Lecture 2/19 Flashcards
what is oogonia?
diploid germ cells in ovaries of female embryos
do oogonia divide by mitosis or meiosis?
mitosis, to make 7 million oocytes during fetal development
what happens to oogonia in an embryo that don’t die by birth?
they enter and arrest in meiosis i to become primary oocytes and the chromosomes decondense
what happens to oocytes starting at puberty?
once a month, hormonal stimulation causes one oocyte to recondense its chromosomes and complete meiosis i and starts meiosis ii
is the DNA content the same between daughter cells after meiosis i for an oocyte?
yes, but one cell gets all cytoplasmic content (secondary oocyte) and the other is mainly nuclear (first polar body)
does a secondary oocyte finish meiosis ii if it’s fertilized?
yes, and produces a mature ovum and a second polar body
does a secondary oocyte finish meiosis ii if it’s not fertilized?
no, it arrests in metaphase of meiosis ii
can mistakes occur from meiotic arrest at prophase i?
yes, there may be chromosome separation errors like trisomies
does the oocyte develop in isolation?
no, it is within the primary follicle/follicular cells
what happens to the corpus luteum if no fertilization occurs?
it degenerates
what happens to the first polar body during/after meiosis i?
it dies
what happens to the second polar body during/after meiosis ii?
it dies
in what circumstance does a germ cell in women finish meiosis ii? when does it not finish?
it finishes if the egg is fertilized, if unfertilized it is released as is
what are the cells called on day 1 after meiosis ii is finished in a fertilized egg?
there are 2 blastomeres
what are the cells called on day 2 after meiosis ii is finished in a fertilized egg?
there are 4 cell blastomeres
what are the cells called on day 3 after meiosis ii is finished in a fertilized egg?
there are 8 cell blastomeres
what are the cells called on day 5 after meiosis ii is finished?
inner cell mass (becomes embryo) and approx 16-32 cells in the blastocyst
what does the inner cell mass of the blastocyst become?
embryo
what do the cells around the inner cell mass of the blastocyst become?
placenta and extraembryonic matter
what are spermatogonia and where are they found?
diploid germ cells found only in the testis
what happens to spermatogonia after puberty? what do they become?
meiosis begins and they become primary spermatocytes
is division symmetrical for spermatocytes?
yes
what is the product of meiosis i for spermatocytes?
two secondary spermatocytes
what is the product of meiosis ii for secondary spermatocytes?
2 spermatids
are all sperm Y?
no, an equal number of X and Y sperm are produced
how long does spermatogenesis cycle take?
48-60 days
for each spermatocyte, what is the product of a full cycle of symmetrical meiosis?
4 haploid sperm
does mitosis stop in men when meiosis begins?
no, they both continue to occur throughout adult life
when are mistakes in DNA replication fixed in gametogenesis?
proofreading, and the cell cycle is stopped until the correction is made
what happens to a cell whose mistake in DNA replication isn’t corrected?
it is slated for cell death
what happens to a cell with a mistake from DNA replication if it’s not corrected and doesn’t die?
mutation in sperm or egg (every cell in the fertilized egg will have the mutation)
what happens if there’s a mistake in mitosis?
mitotic arrest until the mistake is corrected
what happens to a mistake that isn’t corrected in mitosis?
aneuploidy (wrong number of chromosomes) though this isn’t often seen in the germline
what happens if there is a mistake in meiosis (i or ii)?
cell divisions are arrested until corrected
what happens if there is a mistake in meiosis (i or ii) that doesn’t get corrected?
incorrect ploidy, uncorrected translocations, etc.
what is -somy?
ONE chromosome (ie. trisomy 21 means there are 3 copies of chromosome 21 and all other chromosomes are normal)
is monosomy viable?
only for chromosome X (Turner’s syndrome)
which germline are more de novo mutations found in with age and why?
male (XY) bc DNA repair mechanisms get turned off at some point in sperm
are trisomies usually viable?
no, they usually die after birth if they are born alive (except for things like trisomy 21)
do you lose genetic information in the error of reciprocal translocations?
no
do you lose genetic information in the mistake of non-reciprocal translocation?
yes, an entire arm of one chromosome fuses to an arm of another chromosome (the remaining half-chromosome disappears)
what kind of chromosome tends toward nonreciprocal translocation?
the ones with short arms
what is a robertsonian translocation and does it result in genetic information getting lost?
an entire chromosome is translocated to another chromosome, no info is lost
what happens when translocated chromosomes undergo meiosis?
the homologous chromosomes can’t pair correctly in meiosis i
what is mosaicism?
some cells have the correct number of chromosomes, others may have an incorrect number due to mitotic mistakes
what is chimerism?
people who have cells that originated from different sources
what is micro-chimerism?
exchange of cells between birth mother and XY fetus or between fraternal twins when one twin dies
