Download Embryology *CLASS

Embryology –CLASS -I
• INTRODUCTION
• MITOSIS
• MEIOSIS
Child
birth
The
birth
of a
child,
A new
life.
Embryology is the study of the development of an
embryo (or foetus) from the moment of inception to
the time when it is born as an infant.
Embryo: First 8 weeks of intrauterine life.
Fetus: After embryonic period from third month until
birth.
• The male gonad: Testes.
• The female gonad: Ovary.
• The male gametes: spermatozoa.
• The female gamete: Ovum.
• Gametogenesis involves spermatogenesis and oogenesis.
• The fusion of sperm with a ovum is fertilization and the
result is a zygote.
• D.N.A
• Transfer of characters from parent to child.
• Genes
• Located on chromosomes.
• A typical cell has diploid, 46, chromosomes.
• A gamete has haploid, 23, chromosomes.
• Fertilization restores the diploid number.
• Cell multiplication takes pace by mitosis.
• The resulting cells have same number of chromosomes as
parent cell.
• Occurs in tissues.
• Meiosis is a special type of cell division seen
in gonads, during gametogenesis.
• The daughter cells have reduced number of
chromosomes than parent cell (haploid
number, 23).
• The cell cycle is an
orderly sequence of
events that occurs
from the time when a
cell is first formed
until it divides into
two new cells.
• Most of the cell cycle
is spent in interphase.
• Following interphase,
the mitotic stage of
cell division occurs.
The Cell Cycle
Maintaining the Chromosome
Number
• When a eukaryotic cell is not dividing, the DNA and associated
proteins is a tangled mass of thin threads called chromatin.
• At the time of cell division, the chromatin condenses to form highly
compacted structures called chromosomes.
• Each species has a characteristic number of chromosomes.
• The diploid (2n) number of chromosomes
contains two chromosomes of each kind.
• The haploid (n) number of chromosomes
contains one chromosome of each kind.
• A duplicated chromosome is
made of two sister chromatids
held together in a region called
the centromere.
• Sister chromatids are genetically
identical.
• At the end of mitosis, each
chromosome consists of a single
chromatid.
• During mitosis, the centromeres
divide and then the sister
chromatids separate, becoming
daughter chromosomes.
Mitosis and Meiosis
• Mitosis:
-division of somatic (body) cells
• Meiosis
-division of gametes (sex cells)
Mitosis
• Interphase
• Prophase
• Metaphase
• Anaphase
• Telophase
Interphase
• Interesting things happen!
1. Cell preparing to divide
2. Genetic material doubles
Prophase
Chromosome pair up!
1. Chromosomes thicken and shorten
-become visible
-2 chromatids joined by a centromere
2. Centrioles move to the opposite sides of the
nucleus
3. Nucleolus disappears
4. Nuclear membrane disintegrate.
Metaphase
• Chromosomes meet in the middle!
1. Chromosomes arrange at equator of cell
2. Become attached to spindle fibres by
centromeres
3. Homologous chromosomes do not associate
Anaphase
Chromosomes get pulled apart
1. Spindle fibres contract pulling chromatids to
the opposite poles of the cell
Telophase
Now there are two!
1. Chromosomes uncoil
2. Spindle fibres disintegrate
3. Centrioles replicate
4. Nucleur membrane forms
5. Cell divides
Meiosis
• 4 daughter cells produced
• Each daughter cell has half the chromosomes
of the parent
• 2 sets of cell division involved
Thank you
Dr.Venkatesh G.Kamath