Textbook notes-Chapter 26

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Biological Sciences
Course Code
Ingrid L.Stefanovic

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Chapter 26 Puberty: The period when a person makes the transition from being non-reproductive to being reproductive Pseudohermaphroditism: males having underdeveloped male external sex organs through a gene causing deficiency in one of the male hormones (DHT); develop some but not all male characteristics N Humans are sexually dimorphic in that males and females are physically distinct Sex Determination The male and female sex organs consist of three sets of structures: N gonads: organs that produce gametes -male gonads are the testes that produce sperm -female gonads are the ovaries that produce eggs -male and female gonadal cells are undifferentiated as germ cells before differentiating N internal genitalia: consists of accessory glands and ducts that connect gonads with outside environment N external genitalia : external reproductive structures Other than the eggs and sperm, each nucleated cell contains 46 chromosomes in which 22 pairs are autosomes (human body form) and one pair of sex chromosomes (sex organs) The Sex Chromosomes Determine Genetic Sex N Males inherit a Y chromosome from their father and an X chromosome from their mother N The presence or absence of a Y chromosome determines whether one is a female or male N Absence of an X chromosome causes death in a zygote because of essential genes @L[ZZL}K9female has XO chromosome bu}ZL[L2}L}KoKo reproductive functioning N Once ovaries develop, one X chromosome inactivates and become nuclear chromatin called Barr body Sexual Differentiation Occur in the Second Month of Development (refer to Figure 26.3) N Before the seventh week of development, the embryo tissues are considered bipotential because they are neither male or female N Bipotential internal genitalia consists of two pairs of accessory ducts called the Wolffian duct and the Mullerian duct N As development proceeds, one pair of ducts develops while the other degenerates www.notesolution.com N The bipotential external genitalia consist of a genital tubercle, urethral folds, urethral groove, labioscrotal swellings (Figure 23.6b) N Gender determination depends on the presence or absence of the SRY gene on the Y chromosome (absence of the gene, gonads develop into ovaries) Male Embryonic Development (refer to Figure 26.4) N SRY gene activates additional genes that cause the gonadal medulla to develop into testes ~Z}Z}L]ZL[t necessary; develops after testes are formed) N The testes secrete three hormones that influence development of internal and external genitalia -Sertoli cells secrete anti-Mllerian hormone (AMH): Mullerian ducts regress -Leydig cells secrtete testosterone and DHT: internal and external sex organ development N Testosterone also controls migration of the testes from the abdomen into the scrotum Female Embryonic Development N Female embryos have no SRY gene, so the gonadal cortex develops into ovarian tissue N Absence of AMH causes the Mullerian ducts to develop into the vagina, uterus, and Fallopian tubes N Wolffian ducts degenerate and external genitalia take on female characteristics Basic Patterns of Reproduction Eggs are the largest cells in the body and are non-motile; move through reproductive tract by smooth muscle contraction and cilia Sperm are small and the only flagellated cells in the body, making them motile Gametogenesis: gamete production (timing is different between males and females) N Women are born will all the oocytes(eggs) they will ever have; eggs are released once per month for 40 years until ceasing (menopause) N Men manufacture sperm continuously from when they reach reproductive maturity; sperm production diminishes with age but d}ZL[ Z Gametogenesis begins in Utero and Resume During Puberty (refer to Figure 26.5) N JZLK]}Z]Z2]LZ7Z oo[Z-o] Z} ]oLo] chromosomes N In the first meiotic division, the duplicated chromosomes remain paired as sister chromatids so each secondary gamete contains 23 doubled chromosome N After the second meiotic divison, secondary gametes divide and each gamete results in two cells that have 23 single chromosomes Male Gametogenesis At birth, the testes have not progressed beyond the mitosis stage and contain immature germ cells (spermatogonia) www.notesolution.com
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