Q20 - Sex Determination

Question 1

What is the developmental rate hypothesis in temperature dependant sex determination in reptiles?

Answer 1

This is due to rate of embryonic development rather than directly related to temperature

Question 2

What is the hormone hypothesis in temperature dependant sex determination in reptiles?

Answer 2

The presence of sex hormones, controlled by an unknown temperature dependent mechanism, determines sex

Question 3

What evidence is there to support the developmental rate hypothesis in temperature dependant sex determination in reptiles?

Answer 3

Early studies in crocodilians found that sex was more closely related to developmental rate in the first half of incubation rather than temperature

Question 4

What is the issue with the evidence supporting the developmental rate hypothesis?

Answer 4

All evidence comes from early studies and more recent studies produced conflicting results

Question 5

What is thought to be the driving factor in the hormone hypothesis?

Answer 5

Aromatase - manipulation can influence offspring sex

Question 6

What did Sun et al. do?

Answer 6

Used T3 thyroid hormone to test both hypotheses at once as it influences developmental rate and gonadal sex

Question 7

How would Sun et al. know which hypothesis was favoured?

Answer 7

The ratio of males to females

• If the developmental rate hypothesis was true, there would be more females
• If the hormone hypothesis was true, there would be more males

Question 8

What did Sun et al. find?

Answer 8

T3 exposure produced more males, meaning the hormone hypothesis was favoured