Lecture 20 - Sex Determination and Development

Question 1

What are the 6 biological classifications of sex?

Answer 1

Morphological sex, secondary, primary, gonads, sex hormones, chromosomes/gene

Question 2

Is sex binary?

Answer 2

NO!! There are intersex (aka Diverse Sexual Development) peeps (sex characteristics that fall between “male” and “female”)

Question 3

Chromosomal sex

Answer 3

Sex chromosomes present in somatic (non-germ line) cells

ie. XY (male) and XX (female)

Question 4

Gene that is responsible for initiating male typical sex development

Answer 4

SRY gene

Question 5

Gonadal sex

Answer 5

Anatomy of the gonad which determines which type of gametes are produced (ie. sperm or eggs)

Question 6

What are the 2 sets of internal ducts during early developmental stages?

Answer 6

Wolffian duct and Mullerian duct

Question 7

What are the 3 functional cell classes in mature gonads?

Answer 7

1. Steroid secreting cells
2. Support (nurse) cell
3. Germ cells

Question 8

True or False? At early developmental stages, all embryos will already be determined which gonad they will develop, therefore, will only have 1 set of internal duct

Answer 8

False - at early stages of developmental stages, all embryos have 2 undifferentiated gonads and 2 sets of internal ducts

Question 9

Presence of SRY gene

Answer 9

Will determine whether the gonad will develop into a testis or ovary by expressing testes-determining factors

XY -> SRY+ -> testes determining factor (TDF, SOX9+) -> testes

Without SRY, ovarian-determining genes are expressed

Question 10

What do the sertoli cells secrete?

Answer 10

They are support cells in the testes that secrete Anti-Mullerian Hormone (AMH), leading to male typical development of ducts

Question 11

How is estrogen secreted from the ovaries?

Answer 11

Ovaries —> Follicular cells (steroid secreting cells) and granulosa and germ cells —> mostly estrogen

Question 12

How is testosterone secreted from the testes?

Answer 12

Testes—>Leydig cells (steroid secreting cells) —> mostly testosterone

Question 13

Key points of the production of steroid hormones

Answer 13

1. 5 classes of steroid hormone receptors
2. Some hormones are precursors to other hormones
3. Converting enzymes can be found in non-endocrine tissues
4. Many reactions are irreversible

Question 14

Morphological sex

Answer 14

The anatomy of the external genitalia which develop in response to androgen receptor signalling

Question 15

When androgen is present, how is the male external genitalia formed?

Answer 15

Testes —> Leydig cells —> testosterone —> dihydrotestosterone —> male external genitalia

Question 16

Process of sexual maturation during puberty

Answer 16

Hypothalamus increases GnRH production, which produce the gonadal hormones:

FSH —> gamete production initiated
LH —> sex hormones are released; initiating secondary sex characteristics and behaviour

Question 17

What are examples of secondary sexual characteristics of testosterone?

Answer 17

• Body hair
• Bone growth - and then closure of epiphyseal plates
• Myofibre hypertrophy
• Activational effects on sex drive and sexual behaviours
• Increased red blood cell production
• Growth of larynx
• Development of accessory structures and sperm production

Question 18

What are examples of secondary sexual characteristics of estrogen?

Answer 18

• Mammary glands
• Bone growth - rapid closure of epiphyseal plates
• Some myofibre hypertrophy
• Activational effects on sex drive and sexual behaviours
• Reduced blood cholesterol levels
• Development of uterine lining and accessory reproduction structures

Question 19

True or False. Some effects of the steroid hormones on secondary sex characteristics are reversible, some are not.

Answer 19

True