Meiosis Flashcards
Meiosis creates ______ _______ cells from one diploid cell
4 haploid
Where does meiosis occur?
germ line cells
Where are germ line cells found?
gonads (testes and ovaries)
At the end of meiosis what is produced?
gametes (sperm and ova) called gametogensis
how many sets of chromosomes do gametes have
one (haploid)
during fertilization the nuclei of egg and sperm cell fuse and produce what?
a zygote
What does asexual reproduction generate
genetically identical offspring
meiosis and fertillization mix genetic information into…
new combinations
sexual reproduction generates variability that is the basis of most inherited differences among individual sexually repoducing organisms (T/F)
true
how many parts is meiosis
two parts; meiosis I and meiosis II
DNa replicates and chromosome proteins are duplicated in the _______ ______ (meiosis)
premeiotic interphase
During Meiosis I homologous chromosomes and non sister chromatids undergo…
crossing-over
After meiosis I each diploid has…
the diploid number of chromosomes-each chromosome has 2 sister chromatids
In meiosis II, sister chromatids… (anaphase)
seperate
what happens in synapsis
sister chromatids connect together in synaptonemal complex
what is homologous recombination
genetic exchange (crossing over) occurs between homologous cchromosomes
what is reduction division
meiosis involves two successive divisions, with no replication of genetic material between them
meiosis II do does not have an ____ phase before it
S phase
when does recombination (crossing over) occur?
prophase I of Meiosis I
What does recombination do?
generates diversity
what are alleles?
versions of each gene present in the members of a homologous pair
are alleles the same or different?
they can be either
for a gene that encodes proteins, what do alleles do
they can encode different versions of the protein, or no protein at all
chiasmata is the…
point of contact in crossing over
recombination results in identical sister chromatids (T/F)
false
the first meiotic division is termed the…
“reduction division”
second meiotic division does not further reduce the number of chromosomes (T/F)
true
what happens in prophase I of meiosis I
replicated chromosomes (sister chromatids) fold and condense in the nucleus
two chromosomes of each homologous pair undergo synapsis (from tetrads)
chromatids of homologous chromosomes cross over and form chiasmata
what happens in prometaphase I
the nuclear envelope breaks down, spindel enters and chromosomes attach to kinetochor microtubulues
what is different between prometaphase of mitosis and prometaphase I of meiosis
sister chromatids remain together in prometaphase I
where do spindle microtubules attach to kinetochore proteins
on the outside of each centromere
what happens in metaphase I
terminal chiasmata hold homologous pairs together and line up on metaphase plate
orientation of homologues is random (T/F)
true
what is the formula for independent assortment
2^n (n is chromosome pairs)
what are the major sources of genetic variability
crossing over
independent assortment
sets of male and female gametes that unite in fertilization
what happens in anaphase I
spindle fibers shorten and pull centromeres to poles, seperation of homologous chromosomes
random orientation results in independent assortment
what happens in telophase I
chromosomes are segregated into 2 clusters, one at each pole
nuclear membrane reforms
what follows meiosis I
G1, G2, meiosis II (no s phase)
what happens in prophase II
chromosomes condense and spindle forms, nuc envelope starts to breakdown
what happens in prometaphase II
nuclear envelope completely breaks down
spindle microtubulues attach to the two kinetochores of each chromosome
what happens in metaphase II
spindle microtubules align chromosomes on the metaphase plate
what happens in anaphase II
spindles seperate the two chromatid and pull them towards opposite spindle poles
what happens in telophase II
chromatids decondence to extend interphase state
spindles disassemble and nuc envelopes form around chromatin
what happens in nondisjunction
the spindle fails to seperate the homologous chromosomes or sister chromatids
zygotes that receive extra copy of chromosome in nondisjuction have…
3 chromosomes instead of 2
what chromosome is affected in down syndrome
chromosome 21-trisomy 21
what are sex chromosomes
pairs of chromosomes that are different in male and female individuals of the same species
i.e. XX vs XY
in females the two X chromosomes are fully or partly homolgous
fully
in males the X and Y chromosomes are fully or partly homolgous
partly
can crossing over occur more than once in the same chromosome pair
yes
in animals which phase dominates the life cycle? which phase is reduced?
diploid phase, haploid phase is reduced
in animals meiosis is followed directly by what
gamete formation/fertilization
plants can have either diploid of haploid dominate the life cycle (T/F)
true
in some fungi and algae the diploid phase is limited to what single cell?
the zygote produced by fetrtilization
