biology - 2.3c - 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 (XY) males lack?
Most of the corresponding homologous alleles on the shorter (Y) chromosome.
What can the lack of corresponding homologous alleles on the shorter (Y) chromosome result in?
Sex-linked patterns of inheritance as seen with carrier females (XBXb) and affected males (XbY).
In homogametic females (XX), what happens at an early stage of development?
One of the two X chromosomes present in each cell is randomly inactivated.
What process is X chromosome inactivation?
A process by which most of one X chromosome is inactivated.
What does X chromosome inactivation prevent?
A double dose of gene products, which could be harmful to cells.
What are carriers less likely to be affected by?
Any deleterious mutations on these X chromosomes.
What happens as the X chromosome inactivated in each cell is random?
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.
What do hermaphrodites produce?
Both male and female gametes and usually have a partner with which to exchange gametes.
What is the benefit to the individual organism?
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 other species, what determines sex and sex ratio?
Environmental rather than genetic factors.
What is environmental sex determination in reptiles controlled by?
Environmental temperature of egg incubation.
What can sex change within individuals of some species as a result of?
Size, competition, or parasitic infection.
