Embryology
Wednesday, 2nd March 2022
Intro to Embryology:
Embryology is the process of the
development of an organism from
the single fertilised ovum to a fully
formed organism.
The Carnegie Stages are
specifically designed for human
development.
Embryonic development
involves cell division, cell
migration, cell shape change,
cell differentiation and cell
death (apoptosis).
The embryo begins with fertilisation
with the merging of the sperm and
the ovum.
Gametes are formed via
gametogenesis.
Gametogenesis:
In males it occurs in the testes, while in females it forms in the ovaries.
Primordial germ cells differentiate to form sex cells.
The main steps in mitosis include:
1. Increase in the number of germ cells via mitosis.
2. Undergo meiosis to decrease the number of chromosomes in the germ cells
from 2n to n in the gametes.
Embryology 1
, 3. Finally, there is the structural and functional change of these haploid pre-
cells into sperm and egg cells.
Mitosis versus Meiosis:
Both begin with a cell with 23 pairs
of chromosomes (46 in total) from
the maternal and paternal sides
making it diploid.
The chromosomes replicate during
interphase to form two sister
chromatids (identical) joined by a
centromere.
A total of 92 chromatids.
During mitosis these sister
chromatid are split apart and
separate into two new cells.
In meiosis, reductive divisions
occurs to produce four gametic
cells which are all haploid.
Occurs in meiosis I and II.
Embryology 2
, Mitosis vs meiosis.
Crossing over occurs in prophase during meiosis I.
A synapses occurs between the two pairs and provides genetic variation in
your gametes.
Chiasmata form at these places of crossing over.
This leads to many different possibilities of genetic variation.
Independent assortment of the
chromosomes during division in
meiosis leads to genetic variation
and a total of over eight million
different potential combinations.
The entire purpose of crossing
over and assortment is to
increase variation in the
population to make it more
adapted to its environment.
Embryology 3
Wednesday, 2nd March 2022
Intro to Embryology:
Embryology is the process of the
development of an organism from
the single fertilised ovum to a fully
formed organism.
The Carnegie Stages are
specifically designed for human
development.
Embryonic development
involves cell division, cell
migration, cell shape change,
cell differentiation and cell
death (apoptosis).
The embryo begins with fertilisation
with the merging of the sperm and
the ovum.
Gametes are formed via
gametogenesis.
Gametogenesis:
In males it occurs in the testes, while in females it forms in the ovaries.
Primordial germ cells differentiate to form sex cells.
The main steps in mitosis include:
1. Increase in the number of germ cells via mitosis.
2. Undergo meiosis to decrease the number of chromosomes in the germ cells
from 2n to n in the gametes.
Embryology 1
, 3. Finally, there is the structural and functional change of these haploid pre-
cells into sperm and egg cells.
Mitosis versus Meiosis:
Both begin with a cell with 23 pairs
of chromosomes (46 in total) from
the maternal and paternal sides
making it diploid.
The chromosomes replicate during
interphase to form two sister
chromatids (identical) joined by a
centromere.
A total of 92 chromatids.
During mitosis these sister
chromatid are split apart and
separate into two new cells.
In meiosis, reductive divisions
occurs to produce four gametic
cells which are all haploid.
Occurs in meiosis I and II.
Embryology 2
, Mitosis vs meiosis.
Crossing over occurs in prophase during meiosis I.
A synapses occurs between the two pairs and provides genetic variation in
your gametes.
Chiasmata form at these places of crossing over.
This leads to many different possibilities of genetic variation.
Independent assortment of the
chromosomes during division in
meiosis leads to genetic variation
and a total of over eight million
different potential combinations.
The entire purpose of crossing
over and assortment is to
increase variation in the
population to make it more
adapted to its environment.
Embryology 3
