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Chapter 6 - Matters of Sex

Section 1 - Our Sexual Selves

Development of Sex

  • Sex can be considered at chromosomal, gonadal, phenotypic, and gender identity levels.
  • Sexes look alike until the ninth week of development then an unspecialized gonad develops either into testes or ovaries
  • The mullerian ducts develop into females
  • Wolffian ducts develop into male
  • Females are often considered a default option

Sex Chromosomes

  • Human females are homogametic (XX) females produce only X and males are heterogametic (XY) they produce X and Y
  • (In birds and snakes males are ZZ and females are ZW)
  • The Y chromosome contains few identified genes,
  • X chromosome contains more than 1,500 genes. And they possibly crossover with the other X
  • Pseudoautosomal regions at both tips of the Y chromosome contain genes that have counterparts on the X

Sex-Linked Traits

  • Sex-Linked traits are traits where the genes are located on one of the sex chromosomes.
  • X-linked recessive traits pass from carrier (mother) to son 50% of the time
  • There is no possibility of transmission from father to son
  • 100% transmission from father to daughter

Sex-Linked Traits

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The Y Chromosomes

The Y Chromosome

  • The bulk of the Y chromosome is the MSY (male-specific region)
  • This lies between the two autosomal regions
  • It is full of palindrome-ridden region called amplicons.
  • The male determining gene, SRY, has been found on the Y chromosome.
  • The SRY gene is a single copy gene unique to the Y chromosome.
  • The SRY protein called transcription factor initiates development of male features and suppressing development of female features.

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Male Factors

  • Factors necessary for male development include Anti-Müllerian Hormone, testosterone, development of male structures epididymis, vas deferentia, seminal vesicles, dihydrotestosterone (DHT). urethra, prostrate gland penis and scrotum
  • In the absence of these male factors, the embryo follows the female developmental pathway.
  • Androgen insensitivity syndrome: absence of receptors for testosterone stops cell in early reproduction
  • XY develops as a female

Abnormal Conditions

  • Pseudohermaphrodites (Intersex) are chromosomally one sex, but look phenotypically like the other sex.
  • Testes present indicate the SRY gene is functioning
  • Block in testosterone prevents the fetus from developing male structures.
  • Masculinization may begin at puberty when the adrenal gland produces testosterone.
  • Congenital adrenal hyperplasia produces excess testosterone causing overgrowth of penis or clitoris

Abnormal Conditions

Sexual & Gender Identity

  • Gender Identity – Is Homosexuality Inherited?
  • There is no one single “gay” gene but there could me many genes involved.
  • But strong evidence that supports it may be epigenetic.
  • Reflects many genes & environmental factors

Sexual & Gender Identify

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