Embryology
Embryology
Prof. Dr. Samia Abbas Eleiwe
Embrylogy-L1
•
Embryology focus on essential
events to understand principles
of embryogenesis that can be
used to
diagnose, care, &
prevent
birth defects
.
•
germ 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.
•
germ cells divide by
mitosis
d
uring journey.
•
In embryonic gonads, germ cells
undergo
meiosis
and
cytodiffernetiation
for production
of sperms or oocyte
(
gametogenesis).
•
Humans 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).
•
DNA 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).
M
i
t
o
s
i
s
:
•
1.
prophase
; diploid number of 46
chromosome replicating their
DNA
contents (from
N to 2N
)
beginning of chromosome to be
coiled,
condensed and contract.
•
2.
Prometaphase
:
each chromosome
seen as
two
parallel
chromatids
connected by a centromere
•
Each
chromatid
contains
DNA
amount (N),
nuclear membrane
is
degenerating
•
3.
Metaphase
:
doubled structured
chromosomes are in
equator
(
chromosome seen by
light
microscope)
.
•
4.
Anaphase
: centromeres
separate
→ separation
of chromatids
that
migrate
toward poles.
•
5.
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)
.
M
e
i
o
s
i
s
:
t
w
o
s
t
e
p
s
•
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).
•
At 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
.
•
During
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.
•
Meiosis II:
result in two
daughter cells each of them
containing
haploid 23
single
structured chromosome
number with
half amount 1/2
of DNA
.
•
Cytodifferentiation
•
These are cellular changes during
gametogenesis: This comes after meiotic
divisions.
Delve into the fascinating world of human embryology and genetic development with a focus on essential events like germ cell migration, mitosis, meiosis, and chromosomal structure. Understand the intricate processes that shape the formation of new life and learn how these principles play a crucial role in diagnosing, caring for, and preventing birth defects. Explore the journey of germ cells as they divide and differentiate, ultimately contributing to the production of sperm and oocytes. Discover the intricate relationship between DNA, genes, and chromosomes, unraveling the hereditary units that control development in human cells through mitosis and other key stages of cellular division.
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Presentation Transcript
Embryology Prof. Dr. Samia Abbas Eleiwe
Embryology focus on essential events to understand principles of embryogenesis that can be used to diagnose, care, & prevent birth defects.
germ 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.
germ cells divide by mitosis during journey. In embryonic gonads, germ cells undergo meiosis and cytodiffernetiation for production of sperms or oocyte (gametogenesis).
Humans 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).
DNA 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).
Mitosis: Mitosis: 1. prophase; diploid number of 46 chromosome replicating their DNA contents (from N to 2N) beginning of chromosome to be coiled, condensed and contract.
2. Prometaphase: each chromosome seen as two parallel chromatids connected by a centromere Each chromatid contains DNA amount (N), nuclear membrane is degenerating
3. Metaphase: doubled structured chromosomes are in equator ( chromosome seen by light microscope). 4. Anaphase: centromeres separate separation of chromatids that migrate toward poles.
5. 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).
Meiosis: Meiosis: 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).
At 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.
During 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.
Meiosis II: result in two daughter cells each of them containing haploid 23 single structured chromosome number with half amount 1/2 of DNA.
Cytodifferentiation These are cellular changes during gametogenesis: This comes after meiotic divisions.
