Sex Determination and Development Flashcards by Brianna Tang

Differentiate the terms sex, gender, and sexuality

Sex = what a person has (morphological sex/gonads)
Gender = who a person identifies as
Sexuality = who a person likes/loves

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What are the components of sex

Morphological sex = what is visible (external genitalia)
Primary sex characteristics: changes to the sexual organs themselves (uterus, vagina, penis, and testes)
Secondary sex characteristics: other visible changes that mark adult maturation such as changes in height and body shape
Gonads = reproductive organs (testes or ovaries)

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Give some examples of primary sex characteristics (male/female)

production of gametes
growth of reproductive organs

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Give some examples of secondary sex characteristics (male/female)

growth of pubic hair
facial hair
voice deepening for men
breast development
hips widening

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What are gonads

male = testes -> produces smaller gametes (sperm)
female = ovaries -> produces larger gametes (eggs)

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What are intersex characteristics

Sex is not a binary property
- characteristics can fall between the common ranges for male and female
- conditions for Diverse Sexual Development (DSD) are another term used for intersex conditions
- characteristics that lie somewhere between the male and female sex

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Differentiate morphological sex from chromosomal sex

Morphological sex refers to what is visible (may be external reproductive organs)

Chromosomal sex refers to the sex chromosomes present in the somatic cells

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What is chromosomal sex

Sex defined by the sex chromosomes present in somatic (non-germline) cells

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What is the combination for male chromosomal sex

XY
- only males have a Y chromosome

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What is the combination for female chromosomal sex

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How many pairs of autosomes do humans carry

Humans have 22 pairs of autosomes and normally 1 pair of sex chromosomes in diploid cells

Diploid = contains two sets of chromosomes (somatic cells)
Haploid = contain one set of chromosomes (gametes)

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Is the Y or X chromosome primarily responsible for determining sex

Sex is primarily determined by the Y chromosome
- most individuals will have an X chromosome, but the primary sex characteristics are determined by the presence of the Y chromosome
- if the Y chromosome is present, it sets the development for gonadal sex (male genitalia/gonads)

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What gene is responsible for initiating the cascade of male-typical sex development

SRY

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What is the role of SRY and where can it be found

SRY is a gene on the Y-chromosome
- responsible for initiating the cascade of male-typical sex development
- this gene transcribes/activates other genes/proteins that drive the development of other male sex characteristics

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What happens when SRY is mutated/changed

This is most evident in DSDs where the critical role of SRY becomes prevalent

when specific changes occur to SRY, this can cause DSDs

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Explain what is expressed in each of the following scenarios:

Female = XX

Male = XY

Female = XY
- XY female with SRY gene missing

Male
- XX male with SRY

Female = XX
- expresses characteristics of a female

Male = XY
- expresses characteristics of a male

Female = XY
- XY female with SRY gene missing
- female sex development because the Y chromosome has some kind of mutation that causes the SRY gene to be missing
- even though the person has a Y chromosome, they will not express male characteristics because the SRY gene is missing

Male
- XX male with SRY
- X chromosome expresses SRY because of some mixing up that occurred during meiosis (gamete formation)
- develops male characteristics even though they have XX chromosomes

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What is gonadal sex

Defined by the anatomy of the gonad, which determines which type of gametes are produced
- either sperm or eggs

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How does gonadal sex differ from morphological sex and chromosomal sex

Gonadal sex refers to the anatomy of the gonads and type of gametes produced

Morphological sex refers to the external genitalia? and physical characteristcs (what is visible)

Chromosomal sex refers to the combination of sex chromosomes in somatic cells (and SRY gene)

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What are the two types of gonads and their respective gametes produced

Testes
- produces sperm
- smaller gametes
Ovaries
- produces ova (eggs)
- larger gametes

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All embyros have two undifferentiated gonads and two sets of internal ducts at early developmental stages:

What is this stage called

the INDIFFERENT stage

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What is the name of the two ducts that all embryos have during the indifferent stage

Woffian duct
Mullerian duct

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Define what bipotential gonad means

Because embyros start in the indifferent stage where they hae two undifferentiated gonads and two sets of internal ducts, they are considered bipotential
- they have the potential to develop into testes or ovaries
- based on the presence or absence of SRY gene

All mature gonads have three functional cell classes even though they differ in their exact physiological and anatomical properties: What are these three functional cell classes

Steroid-secreting cells
Support “nurse” cells
Germ cells

What are steroid-secreting cells

responsible for the secretion of steroid hormones

in females = estrogen
in males = testosterone

What are support "nurse" cells

What are germ cells

sex cells (eggs and sperm) that sexually reproducing organisms use to pass on their genomes from one generation to the next in females = oocyte in males = spermatogonia

