Embryology CLASS I INTRODUCTION MITOSIS MEIOSIS Child birth
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 (2 n) 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
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