Sex Determination

Question 1

Heterogametic

Answer 1

With only one X chromosome

Question 2

Homogametic

Answer 2

Two X chromosomes

Question 3

What is the significance of this difference in chromosomes between males and females using this for sex determination?

Answer 3

Being heterogametic can result in sex-linked patterns of inheritance as seen with carrier females and affected males. Sometimes males are unable to mask a trait due to their lack of a second X chromosome.

Question 4

X linked genes

Answer 4

Genes which are found on the part of the X chromosome which is missing in the Y chromosome.

Question 5

Double dosing

Answer 5

Being homogametic means that females have the potential to express genes carried on the X chromosome twice. Despite this, female cells do not have a double dose of gene product from their X chromosomes.

Question 6

X chromosome inactivation

Answer 6

In homogametic females one of the two chromosomes present in each cell is randomly inactivated at an early stage of development. This inactivation prevents a double dose of gene products which could be harmful to cells.

Question 7

SRY gene

Answer 7

• responsible for producing transcription factors that turn on other genes.
• many of these genes are on other chromosomes
• even though these genes are also found in females, they are only transcribed in males.

Question 8

Hermaphrodites

Answer 8

Species that have functioning male and female reproductive organs in each individual. They produce both male and female gametes and usually have a partner with which to exchange gametes.

Question 9

Environmental factors which can influence sex determination

Answer 9

• size
• competition
• parasitic infection