Abbas Eleiwe EmbrylogyL1 Embryology focus on essential events to understand principles of embryogenesis that can be used to diagnose care amp prevent birth defects germ cells ID: 933405
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Slide1
Embryology
Prof. Dr.
Samia
Abbas
Eleiwe
Slide2Embrylogy-L1
Slide3Embryology focus on essential events to understand principles of embryogenesis that can be used to
diagnose, care, & prevent
birth defects
.
Slide4germ cells
occur at end of 3rd week of development in
wall of yolk sac
near attachment of future umbilical cord.
They
migrate by amoeboid movement toward developing gonads of embryo.
Slide5germ cells divide by
mitosis
d
uring journey.
In embryonic gonads, germ cells undergo meiosis
and
cytodiffernetiation for production of sperms or oocyte (gametogenesis).
Slide6Slide7Humans have
46 chromosomes
in their cells appearing as
23 homologous
pairs, each chromosome is made of fine filaments that are made of
DNA
chain covered by proteins (mainly histone).
Slide8DNA shows loci (
genes):
hereditary units controlling development. human cells contain about 100,000 genes.
Somatic cells have
22 pairs
of autosomal chromosome and
a pair of sex chromosome (XX or XY).
Slide9Mitosis:
1.
prophase
; diploid number of 46 chromosome replicating their
DNA
contents (from
N to 2N)
beginning of chromosome to be
coiled,
condensed and contract.
Slide102.
Prometaphase
:
each chromosome seen as
two
parallel chromatids connected by a centromere Each chromatid contains
DNA amount (N),
nuclear membrane
is degenerating
Slide11Slide123.
Metaphase
:
doubled structured chromosomes are in
equator
( chromosome seen by light microscope).4.
Anaphase
: centromeres separate
→ separation
of chromatids that
migrate
toward poles.
Slide135.
Telophase
:
chromosome
uncoiled & diffused
inside reformed nuclear membrane, & cytoplasm divides. Daughter cells contain same
diploid 46 single structured chromosome number & N amount of DNA
(as mother cells)
.
Slide14Slide15Meiosis:
two steps
Meiosis I
:
where changes
similar to that of mitosis. But homologous chromosomes are paired in meiosis I
by
synapsis
forming 22 pairs of doubled structured chromosome (except the 2 sex chromosome).
Slide16At final phase of
meiosis I
each pair of chromosome will be separated into each of daughter cells.
each
daughter cell
contains
haploid 23 doubled structured chromosome number with N amount of DNA.
Slide17During
meiosis I
crossovers→
interchange of segments between chromatids of a pair of chromosome resulting in
genetic variability
& new chromosomes. point of interchange is united, an X-like structure is formed called chiasma formation. Then interchanged segments break and exchange.
Slide18Meiosis II:
result in two daughter cells each of them containing
haploid 23
single
structured chromosome number with
half amount 1/2 of DNA.
Slide19Slide20Cytodifferentiation
These
are cellular changes during gametogenesis: This comes after meiotic divisions.