meiosis Flashcards
who does meiosis
All Multicellular Eukaryotes: Animals, Plants, Fungi, some algae
Why is meiosis done
for sexual reproduction
why is sexual reproduction for meiosis important
because It allows genetic recombination
New combinations of genes may ..
a. better suit environments
b. allow offspring to survive radical environmental change
c. allow offspring to survive a disease outbreak
cells produced by meiosis are called
gametes
sex chromosomes
determine sex (in humans XX = female, Xy = male)
autosomes
any chromosome not used to determine sex of offspring
gametes
haploid cells made by meiosis
haploid cells
have one set of chromosomes
called 1n cells
mathematical representation
n=
number of different C types
diploid
cells have two of each kind of chromosome
2n
where does meiosis happen
only in gonads
gonads
reproductive organs ; testis and ovary
specialized cells in gonad do
meiosis
spermatocytes and oocytes
Spermatocytes and oocytes are constantly replaced by
specialized Spermatogonia cells & oogonia cells
Spermatogonia cells do Mitosis make
one primary spermatocyte and a cells that stays a spermatogonia
what does the primary spermatocyte do
does meiosis to make four spermatids
sperm diagram
acrosome- vesicle w/ penetratin enzymes
nucleus- 1n
midpiece- makes ATP and powers flagellum (filled w/mitochondria)
tail- flagellum
oogenesis
Oogonia do
Mitosis to make
1 primary Oocyte
primary oocyte does what
meiosis one to make one secondary oocyte and one polar body
Meiosis II ( after fertilization) makes
1 ovum &1 polar body
meiosis one main purpose
separate homologous pairs (cells become 1n with X shape C)
prophase one
Nuclear envelope breaks down, spindle forms, condense chromatids
synapsis, crossing over, chiasmata
metaphase one
chromosomes line up in pairs
anaphase one
Homologs move to
opposite poles
(cohesin along arms breaks down)
(cohesin at centromeres remains)
telophase one
Cytokinesis simultaneously X shaped C reach poles Many cells do not decondense C or reform nuclear E Spindle only partly broken down
homologous chromosomes
same C type
same length
code for same gene (but different versions)
what are the only pair of Homologues that do not look alike
X and Y sex chromosomes
synpasis
Homologous Chromosomes pair up
Line up gene to gene then physically connect along their arms
Proteins form a synaptonemal complex that bind them together
crossing over
Non-sister chromosomes trade corresponding segments of DNA
which genes cross over most
genes farthest from centromere
the gene’s locus (loci)
location of a gene on a chromosome
distance from centromere measured in
map units
chiasmata
X shaped region where crossing over has happened.
Synaptonemal complex has broken down but …
Cohesions still hold sister chromatids together
Meiosis in Fungi
Fungal bodies formed of hyphae
what is hyphae
filaments made of chains of 1n cells for fungal bodies
what forms the fungal body and what is it called
Hyphae interweave to form fungus body
The body mass is called a mycelium
if hypha + and - meet…
the two cells fuse cytoplasm and nuceli and then do meiosis to make 4 haploid nuclei, then do mitosis to form 8 nuceli
plasmogamy
fusing two cells cytoplasm
karyogamy
fusing nuclei of two cells (2n)
what happens to the 8 nuclei formed from the hypha meeting
Each nucleus grows a tough casing around it and becomes a
Spore
spores disperse on the wind and germinate to make new 1n hyphae
ascus
The ascospores that form from one cell stay together in a capsule called an ascus
crossing over pattern and non crossing over pattern
no crossing over is 4:4 any other patterns results from crossing over
genetic variation increased by
crossing over and independent assortment
what is independent assortment
Each pair of homologues lines up randomly and Independent of how other pairs line up
2^n
different gametes formed = 2^n
example Humans =
2^23 or 8,399,608
Where does the spindle and envelop reform and dependence chromatids?
Telophase 2
Meiosis one is for
Meiosis two is for
Meiosis one- separate homologous chromosomes 2n-1n end up haploid
Meiosis 2- separate sister chromatids
