Sheri - Sex Determination

Question 1

What are the four main types of sex determination systems in animals, and how do they differ?

Answer 1

Genetic sex determination (GSD) - Sex is determined by the genes inherited from parent/s, this is found in mammals

Temperature Dependant Sex Determination (TSD) - Sex is determined by the temperature of the egg during its thermosensitive period. This can be found is red-eared slider turtles.

Location Sex Determination - Location-dependent sex determination is a type of environmental sex determination where an organism’s sex is determined by its physical location or habitat during development. This can be seen in Crepidula Snails.

Social Sex Determination -Social sex determination is a type of sex determination where an individual’s sex is influenced by social cues or interactions within a group. This system is found in some fish and invertebrate species. This can be found in species of fish when the male of a group dies.

Question 2

Understand the process of sexual differentiation

Answer 2

Gonad (bi-potential), if there is Sry it trigger the testes development pathway. the precedes of Sox9 activated the Sertoli cell differentiation which releases AMH and then leydig cell (where T is made) differentiation. Genetic regulation and endocrine regulation working together to maintain testes development pathway. AMH is there so the mullerian duct is resorbed and the wolffian duct is retained.
If Sry is absent then ovary development pathway. So granulosa cells differentiate and theca cells differentiate. Those cells produce estradiol from T. Also have genetic regulation and endocrine regulation working together. No AMH so Müllerian duct is retained. Wolffian duct is resorbed

Question 3

Recognize the importance of master sex-determining
genes

Answer 3

In testis, Sry activates Sox9, which drives Sertoli cell
formation and (among other things) Amh secretion. In the absence of Sry it becomes a female.
In mammals, Sry acts at start of pathway triggering
testes development. The gene DMRT1 in males stops them from reverting back to female.
Apart from Sry, most genes involved in sex determination are conserved throughout vertebrates. (this means Sox9, DMRT1, FOXL2)

Question 4

Describe the different types of environmental sex
determination

Answer 4

• Zygotes do not differ genetically
• Determined by environmental factors
  – Temperature dependence
  – Location dependence
  – Social dependence

Question 5

What is sex determination?

Answer 5

• Sex determination is the mechanism by which an
  individual either produced testes (small gametes) or
  ovaries (large gametes)
• In many species, the process relies on sex
  chromosomes (genetic sex determination)
• For example, X and Y