2k- Sex determination Flashcards
What is the sex of birds, mammals and some insects determined by?
The presence of sex chromosomes
In most mammals what determines development of male characteristics?
The SRY gene on the Y chromosome
What do heterogametic males (XY) lack and what can this result in?
Most of the corresponding homologous alleles on the shorter (Y) chromosome, this can result in sex-linked patterns of inheritance as seen with carrier females and affected males
What happens at an early stage of development in homogametic females (XX)?
One of the two X chromosomes present in each cell is randomly inactivated
What is X chromosome inactivation?
A process by which most of one X chromosome is inactivated
Why is X chromosome inactivation necessary?
It prevents a double dose of gene products, which could be harmful to cells
What can be said about carriers?
They are less likely to be affected by any deleterious mutations on these X chromosomes
The X chromosome inactivated in each cell is random. What does this result in?
Half of the cells in any tissue will have a working copy of the gene in question
What are hermaphrodites?
Species that have functioning male and female reproductive organs in each individual. They produce both male and female gametes and usually have a partner to exchange gametes
What is an advantage of being a hermaphrodite?
If the chance of encountering a partner is an uncommon event, there is no requirement for that partner to be of the opposite sex
For most species genetic factors determine sex and sex ratio, however for some __________ factors come into play?
Environmental
What is environmental sex determination in reptiles controlled by?
Environmental temperature of egg incubation
Sex can change within individuals as a result of what?
- size
- competition
- parasitic infection
In some species the sex ratio of offspring can be adjusted in response to what?
Resource availability, e.g. increased competition
