1. Matters of Sex Chapter 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

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

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

7. How was SRY discovered?
XY female
XX male

8. 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

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

10. Partial map of Y PAR1 SRY Non-recombinant region Sperm development AZF

11. Nonrecombinant Region: Center of chromosome & majority of chromosome
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

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

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

14. 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

15. 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

16. 6.2: Traits Inherited on Sex Chromosomes
Y-linked: genes on the Y chromosome
RARE-few genes on this chromosome
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.

18. 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

19. In a man’s family there is a history of deafness
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.

20. Duchenne Muscular Dystrophy (DMD) is a sex-linked disease
Duchenne Muscular Dystrophy (DMD) is a sex-linked disease. Neither of Rachel’s parents are affected by the disease, nor is she or her sisters. 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?

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

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

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

25. Muscular Dystrophy Duchene Muscular Dystrophy
Progressive muscle weakness

26. X-linked dominant traits
Caused by a dominant allele on the X-chromosome
Often can be have a more pronounced affect on males
Sometimes causing death before birth
Father passes trait to daughters

27. X-linked Dominant Disorders

28. What about this scenario…
A father has a dominantly inherited trait on the X- chromosome. He marries a woman who also has the trait but her mother did not. What is the probability that their daughters will inherit this trait? Their sons?

29. Examples Incontinentia pigmenti Swirls of pigment on the son
Pleiotropic: also causes hair loss, visual problems, missing and peg shaped teeth, seizures
Deadly in males

30. Congenital Generalized Hypertrichosis (CGH)
Increased hair growth
More dramatic in males due to hormones

31. X-inactivation Only need 1 X chromosome…right guys!?
What do women do with 2??
We only use one at a time
Turn off one of the X’s

32. X-inactivation

34. Sex-limited traits
Affects a structure or function of the body that is only present in males or infemales.
Beard growth in humans
If Albus had a daughter would
she also have a beard like his?

35. Sex-limited traits
Cattle

36. Sex-influenced traits
An allele is dominant in one sex but recessive in another
Could be X-linked or autosomal
Was Tom Riddle’s mother also bald if
he inherited the allele from her?
Dominant in males, but recessive
in females

37. Genomic Imprinting “Parent of origin” effect Methylation: CH3