Differentiate SRY- and SRY+

SRY- = without SRY, ovarian determining genes are expressed = ovaries SRY+ = with SRY, initiates cascade which leads to the expression of testes determining factors = testes

What is SOX9

A testes determining factor - activation of SOX9 occurs when the SRY gene is present - regulates the development of other male genes

The three functional classes of cells in gonads have different names in both ovaries and testes: What are they called in testes

Support cells = Sertoli cells Steroid-secreting cells = Leydig cells Germ cells = spermatogonia

The three functional classes of cells in gonads have different names in both ovaries and testes: What are they called in ovaries

Support cells = granulosa Steroid-secreting cells = follicular cells (granulosa and germ cells) Germ cells = oocyte

What is the role of anti-Mullerian hormone (AMH) in the testes

Support cells in the testes (Sertoli cells) secrete anti-Mullerian hormone (AMH) which leads to the male typical development of ducts

Describe the difference between AMH+ and AMH-

From a bipotential gonad/indifferent stage: AMH+ = AMH degrades Mullerian ducts = Wolffian ducts develop forming male internal genitalia AMH- = no AMH produced = Mullerian ducts develop and form female internal genitalia (oviduct/Fallopian tubes) = Wolffian ducts degrade

During male gonadal development, which duct degrades During female gonadal development, which duct degrades

Male = Mullerian ducts degrade Female = Wolffian ducts degrade

Which of the following embryonic structures eventually forms the uterus 1. Genital ridge 2. Wolffian duct 3. Mullerian duct 4. Hindgut

Uterus = female reproductive organ ANSWER: Mullerian duct

Differentiate the role of steroid-secreting cells in the ovaries and testes

XX = ovaries = follicular cells (granulosa and germ cells) = secretes mostly estrogen (androgen/progesterone) XY = testes = Leydig cells (Sertoli and germ cells) = secretes mostly testosterone (androgen)

Recall: What are steroid hormones

Class 3 lipid derivatives - derivative of cholesterol - hydrophobic - lipid-soluble

What are the five classes of steroid hormones receptors

1. Mineralcorticoids (MR) 2. Glucocorticoids (GR) 3. Estrogens (ER) 4. Androgens (AR) 5. Progesterone (PR)

True or False: All hormones are precursors to another hormone

FALSE - only SOME hormones are precursors to other hormones

True or False: Converting enzymes can be found in non-endocrine tissues

TRUE - converting enzymes can be expressed in other tissues that are non-endocrine

True or False: All steroid hormone reactions are irreversible

FALSE - NOT ALL, but many reactions are irreversible - only go in one direction

Which cells would you expect to express the enzyme 17B-HSD if this enzyme produces androgens

1. Leydig cells in the testes 2. Follicular cells in the ovary

Which cells would you expect to express the enzyme 21-hydroxylase if this enzyme produces glucocorticoids/mineralocorticoids

1. Zona fasciculata cells in the adrenal cortex - produce glucocorticoids (cortisol) - from adrenal cortex

What is morphological/anatomical sex

Defined by the anatomy of the external genitalia - which develop in response to androgen receptor signalling

When do external genitalia begin to develop

at 9 weeks of fetal development

How does female external genitalia development differ from male external genitalia development

Leydig cels in testes produce testosterone and dihydrotestosterone which cause the development of male external genitalia Meanwhile, follicular cells in ovaries do not produce gonadal steroids, which is what causes the female external genitalia to develop

Sex hormones can also be found outside the reproductive system - Name another place it can be found

Within parts of the brain - key receptors for both ER and AR expression are subnuclei within the hypothalamus and amygdala

What is the enzyme aromatase

Converts androgens to estrogens

During puberty, gonadal hormone levels rise in both sexes, initiating processes of sexual maturation - secretions of which hormone from the hypothalamus is increased

hypothalamus increases GnRH production - FSH => gamete production initiated - LH => sex hormones are released, initiating secondary sex characteristics and behaviour

What causes the development of secondary sex characteristics

Elevated levels of testicular or ovarian hormones

Describe some secondary sex characteristics in males caused by elevated levels of testosterone

- body hair growth - bone growth - myofibre hypertrophy - activational effects on sex drive and sexual behaviours - increased RBC production - growth of larynx and vocal cords - development of accessory structures and sperm production

Describe some secondary sex characteristics in females caused by elevated levels of estrogen

- body hair growth - development of mammary glands (breast tissue) - bone growth - some myofibre hypertrophy - activational effects on sex drive and sexual behaviours - reduced blood cholesterol levels - development of uterine lining (period) and accessory reproductive structures

Which hormone is the main testicular secretion

Testosterone

Which hormone is the main ovarian secretion

Estrogen