click below
click below
Normal Size Small Size show me how
Advanced Higher
Unit 2 - Sex Determination
Question | Answer |
---|---|
Name two types of factors that can affect gender | Genetics and environmental |
Name the four environmental factors that affect the sex ratio | Size of organism, incubation temperature, parasitic infections, competition |
Name two types of organisms that use the XY system of gender | Live-bearing mammals and Drosophilia |
State the gender of males and females using the XY system and who is homogametic | Females – homogametic Males – heterogametic |
Give an example of an organism who’s system is the opposite to mammals. | Chickens |
State what gender is more likely to inherit a sex linked disease. | Males |
State the genotype of a normal female, carrier female and affected male (using the letter B or b) affected by a sex linked condition | Normal female XBXB Carrier female XBXb Affected male XbY |
Explain why males are more likely to be affected by sex linked conditions | Males only have one X chromosome, whereas females have two X chromosomes, males cannot mask recessive alleles. |
State the name of the genes that determine maleness on the Y chromosome | SRY gene |
Explain how these genes determine maleness. | The SRY gene produces the hormone testosterone. |
Explain the concept of X inactivation in female tortoise shell cats. | One of the homologous chromosomes randomly inactivates. Inactivation of 50% black and 50% orange alleles causes a patchwork tortoise shell cat. |
Explain why X inactivation is necessary. | Prevents a double dose of gene produced, which can be toxic to cells. |
State the term for two different sex chromosomes. | Heterogametic |
State the term for two of the same sex chromosomes. | Homogametic. |