?
no
does synapsis occur and if so when in meiosis?
yes - prophase I
what is number of daughter cells and are they different or identical in mitosis?
2 - identical
what is number of daughter cells and are they different or identical in meiosis?
4 - different
role of mitosis
growth and tissue repair
role of meiosis
make gametes
why are offspring of sexually reproducing organisms not genetically the same? (3)
Independent Assortment
Crossing Over
Random Fertilization
what is Independent Assortment?
Law of Assortment - when homologues line up at the equator of the cell in metaphase I, it is random (“independent”) event for each homologous pair
what is the number of possible combinations due to the Law of Assortment?
2^n, where n is the haploid number
how many possible different gametes are there in humans?
2^23 ~ 8 million
what is crossing over?
occurs during prophase i of meiosis when homologues come together in a process called synapses to form pairs called tetrads. then nonsister chromatids trade places - resulting regions are called chiasmata
on average, how many crossing over events are there?
2-3 per homologous pair
what is random fertilization?
there would be 64 trillion possible combinations of chromosomes solely looking at the 8 million possible different ovules and 8 million possible different sperms not counting crossing over
what process creates the greatest number of new genetic combinations?
mutations
