KA 3: variation and sexual reproduction: sex determination Flashcards
how is the sex of birds, mammals and some insects determined?
the presence of sex chromosomes
what determines the development of male characteristics in most mammals?
the SRY gene on the Y chromosome
what do heterogametic (XY) males lack? and what does this result in?
most of the corresponding homologous alleles on the shorter (Y) chromosome
sex-linked patterns of inheritance as seen with carrier females (XBXb) and affected males (XbY)
in the homogametic females(XX) what is randomly inactivated at an early stage of development?
one of the two X chromosomes present in each cell
what 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
________ are less likely to be affected by any ________ mutations on these X chromosomes
- carriers
- deleterious
as the X chromosome inactivated in each cell is random….
half of these 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
describe what hermaphrodites produce and what usually happens with them partner wise
- produce both male and female gametes
- usually have a partner with which to exchange gametes
what is a benefit to the individual? (in regards to hermaphrodites)
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 factors determine sex and sex ratio?
environmental rather than genetic factors
what is environmental sex determination in reptiles controlled by?
environmental temperature of egg incubation
where can sex change?
within species as a result of:
-size
-competition
-parasitic infection
how can a species sex ratio of offspring be adjusted?
in response to resource avaliability
