SEX DIFFERENTIATION SPERMATOGENESIS AND OOGENESIS ::
Although the sex characters are apparent at puberty the differentiation occurs from the time when the zygote is formed Zygote is formed after the fertilization (union of spermatozoa the male sex cell with ovum the female sex cell )
Spermatogenesis and Oogenesis ::
Spermatogenesis starts at the puberty under the influence of gonadotrophins secreted from the anterior pituitary gland Germinal epithelial cells of seminiferous tubules undergo first mitotic division and this continues till primary spermatocytes are formed The primary spermatocyte undergoes
first meiotic division to form secondary spermatocyte The total diploid number of chromosomes (44XY i.e.46) of primary spermatocytes are reduced to half (22X or 22Y i.e.23) by the meiotic division hence secondary spermatocyte contains only 23 chromosomes it again undergoes a second maturation meiotic division This is similar to mitotic division and the number of chromosomes remains the same The cells formed are now known as spermatids These are then converted into spermatozoa after maturation
Oogenesis is the formation and maturation of ovum The germinal epithelial cell is differentiated into primary oocyte Primary oocyte undergoes first meiotic division to form one polar body and one secondary oocyte The diploid number of chromosomes in primary oocyte (44XX) are reduced to haploid (half) in first polar body (22X) and secondary oocyte (22X)
Secondary oocyte then enters into second maturation meiotic division to form a mature oocyte (or ovum) and one second polar body The first polar body also undergoes similar maturation meiotic division to form two more polar bodies
Thus the male gamets contain either 22X or 22Y Whereas female gamets contain only 22X if the spermatozoa containing X sex chromosome unites with ovum the two sex chromosomes will be indentical (X and X) and the resulting sex will be a female offspring But if a spermatozoa containing Y sex chromosome unites with ovum the two sex chromosomes will be different (X and Y) and the resulting sex will be a male offspring
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