3. sex determination Flashcards
how is the sex of birds determined?
The sex of birds, mammals and some insects is determined by the presence of sex chromosomes
what determines development of male characteristics?
In most mammals the SRY gene on the Y chromosome determines development of male characteristics
what do heterogametic males lack?
Heterogametic (XY) males lack most of the corresponding homologous alleles on the shorter (Y) chromosome
what does this result in?
This can result in sex-linked patterns of inheritance as seen with carrier females (XBXb) and affected males (XbY)
what is present in homogametic females?
In homogametic females (XX) one of the two X chromosomes present in each cell is randomly inactivated at an early stage of development
what does x chromosome inactivation prevent?
Organisms and evolution
X chromosome inactivation prevents a double dose of gene products, which could be harmful to cells
who are less likely to be affected by deleterious mutations?
Carriers are less likely to be affected by any deleterious mutations on these X chromosomes
why do Half of the cells have a working copy of the gene?
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 questio
what are hermaphrodites?
Hermaphrodites are species that have functioning male and female reproductive organs in each individual
what do hermaphrodites produce?
They produce both male and female gametes and usually have a partner with which to exchange gametes
what is the benefit of being a hermaphrodite?
The benefit to the individual organism is that 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?
For other species, environmental rather than genetic factors determine sex and sex ratio
why can sex change?
Sex can change within individuals of some species as a result of size, competition, or parasitic infection
what can be adjusted in response to resource availability
In some species the sex ratio of offspring can be adjusted in response to resource availability
