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Gentics Ch6 - Sect1 Notes
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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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