Gametogenesis: Conversion of Germ Cell PDF

GAMETOGENESIS: Conversion of Germ Cell Chromosome Theory of Inheritance into Male and Female (Sex Cells) Traits of a new individual are determined by specific genes on chromosomes inherited from The production...

GAMETOGENESIS: Conversion of Germ Cell Chromosome Theory of Inheritance into Male and Female (Sex Cells) Traits of a new individual are determined by specific genes on chromosomes inherited from The production of gametes from haploid the father and the mother. precursor cells. Humans have approx. 23,000 genes on 46 initial of chromosomes (diploid) → 23 pairs from parents →a germ cell undergoes meiosis to produce Genes on the same chromosomes tend to be cells which directly develop into gametes. inherited together and so are known as linked genes. In somatic cells (body cells), each chromosome pair is homologous (same/similar), one coming from the female gamete, → once they reach developing gonads one from the male gamete. (testis/ovaries) 22 of the human chromosomes are autosomes →reproductive organ (body cells), while one pair is the sex in an individual during gestation (embryonic chromosomes (X and Y chromosome) = 23 development) they will called as spermatogonium and oogonium→not matured Sex Determination sperm cells and egg cells → are matured! Sex determination results in the development of an individual with characteristics that can Primordial Germ Cells identify them either as male or female, and Gametes are derived from Primordial Germ sometimes hermaphrodite. Cells (PGCs) that are formed in the epiblast during the 2nd weeks of embryonic development and more to the wall of the yolk sac. At (the beginning of) 4th week, these PGCs migrate towards the developing gonads, arriving at the end of the 5th week. Epiblast Gives rise to all 3 germ layers (endoderm, → SRY gene present in Y chromosome is now /. mesoderm, , known as master regulator of the sex. ectoderm) determination. and the primordial cells. → these SRY genes bind to other DNA causing alteration of DNA leads to expression of a Clinical Correlates: number of genes leading to the formation of Teratoma testis. Tumors that contain a variety of tissues such as bones, muscles, hair, gut epithelia, etc. Primary Sex Determination May have arise from pluripotent stem cells SRY Gene (diff type of cells) – Sex-determining region of the Y chromosome Evidences suggests that teratomas arise from – Codes for the protein testis-determining factor PCGs strayed from migratory paths, or (TDF) epiblast cells (3 germ layers) during – Transforms bipotential gonad into a testis gastrulation. → happens during 7th week of development, these SRY genes starts to produce protein TDF Y chromosome considered as gene poor, means low genes located here. However, by the presence of the SRY gene it is sufficient to cause the development of male organs. Bipotential to Specific Gonads S Phase 2 precursor organs: DNA synthesis 1. Wolffian duct – differentiates into the Chromosomes in DNA replication is visible in structure of the male genital tract prophase →during 3rd month of gestation, XY DNA replicates in order for daughter cells to fetuses (sertoli cells) secrete mullerian inhibiting have identical sets of copies as the mother cell. hormone During this phase, it checks the DNA if there's Müllerian inhibiting hormone - causes the an error in replication, if there is an error the cell Müllerian ducts to atrophy (shrink) instead of division stops leading to cell defects. developing into the oviducts and uterus 2. Müllerian duct – source of the female reproductive organs → if the fetal gonads do not secrete testosterone in time, even if it is XY fetus, the outcome will be XX. →however, the sexual differentiation is not yet complete (maturation) until it reached developmental stage (puberty) → Prophase - chromosomes starts to condense making them visible under microscope Prometaphase (Late prophase or before metaphase) - centrioles forming their spindle and starts to capture the chromosomes → Metaphase - chromosomes start to align in the middle, and check if the chromosomes are attached to the spindle particularly in the centromere. → Anaphase - separation of chromosomes Cytokinesis - formation of cleavage → Telophase - forming 2 identical daughter cells Meiosis Cell division that takes place in gametes to generate male and female gametes. Mitosis Requires two divisions to reduce the number of The division of one somatic cell giving rise to chromosomes by half, producing haploid two identical daughter cells. daughter cells. Each daughter cell receives the complete → Meiosis I complement of 46 chromosomes. → Meiosis II Before mitosis, each chromosome replicates its DNA.  DNA Replication Synapsis - 2 homologous chromosomes pair up Crossing-Over (Meiosis I - Prophase I) – Chiasma In humans, at the end of meiosis I, each daughter cell will only have 23 unique chromosomes (haploid) –EACH HOMOLOGOUS CHROMOSOMES COMPOSED OF 2 SISTER CHROMATIDS. –1 PAIR HOMOLOGOUS CHROMOSOMES COMPOSED OF 4 SISTER CHROMATIDS. Mitosis - 1 mother cells will give rise to 2 identical daughter cells Meiosis - 1 mother cells will give rise to 4 non-identical daughter cells (haploid cells)