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Matters of Sex Chapter 6

Matters of Sex Chapter 6. We all start out the same…. From 0-9 weeks of development, both sexes look the same During 5 th week, unspecified gonads develop Form near two sets of ducts Muellerian ducts: develop in females, degenerate in males Wollfian ducts: develop in males

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Matters of Sex Chapter 6

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  1. Matters of SexChapter 6

  2. We all start out the same… • From 0-9 weeks of development, both sexes look the same • During 5th week, unspecified gonads develop • Form near two sets of ducts • Muellerian ducts: develop in females, degenerate in males • Wollfian ducts: develop in males degenerate in females

  3. Choice is made during week 6 • Governed by the chromosomes • Sex chromosomes in humans are different depending on the sex. • Male: • Female:

  4. Y-chromosome • SRY: Sex determining region of the Y chromosome • When this is activated, hormones are produced that lead toward male development

  5. How was SRY discovered? • XY female • XX male

  6. Sex chromsomes • Heterogametic- having different sex chromosomes • Homogametic- having the same sex chromosomes • Not the same in all species: • Birds: Males are ZZ, Females are ZW

  7. Human chromosomes • X: over 1000 identified genes • Y: 85 protein encoding genes • Mapping the chromosomes… • Does Y ever cross over?

  8. Partial map of Y PAR1 SRY Non-recombinant region Sperm development AZF PAR 2

  9. Nonrecombinant Region: Center of chromosome & majority of chromosome. Does not go through crossing over • Pseudoautosomal Regions (PAR1&2): At the very ends of the chromosomes, have counterparts on X, can cross over. • X-Y homologs: similar to genes on X but not exactly the same, in the nonrecombinant region. • Indicate possible evolutionary background, Y could be a stripped-down, ancestral X chromosome

  10. Phenotype Forms SRY gene codes for transcription factors Transcription factors turn on genes to produce anti-Mullerian hormone Male Sexual Development There are some genetic abnormalities which can interfere with this process…

  11. Androgen Insensitivity Syndrome • Mutation in a gene on X chromosome • No receptors for testosterone in early reproductive development • Does not develop as a male

  12. Pseudohermaphroditism • Testes are present • Anti Mullerian hormone produced • HOWEVER…block in testosterone synthesis so male structures do not develop • Child appears to be a girl • At puberty, adrenal gland begins producing testosterone leading to masculinization • Voice deepens, breast do not develop, menstruation does not begin, clitoris may enlarge greatly to look like a penis • “Guevedoces”- Dominican Republic

  13. Does Gender identity Have a Genetic Cause? The evidence says, perhaps, at least in part… • Homosexuality is seen in all cultures and has been observed for thousands of years. • Seems to have some genetic link if looking at identical twins • More likely to both be homosexual than a brother and sister pair • Some DNA sequences appear more commonly in homosexual individuals • Lowered brain serotonin linked with homosexual behavior in animals

  14. 6.2: Traits Inherited on Sex Chromosomes • Y-linked: genes on the Y chromsome • RARE-few genes on this chromsome • Passed from male to male • Infertility, none other clearly defined • X-linked: genes on X chromosome • Different expression in males and females • In females they work like any autosomal trait (females have 2) • In males, one recessive allele causes the trait, making recessive traits more common in males than females.

  15. Criteria for X-linked Recessive trait • Always expressed in the male • Expressed in a female homozygote but not heterozygote • Passed from homozygote or heterozygote mother to affected son • Affected female has an affected father and a mother who is affected or a heterozygote

  16. In a man’s family there is a history of deafness. This specific type is a recessive sex-linked disorder. This man has this specific type of deafness and wants to know the risk of passing it on to his children. His wife does not know whether or not she is a carrier. The couple gives birth to twins, a girl and a boy. The girl is deaf, but the boy is not. Show a cross of this couple and how this could have occurred.

  17. Duchenne Muscular Dystrophy (DMD) is a sex-linked disease. Neither of Rachel’s parents are affected by the disease, nor are her sisters or her. They assumed that the disease which had run in their family before was not present in their immediate family. When Rachel’s mother gives birth to a son, they are surprised to find out that he has DMD. How could this have happened?

  18. Examples: • Colorblindness • Ishihara Test • X-linked recessive, more common in males • 80% of individuals have soecific orange/red colorblindness • Another common type is red/green colorblindness

  19. A man who is colorblind marries a woman who is not colorblind but her father was colorblind… • Phenotypic ratio?

  20. Hemophilia • “The bleeder’s disease” • Prevents proper blood clotting • Affecting the European royal families

  21. Muscular Dystrophy • Duchene Muscular Dystrophy • Progressive muscle weakness

  22. X-linked Dominant Disorders

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