GAMETOGENESIS
Gametogenesis:
Is aprocess of gamet formation =Ova or sperm formation
Conversion of Diploid Germ Cells into Haploid Male and Female Gametes
a process of formation and maturation of the gametes (sperm and ovum)
involves
Mitosis
meiosis and
cytodifferentiation.
1.Mitosis
Mitosis
is the process by which one cell divides into two genetically identical daughter
cells.
Each daughter cell has 46 chromosomes (full human complement).-diploid
Before mitosis, each chromosome replicates its DNA.
Chromosomes are diffuse and unrecognizable under a light microscope.
2. Meiosis
Meiosis
is the specialized cell division in germ cells that produces male and female
gametes (sperm and egg).
Reduce the chromosome number from diploid (46) to haploid (23).
Meiosis involves two consecutive divisions: Meiosis I and Meiosis II
Before meiosis I, germ cells (spermatocytes and primary oocytes) replicate
their DNA.
Each of the 46 chromosomes becomes two sister chromatids.
Meiosis I
Homologous chromosomes pair up (synapsis).
, The pairing is point-for-point exact, except XY chromosomes.
Homologous pairs then separate, producing two haploid daughter cells.
Chromosome number reduced: Diploid → Haploid
Crossing over occured
Meiosis II
Sister chromatids in each haploid cell are separated.
Result: Each gamete contains 23 chromosomes (haploid).
Crossover (Genetic Recombination)
Occurs during meiosis I.
Is exchange of chromatid segments between paired homologous
chromosomes.
Segments of chromatids break and swap.
Points of interchange temporarily form an X-shaped structure called a
chiasma
Frequency: ~30–40 crossovers per meiotic I division (1–2 per
chromosome).
More frequent between genes that are far apart on a chromosome.
Significance of Meiosis
Genetic variability: Crossover redistributes genetic material.
Random distribution of homologous chromosomes to daughter cells.
Haploid gametes ensure that fertilization restores the diploid number (46
chromosomes).
3. cytodifferentiation
is the process by which unspecialized cells (like primordial germ cells or
embryonic cells) become specialized in structure and function
Maturation complates
The Purpose of Gametogenesis –
Production of gametes –
Reduction of the number of chromosomes by half. –
Alteration of the shape of germ cells for fertilization
Gametogenesis:
Is aprocess of gamet formation =Ova or sperm formation
Conversion of Diploid Germ Cells into Haploid Male and Female Gametes
a process of formation and maturation of the gametes (sperm and ovum)
involves
Mitosis
meiosis and
cytodifferentiation.
1.Mitosis
Mitosis
is the process by which one cell divides into two genetically identical daughter
cells.
Each daughter cell has 46 chromosomes (full human complement).-diploid
Before mitosis, each chromosome replicates its DNA.
Chromosomes are diffuse and unrecognizable under a light microscope.
2. Meiosis
Meiosis
is the specialized cell division in germ cells that produces male and female
gametes (sperm and egg).
Reduce the chromosome number from diploid (46) to haploid (23).
Meiosis involves two consecutive divisions: Meiosis I and Meiosis II
Before meiosis I, germ cells (spermatocytes and primary oocytes) replicate
their DNA.
Each of the 46 chromosomes becomes two sister chromatids.
Meiosis I
Homologous chromosomes pair up (synapsis).
, The pairing is point-for-point exact, except XY chromosomes.
Homologous pairs then separate, producing two haploid daughter cells.
Chromosome number reduced: Diploid → Haploid
Crossing over occured
Meiosis II
Sister chromatids in each haploid cell are separated.
Result: Each gamete contains 23 chromosomes (haploid).
Crossover (Genetic Recombination)
Occurs during meiosis I.
Is exchange of chromatid segments between paired homologous
chromosomes.
Segments of chromatids break and swap.
Points of interchange temporarily form an X-shaped structure called a
chiasma
Frequency: ~30–40 crossovers per meiotic I division (1–2 per
chromosome).
More frequent between genes that are far apart on a chromosome.
Significance of Meiosis
Genetic variability: Crossover redistributes genetic material.
Random distribution of homologous chromosomes to daughter cells.
Haploid gametes ensure that fertilization restores the diploid number (46
chromosomes).
3. cytodifferentiation
is the process by which unspecialized cells (like primordial germ cells or
embryonic cells) become specialized in structure and function
Maturation complates
The Purpose of Gametogenesis –
Production of gametes –
Reduction of the number of chromosomes by half. –
Alteration of the shape of germ cells for fertilization
